Is CVE-2026-49866 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-49866 being exploited in the wild.

How severe is CVE-2026-49866?

High severity, with a CVSS score of 7.5, published 8 July 2026.

Which products and versions are affected?

Libp2p Gossipsub < 16.0.0; @libp2p/gossipsub (npm) < 16.0.0, SEMVER:introduced=0,fixed=16.0.0.

Is there a fix for CVE-2026-49866?

Yes. @libp2p/gossipsub (npm): upgrade to 16.0.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-49866 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-49866?

Check whether you run Libp2p Gossipsub or @libp2p/gossipsub (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-49866: libp2p gossipsub denial of service via oversized control messages

Q: Which products and versions are affected?

Libp2p Gossipsub < 16.0.0; @libp2p/gossipsub (npm) < 16.0.0, SEMVER:introduced=0,fixed=16.0.0.

Q: Is there a fix for CVE-2026-49866?

Yes. @libp2p/gossipsub (npm): upgrade to 16.0.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-49866 attacked?

It is attacked over the network, in a software library.

Q: Am I affected by CVE-2026-49866?

Check whether you run Libp2p Gossipsub or @libp2p/gossipsub (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-49866 · Severity: high · CVSS 7.5 · Published 2026-07-08

A vulnerability in the libp2p gossipsub library, used by blockchain and peer-to-peer applications like Ethereum clients and IPFS, allows an attacker to crash or freeze a node. By sending specially crafted network messages with an excessive number of identifiers, an attacker can overwhelm the system's processor. This results in a denial-of-service where the affected node can no longer process transactions, participate in the network, or respond to legitimate users.

Technologies: Libp2p Gossipsub, @libp2p/gossipsub (npm). Vendors: Libp2p, npm.

Quick answers

Is CVE-2026-49866 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-49866 being exploited in the wild.
How severe is CVE-2026-49866?: High severity, with a CVSS score of 7.5, published 8 July 2026.
Which products and versions are affected?: Libp2p Gossipsub < 16.0.0; @libp2p/gossipsub (npm) < 16.0.0, SEMVER:introduced=0,fixed=16.0.0.
Is there a fix for CVE-2026-49866?: Yes. @libp2p/gossipsub (npm): upgrade to 16.0.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-49866 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-49866?: Check whether you run Libp2p Gossipsub or @libp2p/gossipsub (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

@libp2p/gossipsub (npm): upgrade to 16.0.0 or later
```
npm install @libp2p/gossipsub@16.0.0
```

Technical details

The vulnerability exists in the gossipsub implementation of js-libp2p where IHAVE and IWANT control messages are processed synchronously without a decode-time cap on the number of message IDs. The default configuration sets limits like maxIhaveMessageIDs and maxIwantMessageIDs to Infinity. An attacker can send a 4MB RPC frame containing approximately 180,000 message IDs; the victim iterates through every ID before applying any truncation or rate limits. For IWANT messages, there is no per-peer rate limit, allowing a single connection to maintain high CPU utilization indefinitely. For IHAVE messages, an attacker can use approximately 10 Sybil peers to achieve a total event-loop stall. The issue is resolved in version 16.0.0 by introducing finite default limits for RPC decoding.

Affected products

libp2p @libp2p/gossipsub < 16.0.0

Identifiers

CVE-2026-49866
GHSA-cwc9-cp4j-mcvv

Timeline

2026-06-14: advisory: Initial GitHub Advisory published
2026-07-10: patched: Vulnerability updated and patched in version 16.0.0

References

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