CVE-2025-68113

CVE-2025-68113 (ALTCHA) describes a cryptographic semantic binding flaw in ALTCHA libraries where the HMAC does not unambiguously bind challenge parameters to the nonce, enabling potential replay of previously solved challenges depending on server-side handling. Affected components include ALTCHA...

ALTCHA Proof-of-Work Vulnerable to Challenge Splicing and Replay

Impact A cryptographic semantic binding flaw in ALTCHA libraries allows challenge payload splicing, which may enable replay attacks. The HMAC signature does not unambiguously bind challenge parameters to the nonce, allowing an attacker to reinterpret a valid proof-of-work submission with a modifi...