Improper Verification of Cryptographic Signature Affecting altcha package, versions <1.0.0
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-RUBY-ALTCHA-14426455
- published17 Dec 2025
- disclosed16 Dec 2025
- credit饺子w (Yumechi)
Introduced: 16 Dec 2025
CVE-2025-68113 (opens in a new tab)How to fix?
Upgrade altcha to version 1.0.0 or higher.
Overview
altcha is an A lightweight library for creating and verifying ALTCHA challenges.
Affected versions of this package are vulnerable to Improper Verification of Cryptographic Signature via the HMAC computation. An attacker can bypass intended challenge expiration and reuse previously solved challenges by submitting a valid proof-of-work with a modified expiration value, potentially undermining abuse-prevention mechanisms such as rate limiting and bot mitigation.
Workaround
This vulnerability can be mitigated by appending a delimiter to the end of the salt value prior to HMAC computation (for example, <salt>?expires=<time>&), which prevents ambiguity between parameters and the nonce.