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How the Mentioned CVE Works
This vulnerability exists in the deterministic ECDSA signature generation within the affected Elliptic package, as defined by RFC 6979. The flaw occurs during step 3.2 of the `k` generation process. The interim value for k, which must be a cryptographically secure random integer, is incorrectly processed when it contains leading zero bytes. The package’s byte-length calculation function fails to account for these leading zeros, mistakenly treating them as insignificant. Consequently, the `k` value is truncated before being used in the core signature equation (r, s). This truncation alters the mathematical relationship between the private key, the signature, and the message hash. Signatures produced with a truncated `k` are mathematically invalid for the intended input, breaking legitimate transaction verification. More critically, this deterministic flaw means the same message and key will always produce the same faulty k. If an attacker obtains both a faulty signature (from the vulnerable library) and a correct signature for the identical message and key, they have two different signatures `(r, s)` and `(r, s’)` derived from the same `r` but different `k` values. This specific condition allows for cryptographic lattice attacks. By analyzing these two signatures, an attacker can solve for the original, truncated `k` value. Once `k` is recovered, the signer’s secret private key can be directly calculated using the ECDSA equations, leading to a complete compromise of the key pair.
DailyCVE Form
Platform: Node.js Elliptic
Version: <=6.6.1
Vulnerability: ECDSA `k` truncation
Severity: Low
Date: 2026-01-08
Prediction: 2026-01-15
What Undercode Say
Bash Commands
npm list elliptic
cat package.json | grep elliptic
node -e "console.log(require('elliptic').version)"
Code Snippets
// Example of generating a signature with the vulnerable library
const EC = require('elliptic').ec;
const ec = new EC('secp256k1');
const key = ec.genKeyPair();
const msgHash = 'some_hash';
const signature = key.sign(msgHash); // Potentially flawed if k has leading zeros
// Simplified concept of the flawed length check
function getLength(buffer) {
// Flawed logic that skips leading zeros
let i = 0;
while (buffer[bash] === 0 && i < buffer.length) { i++; }
return buffer.length - i; // This truncation causes the bug
}
How Exploit
- Identify a target using a vulnerable version of the Elliptic library for signing.
- Induce or observe the generation of a digital signature for a known message.
3. Obtain the resulting faulty signature `(r, s_faulty)`.
- Acquire a correct signature `(r, s_correct)` for the same message and key pair, potentially by using a patched library or different implementation.
- Use both signatures in a specialized lattice attack (e.g., using the “LLL” algorithm) to solve for the truncated nonce
k. - Compute the secret private key `d_A` using the formula derived from ECDSA equations with the recovered
k.
Protection from this CVE
- Update the Elliptic package to a version >6.6.1 immediately.
- Implement signature verification using an independent, known-good library for critical operations.
- Monitor for abnormal signature validation failures in logs.
- Rotate any cryptographic keys that may have been used to generate signatures with the vulnerable version.
Impact
1. Broken legitimate signatures causing denial-of-service.
2. Secret private key exposure under specific conditions.
- Compromise of all assets secured by the exposed key.
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Sources:
Reported By: github.com
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