CVE-2026-59725: engine.io — Fix

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.

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CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS — Exploit Prediction

0.0035

Probability of exploitation

0.28%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-404 CWE-404

Affected Products

Vendor	Product	Versions
socket	engine.io	4.1.0 — 6.6.7

References

Advisories & Patches

https://github.com/socketio/socket.io/commit/fc11285e14964c2132d122164bf130c355f60671 https://github.com/socketio/socket.io/security/advisories/GHSA-r635-g3xr-vw7x

Other References

https://github.com/socketio/socket.io/releases/tag/[email protected]

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-59725? +

CVE-2026-59725 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0035, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-59725? +

CVE-2026-59725 affects products from socket, specifically: engine.io. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-59725? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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