What’s Vulnerable › Vulnerabilities

CVE-2026-33151: socket.io allows an unbounded number of binary attachments

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-03-20 · updated 2026-06-17
• Weakness: CWE-20

Description

Socket.IO is an open source, real-time, bidirectional, event-based, communication framework. Prior to versions 3.3.5, 3.4.4, and 4.2.6, a specially crafted Socket.IO packet can make the server wait for a large number of binary attachments and buffer them, which can be exploited to make the server run out of memory. This issue has been patched in versions 3.3.5, 3.4.4, and 4.2.6.

Affected products

• Socket.io-Parser: before 3.3.5; from 3.4.0 before 3.4.4; from 4.0.0 before 4.2.6 — fixed in 3.3.5, 3.4.4, 4.2.6

How to fix

Upgrade to a fixed version: Socket.io-Parser 3.3.5, 3.4.4, 4.2.6. Check the vendor advisory for mitigations.

References

• https://github.com/socketio/socket.io/commit/719f9ebab0772ffb882bd614b387e585c1aa75d4
• https://github.com/socketio/socket.io/commit/9d39f1f080510f036782f2177fac701cc041faaf
• https://github.com/socketio/socket.io/commit/b25738c416c4e32fbff62ee182afa8f6d0dacf78
• https://github.com/socketio/socket.io/security/advisories/GHSA-677m-j7p3-52f9

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