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Δ / VULNERABILITY RECORD

CVE-2025-68113.

Source-reported disclosure and enrichment record.

SEVERITY / CVSSMEDIUM / 6.5CVSS 3.1 · security-advisories@github.com
EXPLOITATION STATUSNot listed in the cached KEV catalogThis does not establish absence of exploitation.
RECORD STATUSDeferredModified Oct 07, 2026

Disclosure summary

ALTCHA is privacy-first software for captcha and bot protection. 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. 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, which include version 1.0.0 of the altcha Golang package, version 1.0.0 of the altcha Rubygem, version 1.0.0 of the altcha pip package, version 1.0.0 of the altcha Erlang package, version 1.4.1 of the altcha-lib npm package, version 1.3.1 of the altcha-org/altcha Composer package, and version 1.3.0 of the org.altcha:altcha Maven package. As a mitigation, implementations may append a delimiter to the end of the `salt` value prior to HMAC computation (for example, `?expires=&`). 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.

Source-reported weakness categories

CWE-115, CWE-347

Source-specific records & product guidance

Sources retain their own attribution and scoring. Follow the original record to confirm affected versions, fixed releases, and configuration conditions.

NIST National Vulnerability Database · NVD-CVE-2025-68113

Open original source · Updated Oct 07, 2026

Only CPE matches marked vulnerable=true are indexed. AND/OR platform conditions must be checked in the original NVD record.

Original records & references

PUBLISHED 2025-12-15T20:15:53-05:00
MODIFIED 2026-10-07T15:10:00-04:00
INGESTED 2026-10-08T12:35:47-04:00