StableLib Ed25519 Signature Malleability via Missing S < L Check

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

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Ed25519 Signature Malleability via Missing S < L Check -- Same Class as node-forge CVE-2026-33895 (CWE-347) Target - Repository: StableLib/stablelib (package: @stablelib/ed25519) - Platform: GitHub PVR - Bounty: CVE credit - CWE: CWE-347 (Improper Verification of Cryptographic Signature) - Version: 2.0.2 (latest, 2026-03-28) Root Cause The verify() function in @stablelib/ed25519 does not check that the S component of the signature is less than the group order L. Per CFRG recommendations and the ZIP-215 specification, Ed25519 implementations should reject signatures where S = L to prevent signature malleability. When S = L, [S]B = [(S mod L)]B = [(S - L)]B, meaning two different 32-byte S values produce the same verification result. An attacker who observes a valid signature (R, S) can produce a second valid signature (R, S + L) for the same message. Vulnerable code File: packages/ed25519/ed25519.ts (compiled: lib/ed25519.js:779-802) Note that h is properly reduce()d (line 794), but S…

Published by the source

1 Apr 2026, 22:13 UTC

Last modified by the source

7 Apr 2026, 14:35 UTC

Source last checked

26 Oct 2026, 12:47 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-x3ff-w252-2g7j

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-x3ff-w252-2g7j

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# Patch Next advisory brief: GHSA-x3ff-w252-2g7j

Advisory: StableLib Ed25519 Signature Malleability via Missing S < L Check
IDs: GHSA-x3ff-w252-2g7j
Record: https://patchnext.com/advisories/ghsa-x3ff-w252-2g7j (revision 2, source checked 26 Oct 2026, 12:47 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 response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @stablelib/ed25519: affected <= 2.0.2

## Suggested inspection (read-only)
- `npm ls @stablelib/ed25519 --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @stablelib/ed25519.
- 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/GHSA-x3ff-w252-2g7j (OSV record GHSA-x3ff-w252-2g7j lists affected ranges: npm @stablelib/ed25519 >=0 <=2.0.2)
- Verified: https://github.com/advisories/GHSA-x3ff-w252-2g7j (GitHub-reviewed advisory GHSA-x3ff-w252-2g7j lists affected ranges: npm @stablelib/ed25519 >=0 <=2.0.2)

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