What is CVE-2026-59725?

CVE-2026-59725 is a high-severity vulnerability in Socket Engine.io, classified under Improper Resource Shutdown or Release. CVSS score: 7.5/10. Published 2026-07-08.

How severe is CVE-2026-59725?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Socket Engine.io

CVE-2026-59725

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.

Published 2026-07-08 · last modified 2026-07-13.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.006 (48.9th percentile), scored 2026-10-09.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 49th percentile — 48.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000

Affected products

Socket Engine.io
Socketio Socket.io — versions >= 4.1.0, < 6.6.7

Weakness classification (CWE)

CWE-404 — Improper Resource Shutdown or Release

References

github.com/socketio/socket.io/security/advisories/GHSA-r635-g3xr-vw7x (Patch, Vendor Advisory)
github.com/socketio/socket.io/commit/fc11285e14964c2132d122164bf130c355f60671 (Patch)
github.com/socketio/socket.io/releases/tag/engine.io@6.6.7 (Release Notes)

Frequently asked questions

What is CVE-2026-59725?: CVE-2026-59725 is a high-severity vulnerability in Socket Engine.io, classified under Improper Resource Shutdown or Release. CVSS score: 7.5/10. Published 2026-07-08.
How severe is CVE-2026-59725?: High severity. CVSS v3 base score is 7.5 out of 10.