altcha-org altcha-lib up to 1.4.0 interpretation input

Summaryinfo

A vulnerability labeled as critical has been found in altcha-org altcha-lib up to 1.4.0. Affected by this vulnerability is an unknown functionality. Executing a manipulation can lead to interpretation input. This vulnerability is handled as CVE-2025-68113. The attack can be executed remotely. There is not any exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as critical was found in altcha-org altcha-lib up to 1.4.0. This vulnerability affects an unknown part. The manipulation with an unknown input leads to a interpretation input vulnerability. The CWE definition for the vulnerability is CWE-115. The product misinterprets an input, whether from an attacker or another product, in a security-relevant fashion. As an impact it is known to affect integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2025-68113 since 12/15/2025. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are neither technical details nor an exploit publicly available.

Upgrading to version 1.4.1 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch 09b2bad466ad0338a5b24245380950ea9918333e is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• altcha-org

Name

• altcha-lib

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4.0

License

• open-source

Website

• Product: https://github.com/altcha-org/altcha-lib/

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