CVE-2025-68113.yml

---
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