High severity · published Jul 8, 2026
CVE-2026-59725
Socket.IO: Engine.IO Polling Transport Connection Exhaustion
7.5
CVSS
0.6%
EPSS
No
On KEV
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 vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.6% · higher than 50% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
EN
engine.io · socketio
>= 4.1.0, < 6.6.7 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-59725
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-59725
Patch
https://github.com/socketio/socket.io/commit/fc11285e14964c2132d122164bf130c355f60671
Release Notes
https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.7
Patch
https://github.com/socketio/socket.io/security/advisories/GHSA-r635-g3xr-vw7x
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