Forge has signature forgery in Ed25519 due to missing S > L check

Exploitation

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

CVSS

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

EPSS

• CVE-2026-33895: 0.53% estimated exploitation activity in the next 30 days; percentile 44.66 (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.

Summary Ed25519 signature verification accepts forged non-canonical signatures where the scalar S is not reduced modulo the group order (S = L). A valid signature and its S + L variant both verify in forge, while Node.js crypto.verify (OpenSSL-backed) rejects the S + L variant, as defined by the specification. This class of signature malleability has been exploited in practice to bypass authentication and authorization logic (see CVE-2026-25793, CVE-2022-35961). Applications relying on signature uniqueness (i.e., dedup by signature bytes, replay tracking, signed-object canonicalization checks) may be bypassed. Impacted Deployments Tested commit: 8e1d527fe8ec2670499068db783172d4fb9012e5 Affected versions: tested on v1.3.3 (latest release) and all versions since Ed25519 was implemented. Configuration assumptions: - Default forge Ed25519 verify API path (ed25519.verify(...)). Root Cause In lib/ed25519.js, cryptosignopen(...) uses the signature's last 32 bytes (S) directly in scalar…

Published by the source

26 Mar 2026, 22:04 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:47 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-q67f-28xg-22rw

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-q67f-28xg-22rw

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# Patch Next advisory brief: CVE-2026-33895

Advisory: Forge has signature forgery in Ed25519 due to missing S > L check
IDs: CVE-2026-33895, GHSA-q67f-28xg-22rw
Record: https://patchnext.com/advisories/cve-2026-33895 (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: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: node-forge 1.4.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm node-forge: affected < 1.4.0; fixed in 1.4.0

## Suggested inspection (read-only)
- `npm ls node-forge --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 node-forge.
- 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-q67f-28xg-22rw (OSV record GHSA-q67f-28xg-22rw lists affected ranges: npm node-forge >=0 <1.4.0 (fixed))
- Verified: https://github.com/advisories/GHSA-q67f-28xg-22rw (GitHub-reviewed advisory GHSA-q67f-28xg-22rw lists affected ranges: npm node-forge >=0 <1.4.0)

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