libp2p: Gossipsub StrictSign accepts attacker-signed messages as a victim RSA peer ID

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-2026-86038: 0.19% estimated exploitation activity in the next 30 days; percentile 8.99 (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 @libp2p/gossipsub StrictSign validation does not bind a supplied message public key to the claimed from peer ID when from is an RSA-style peer ID that does not inline its public key. An attacker can set from to a victim RSA peer ID, sign the message with the attacker's own private key, include the attacker's public key in msg.key, and have the message accepted as a valid signed message from the victim. Details The vulnerable code is in packages/gossipsub/src/utils/buildRawMessage.ts inside validateToRawMessage. When msg.key is present: For RSA peer IDs parsed from the wire from multihash, fromPeerId.publicKey is undefined because the RSA public key is not inlined in the peer ID. This means the key-to-from comparison is skipped. The code then verifies the signature with the attacker-supplied msg.key and returns a signed message whose from is the victim RSA peer ID. The missing invariant is: This check must be performed whenever a public key is supplied, including keyless peer…

Published by the source

17 Sep 2026, 17:29 UTC

Last modified by the source

17 Sep 2026, 17:45 UTC

Source last checked

26 Oct 2026, 13:02 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-c3gv-825q-fvmp

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-c3gv-825q-fvmp

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-c3gv-825q-fvmp

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# Patch Next advisory brief: CVE-2026-86038

Advisory: libp2p: Gossipsub StrictSign accepts attacker-signed messages as a victim RSA peer ID
IDs: CVE-2026-86038, GHSA-c3gv-825q-fvmp
Record: https://patchnext.com/advisories/cve-2026-86038 (revision 3, source checked 26 Oct 2026, 13:02 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: @libp2p/gossipsub 16.0.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @libp2p/gossipsub: affected >= 15.0.0, < 16.0.5; fixed in 16.0.5

## Suggested inspection (read-only)
- `npm ls @libp2p/gossipsub --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 @libp2p/gossipsub.
- 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-c3gv-825q-fvmp (GitHub-reviewed advisory GHSA-c3gv-825q-fvmp lists affected ranges: npm @libp2p/gossipsub >=15.0.0 <16.0.5)
- Verified: https://osv.dev/vulnerability/GHSA-c3gv-825q-fvmp (OSV record GHSA-c3gv-825q-fvmp lists affected ranges: npm @libp2p/gossipsub >=15.0.0 <16.0.5 (fixed))

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