VulnerabilityAnalyzed

CVE-2026-59725

From 4.1.0 before 6.6.7, Engine.IO protocol v4 polling transport does not properly close the HTTP response for invalid binary POST requests with Content-Type: application/octet-stream, allowing an unauthenticated attacker to exhaust server-side…

HIGH 7.5EPSS 0.64%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (0.64%). 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 4.1.0 before 6.6.7, Engine.IO protocol v4 polling transport does not properly close the HTTP response for invalid binary POST requests with Content-Type: application/octet-stream, allowing an unauthenticated attacker to exhaust server-side connections and sockets. 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: 0.64% probability · 49th percentile
CISA KEV: Not listed
Weakness: CWE-404
Affected: socket/engine.io
Source: security-advisories@github.com

References

https://github.com/socketio/socket.io/commit/fc11285e14964c2132d122164bf130c355f60671Patch
https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.7Release Notes
https://github.com/socketio/socket.io/security/advisories/GHSA-r635-g3xr-vw7xPatch, Vendor Advisory

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