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High, CVSS 8.7amended

socket.io allows an unbounded number of binary attachments

CVE-2026-33151GHSA-677m-j7p3-52f9

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (socket.io-parser 4.2.6, 3.4.4, 3.3.5), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • npm socket.io-parser

    Affected
    < 3.3.5>= 3.4.0, < 3.4.4>= 4.0.0, < 4.2.6
    Fixed in
    3.4.4, 4.2.6, 3.3.5

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
8.7 · 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 · score source
EPSS
  • CVE-2026-33151: 0.52% estimated exploitation activity in the next 30 days; percentile 44.42 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Impact 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. Patches | Version range | Used by | Fixed version | |------------------|--------------------------------------------|---------------| | =4.0.0 <4.2.6 | socket.io@4.x and socket.io-client@4.x | 4.2.6 | | =3.4.0 <3.4.4 | socket.io@2.x | 3.4.4 | | <3.3.5 | socket.io-client@2.x | 3.3.5 | Workarounds There is no known workaround except upgrading to a safe version. For more information If you have any questions or comments about this advisory: - Open a discussion here

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-677m-j7p3-52f9

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-677m-j7p3-52f9

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-33151

Advisory: socket.io allows an unbounded number of binary attachments
IDs: CVE-2026-33151, GHSA-677m-j7p3-52f9
Record: https://patchnext.com/advisories/cve-2026-33151 (revision 3, source checked 26 Oct 2026, 12:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: socket.io-parser 4.2.6, 3.4.4, 3.3.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm socket.io-parser: affected < 3.3.5; >= 3.4.0, < 3.4.4; >= 4.0.0, < 4.2.6; fixed in 3.4.4, 4.2.6, 3.3.5

## Suggested inspection (read-only)
- `npm ls socket.io-parser --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on socket.io-parser.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-677m-j7p3-52f9 (OSV record GHSA-677m-j7p3-52f9 lists affected ranges: npm socket.io-parser >=0 =3.4.0 =4.0.0 <4.2.6 (fixed))
- Verified: https://github.com/advisories/GHSA-677m-j7p3-52f9 (GitHub-reviewed advisory GHSA-677m-j7p3-52f9 lists affected ranges: npm socket.io-parser >=0 =3.4.0 =4.0.0 <4.2.6)

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