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Fencer Intel
high 7.5

CVE-2026-59724 json

Socket.IO: Engine.IO WebTransport SID DoS

published 4mo ago modified 17d ago also EUVD-2026-42312 , GHSA-gr94-w7qr-f4j3

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 49%
public exploits
0
none known

Summary

Socket.IO enables bidirectional and low-latency communication for every platform. From 6.5.0 before 6.6.7, Engine.IO servers with WebTransport enabled can resolve a crafted session ID such as __proto__ through an inherited property of the clients object during WebTransport upgrade handling, causing a TypeError and denial of service. This issue is fixed in version 6.6.7.

Patch / fix

  • npm engine.io 6.6.7
  • socket engine.io 6.6.7
  • dotnet8.0 hummingbird 1 8.0.128-1.hum1
  • dotnet-sdk-8.0 hummingbird 1 8.0.128-1.hum1
  • dotnet-sdk-dbg-8.0 hummingbird 1 8.0.128-1.hum1
  • dotnet-templates-8.0 hummingbird 1 8.0.128-1.hum1
  • dotnet-sdk-8.0-source-built-artifacts hummingbird 1 8.0.128-1.hum1

red hat advisories RHSA-2026:26994

Is CVE-2026-59724 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-59724 updated cvss 7.5

engine.io: Engine.IO: Denial of Service via crafted WebTransport session ID

  • Red Hat Enterprise Linux AI (RHEL AI) 3 rhelai3/bootc-cuda-rhel9, rhelai3/bootc-rocm-rhel9, rhelai3/bootc-gaudi-rhel9, rhelai3/disk-image-cuda-rhel9
    affected: no fix available, no fix planned “Will not fix”
  • Red Hat Hardened Images dotnet8.0 8.0.128-1.hum1, dotnet-sdk-8.0 8.0.128-1.hum1, dotnet-sdk-dbg-8.0 8.0.128-1.hum1, dotnet-templates-8.0 8.0.128-1.hum1, dotnet-sdk-8.0-source-built-artifacts 8.0.128-1.hum1
    fixed: vendor fix RHSA-2026:26994
  • Red Hat Hardened Images dotnet-hostfxr-8.0 8.0.28-1.hum1, dotnet-runtime-8.0 8.0.28-1.hum1, aspnetcore-runtime-8.0 8.0.28-1.hum1, dotnet-runtime-dbg-8.0 8.0.28-1.hum1, dotnet-apphost-pack-8.0 8.0.28-1.hum1, dotnet-targeting-pack-8.0 8.0.28-1.hum1, +2 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
4mo ago

Exploit prediction

0.61% chance of exploitation in the next 30 days, higher than 49% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
npm engine.io
>=6.5.0, <6.6.7
6.6.7

Affected products

  • socketio socket.io

Classification

Weakness
  • CWE-20 Improper Input Validation

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of socketio/socket.io published their own advisory on GitHub. Reviewed sources take precedence over it.