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CWE-115Weakness · CWE-115

CVE-2025-68113

MEDIUM · 6.5 CVSS v3.1 Published 2025-12-16
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
74/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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, `<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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis

A detailed technical summary for this CVE is being prepared.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Patch available Apply the vendor patch
Vendor patch github.com →
Recommended fix Moderate confidence

Upgrade to altcha library version 1.0.0 (Golang/Ruby/pip/Erlang), 1.4.1 (npm altcha-lib), 1.3.1 (Composer), or 1.3.0 (Maven)

  1. Identify which ALTCHA library package is in use (Golang, Ruby, Python/pip, Erlang, npm, Composer, or Maven)
  2. Locate the project's dependency configuration file (go.mod, Gemfile, requirements.txt/pip, rebar.config, package.json, composer.json, or pom.xml)
  3. Update the altcha dependency to the fixed version: 1.0.0 for Golang/Ruby/pip/Erlang, 1.4.1 for npm (altcha-lib), 1.3.1 for Composer, or 1.3.0 for Maven
  4. Run package manager update commands (e.g., go get, bundle update, pip install, npm update, composer update)
  5. Rebuild and redeploy the application
  6. Verify that challenge submissions work correctly after the upgrade by testing a challenge flow
Caveat The upgrade should be backward-compatible as the fix adds semantic separation during HMAC computation; however, test thoroughly in a staging environment before production deployment

Generated from the published advisory — verify against the referenced sources before acting.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

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Peer-ranked notes from engineers who’ve handled CVE-2025-68113 in production — separate from our analysis above.

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