CVE-2026-102599 Socket.IO: Engine.IO Protocol Revision Mismatch DoS
A malicious client can cause a Node.js process crash via a crafted Engine.IO protocol revision mismatch during transport upgrade.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-102599?
CVE-2026-102599 is a high-severity denial of service vulnerability in socketio socket.io, published on 13 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Socket.IO enables bidirectional and low-latency communication for every platform. From Engine.IO 6.6.0 until 6.6.10, a transport upgrade can independently derive an Engine.IO protocol revision from the upgrade request instead of enforcing the revision stored on the existing session. A malicious client can establish a valid session and send an upgrade request with a different or omitted EIO query parameter, attaching a transport with incompatible parser and heartbeat behavior. A crafted heartbeat packet can then trigger an uncaught exception and terminate the Node.js process, including when Engine.IO v3 compatibility is disabled because an omitted EIO value is interpreted as revision 3 on the affected path. This issue is fixed in Engine.IO 6.6.10.
Weakness: CWE-248
Which versions are affected by CVE-2026-102599?
2 open source packages ship an affected version, including engine.io.
| Package | Affected | Fixed in |
|---|---|---|
engine.io npm | From 6.6.0 | 6.6.10 |
engine.io npm | From 6.6.0 | 6.6.10 |
How do I fix CVE-2026-102599?
Upgrade engine.io to 6.6.10 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-2026-102599 being exploited?
There is no known exploitation of CVE-2026-102599 in the wild and no public exploit code.
Sources
Also known as GHSA-2gc4-cqfq-p2gv, MINI-x3vm-2xqf-rm69.