ML-DSA Signature Verification Accepts Signatures with Repeated Hint Indices

Exploitation

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

CVSS

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

EPSS

• CVE-2026-24850: 0.34% estimated exploitation activity in the next 30 days; percentile 26.91 (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.

Affected Crate: ml-dsa Affected Versions: v0.1.0-rc.2 (and commits since b01c3b7) Severity: Medium Reporter: Oren Yomtov (Fireblocks) Summary The ML-DSA signature verification implementation in the RustCrypto ml-dsa crate incorrectly accepts signatures with repeated (duplicate) hint indices. According to the ML-DSA specification (FIPS 204 / RFC 9881), hint indices within each polynomial must be strictly increasing. The current implementation uses a non-strict monotonic check (<= instead of <), allowing duplicate indices. Note: This is a regression bug. The original implementation was correct, but commit b01c3b7 ("Make ML-DSA signature decoding follow the spec (#895)", fixing issue #894) inadvertently changed the strict < comparison to <=, introducing the vulnerability. Vulnerability Details Root Cause The vulnerability is located in the monotonic helper function in ml-dsa/src/hint.rs: The comparison operator <= allows equal consecutive values, meaning duplicate hint indices are not…

Published by the source

28 Jan 2026, 16:44 UTC

Last modified by the source

28 Jan 2026, 16:44 UTC

Source last checked

26 Oct 2026, 15:39 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-5x2r-hc65-25f9

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# Patch Next advisory brief: CVE-2026-24850

Advisory: ML-DSA Signature Verification Accepts Signatures with Repeated Hint Indices
IDs: CVE-2026-24850, GHSA-5x2r-hc65-25f9
Record: https://patchnext.com/advisories/cve-2026-24850 (revision 1, source checked 26 Oct 2026, 15:39 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: ml-dsa 0.1.0-rc.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io ml-dsa: affected >= 0.0.4, < 0.1.0-rc.4; fixed in 0.1.0-rc.4

## Suggested inspection (read-only)
- crates.io ml-dsa: check the installed version with your package manager.

## 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 ml-dsa.
- 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://github.com/advisories/GHSA-5x2r-hc65-25f9 (GitHub-reviewed advisory GHSA-5x2r-hc65-25f9 lists affected ranges: crates.io ml-dsa >=0.0.4 <0.1.0-rc.4)

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