VulnerabilityAnalyzed

CVE-2026-59724

From 6.5.0 before 6.6.7, Engine.IO servers with WebTransport enabled can resolve a crafted session ID such as __proto__ through an inherited property of the clients object during WebTransport upgrade handling, causing a TypeError and denial of service.

HIGH 7.5EPSS 0.61%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (0.61%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.

Description

Socket.IO enables bidirectional and low-latency communication for every platform. From 6.5.0 before 6.6.7, Engine.IO servers with WebTransport enabled can resolve a crafted session ID such as __proto__ through an inherited property of the clients object during WebTransport upgrade handling, causing a TypeError and denial of service. This issue is fixed in version 6.6.7.

CVSS 3.1: 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS: 0.61% probability · 47th percentile
CISA KEV: Not listed
Weakness: CWE-20
Affected: socket/engine.io
Source: security-advisories@github.com

References

https://github.com/socketio/socket.io/commit/1fa1f46cd420ac5b57bb4c04c959b58f3c79158cPatch
https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.7Release Notes
https://github.com/socketio/socket.io/security/advisories/GHSA-gr94-w7qr-f4j3Patch, Vendor Advisory, Mitigation

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.