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How the CVE Works:
The vulnerability exists in Altcha’s Proof-of-Work (PoW) obfuscation mode. This mode is designed to hide the original PoW nonce by applying a mathematical transformation. However, the transformation algorithm is cryptographically weak. An attacker can analyze the obfuscated output sent to the client and, through mathematical deduction, reverse the obfuscation process. This recovery of the original secret nonce can be performed in constant time, regardless of the PoW difficulty, fundamentally breaking the security premise. The attacker can then forge valid PoW solutions without performing the required computational work, potentially bypassing anti-abuse mechanisms.
Platform: Altcha
Version: 0.8.0+
Vulnerability: Nonce Recovery
Severity: Moderate
date: Dec 8-9 2025
Prediction: Patch expected Dec 16 2025
What Undercode Say:
Analytics:
curl -s https://api.github.com/advisories | jq '.[] | select(.package.slug=="altcha")'
// Sample of weak obfuscation logic const weakObfuscate = (nonce) => (nonce CONST + OFFSET) % MODULUS;
How Exploit:
Attacker visits protected page, receives obfuscated challenge, applies mathematical deduction to derive original nonce, submits solved challenge without computational work, bypassing rate-limiting or anti-spam.
Protection from this CVE:
Disable obfuscation mode, upgrade library, implement server-side nonce validation, use standard cryptographic hashing.
Impact:
Spam bypass, resource exhaustion, broken anti-abuse, integrity loss.
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Sources:
Reported By: github.com
Extra Source Hub:
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