ALTCHA Proof-of-Work Vulnerable to Challenge Splicing and Replay

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2025-68113: 0.46% estimated exploitation activity in the next 30 days; percentile 40.14 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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,…

Published by the source

7 Jul 2026, 16:03 UTC

Last modified by the source

7 Jul 2026, 17:56 UTC

Source last checked

26 Oct 2026, 12:41 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-6gvq-jcmp-8959

2. Revision 1 · created · 24 Oct 2026

   Published from osv record PYSEC-2026-1115

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# Patch Next advisory brief: CVE-2025-68113

Advisory: ALTCHA Proof-of-Work Vulnerable to Challenge Splicing and Replay
IDs: CVE-2025-68113, GHSA-6gvq-jcmp-8959
Record: https://patchnext.com/advisories/cve-2025-68113 (revision 2, source checked 26 Oct 2026, 12:41 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: altcha 1.0.0; altcha 1.0.0; altcha-org/altcha 1.3.1; github.com/altcha-org/altcha-lib-go 1.0.0; org.altcha:altcha 1.3.0; altcha-lib 1.4.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems altcha: affected < 1.0.0; fixed in 1.0.0
- PyPI altcha: affected < 1.0.0; fixed in 1.0.0
- Packagist altcha-org/altcha: affected < 1.3.1; fixed in 1.3.1
- Go github.com/altcha-org/altcha-lib-go: affected < 1.0.0; fixed in 1.0.0
- Maven org.altcha:altcha: affected < 1.3.0; fixed in 1.3.0
- npm altcha-lib: affected < 1.4.1; fixed in 1.4.1

## Suggested inspection (read-only)
- RubyGems altcha: check the installed version with your package manager.
- `python -m pip show altcha`: prints the installed version. Run with the environment that serves production active.
- Packagist altcha-org/altcha: check the installed version with your package manager.
- Go github.com/altcha-org/altcha-lib-go: check the installed version with your package manager.
- Maven org.altcha:altcha: check the installed version with your package manager.
- `npm ls altcha-lib --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on altcha, altcha-org/altcha, github.com/altcha-org/altcha-lib-go, org.altcha:altcha, altcha-lib.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/PYSEC-2026-1115 (OSV record PYSEC-2026-1115 lists affected ranges: PyPI altcha >=0 <1.0.0 (fixed))
- Verified: https://github.com/advisories/GHSA-6gvq-jcmp-8959 (GitHub-reviewed advisory GHSA-6gvq-jcmp-8959 lists affected ranges: npm altcha-lib >=0 =0 =0 =0 =0 =0 <1.0.0)

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