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58 changes: 58 additions & 0 deletions gems/altcha/CVE-2025-68113.yml
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---
gem: altcha
cve: 2025-68113
ghsa: 6gvq-jcmp-8959
url: https://github.com/altcha-org/altcha-lib/security/advisories/GHSA-6gvq-jcmp-8959
title: ALTCHA Proof-of-Work Vulnerable to Challenge Splicing and Replay
date: 2025-12-16
description: |
### 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 modified expiration value.

This may allow previously solved challenges to be reused beyond
their intended lifetime, depending on server-side replay handling
and deployment assumptions.

The vulnerability primarily impacts abuse-prevention mechanisms such
as rate limiting and bot mitigation.

It does not directly affect data confidentiality or integrity.

### Patches

This issue has been addressed by enforcing explicit semantic
separation between challenge parameters and the nonce during
HMAC computation.

Users are advised to upgrade to patched versions.

### Workarounds

As a mitigation, implementations may append a delimiter to the
end of the `salt` value prior to HMAC computation (for example,
`<salt>?expires=<time>&`). This prevents ambiguity between
parameters and the nonce and is backward-compatible with existing
implementations, as the delimiter is treated as a standard URL
parameter separator."
cvss_v3: 6.5
patched_versions:
- ">= 1.0.0"
related:
url:
- https://nvd.nist.gov/vuln/detail/CVE-2025-68113
- https://github.com/altcha-org/altcha-lib/security/advisories/GHSA-6gvq-jcmp-8959
- https://github.com/altcha-org/altcha-lib-ex/commit/09b2bad466ad0338a5b24245380950ea9918333e
- https://github.com/altcha-org/altcha-lib-go/commit/4a5610745ef79895a67bac858b2e4f291c2614b8
- https://github.com/altcha-org/altcha-lib-java/commit/69277651fdd6418ae10bf3a088901506f9c62114
- https://github.com/altcha-org/altcha-lib-php/commit/9e9e70c864a9db960d071c77c778be0c9ff1a4d0
- https://github.com/altcha-org/altcha-lib-rb/commit/4fd7b64cbbfc713f3ca4e066c2dd466e3b8d359b
- https://github.com/altcha-org/altcha-lib/commit/cb95d83a8d08e273b6be15e48988e7eaf60d5c08
- https://github.com/altcha-org/altcha-lib-java/releases/tag/v1.3.0
- https://github.com/altcha-org/altcha-lib-php/releases/tag/v1.3.1
- https://github.com/altcha-org/altcha-lib/releases/tag/1.4.1
- https://github.com/advisories/GHSA-6gvq-jcmp-8959