CVE-2026-49866 libp2p: CPU DoS via oversized IHAVE and IWANT control message arrays
Attackers can cause CPU exhaustion and block the Node.js event loop by sending oversized gossipsub control messages, requiring an upgrade to libp2p.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-49866?
CVE-2026-49866 is a high-severity denial of service vulnerability in js-libp2p, published on 8 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
libp2p is a JavaScript Implementation of libp2p networking stack. Prior to 16.0.0, @libp2p/gossipsub defaultDecodeRpcLimits set maxIhaveMessageIDs and maxIwantMessageIDs to Infinity, allowing oversized IHAVE and IWANT control message arrays in message/decodeRpc.ts and gossipsub.ts to synchronously iterate roughly 180,000 message IDs per 4 MB frame and block the Node.js event loop. This issue is fixed in version 16.0.0.
Weakness: CWE-770
Which versions are affected by CVE-2026-49866?
2 open source packages ship an affected version, including @libp2p/gossipsub.
| Package | Affected | Fixed in |
|---|---|---|
@libp2p/gossipsub npm | All versions | 16.0.0 |
@libp2p/gossipsub npm | All versions | 16.0.0 |
How do I fix CVE-2026-49866?
Upgrade @libp2p/gossipsub to 16.0.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-49866 being exploited?
There is no known exploitation of CVE-2026-49866 in the wild and no public exploit code.
Sources
Also known as GHSA-cwc9-cp4j-mcvv.