libp2p: CPU DoS via oversized IHAVE and IWANT control message arrays

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:N/A:H

EPSS

• CVE-2026-49866: 0.63% estimated exploitation activity in the next 30 days; percentile 50.24 (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 gossipsub processes IHAVE and IWANT control messages by iterating every received message ID synchronously before doing anything with the results. There is no cap on how many IDs a single frame may contain. The default LP frame limit is 4MB, which fits roughly 180,000 message IDs. Iterating that many IDs blocks the Node.js event loop for around 200ms per call. The two variants have different severity. For IHAVE there is a per-peer per-heartbeat counter that limits each peer to one full iteration per heartbeat, so causing a total stall requires around 10 Sybil peers. For IWANT there is no equivalent counter at all, so a single peer continuously streaming 4MB frames can hold the event loop above 80% utilisation indefinitely. Details No decode-time cap on message ID count (message/decodeRpc.ts:11-19) These are the defaults unless the operator explicitly overrides opts.decodeRpcLimits. A TODO at gossipsub.ts:857 already notes the gap: // TODO: Check max gossip message size, before…

Published by the source

10 Jul 2026, 16:04 UTC

Last modified by the source

10 Jul 2026, 16:15 UTC

Source last checked

26 Oct 2026, 12:56 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-cwc9-cp4j-mcvv

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-cwc9-cp4j-mcvv

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# Patch Next advisory brief: CVE-2026-49866

Advisory: libp2p: CPU DoS via oversized IHAVE and IWANT control message arrays
IDs: CVE-2026-49866, GHSA-cwc9-cp4j-mcvv
Record: https://patchnext.com/advisories/cve-2026-49866 (revision 2, source checked 26 Oct 2026, 12:56 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 16.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @libp2p/gossipsub: affected < 16.0.0; fixed in 16.0.0

## 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://osv.dev/vulnerability/GHSA-cwc9-cp4j-mcvv (OSV record GHSA-cwc9-cp4j-mcvv lists affected ranges: npm @libp2p/gossipsub >=0 <16.0.0 (fixed))
- Verified: https://github.com/advisories/GHSA-cwc9-cp4j-mcvv (GitHub-reviewed advisory GHSA-cwc9-cp4j-mcvv lists affected ranges: npm @libp2p/gossipsub >=0 <16.0.0)

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