CVE-2026-59724: Socket.IO enables bidirectional and low-latency communication for every platform

Q: How do I fix CVE-2026-59724?

engine.io: upgrade to 6.6.7. Exact commands for each OS are on this page.

Q: Is CVE-2026-59724 being exploited?

CVE-2026-59724 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-59724 affect?

CVE-2026-59724 affects engine.io. Severity is high (CVSS 7.5). 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 c

Q: How urgent is CVE-2026-59724?

Priority 43/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2026-59724 is a high-severity flaw (CVSS 7.5) affecting engine.io. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 51%)
CISA exploited list	No
Weakness	CWE-20
Published	2026-07-08
Last modified	2026-10-25

Publisher (CNA): GitHub, Inc. · Vendor: socket

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-08 16:16 UTCPublished CVE record published
2026-10-25 20:10 UTCUpdated Record last modified

socket engine.io UPGRADE

Affected: >= 6.5.0 and < 6.6.7

Fixed in: 6.6.7

Safe to downgrade to: a release before 6.5.0

1. Check installed version

npm ls engine.io

2. UPGRADE to 6.6.7

npm install engine.io@">=6.6.7"

3. If no update is available yet, DOWNGRADE to a release before 6.5.0

npm view engine.io versions npm install engine.io@"<6.5.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-59724?

engine.io: upgrade to 6.6.7. Exact commands for each OS are on this page.

Is CVE-2026-59724 being exploited?

CVE-2026-59724 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-59724 affect?

CVE-2026-59724 affects engine.io. Severity is high (CVSS 7.5). 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 c

How urgent is CVE-2026-59724?

Priority 43/100. High severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-59725 HIGH 7.5 UPGRADE Socket.IO enables bidirectional and low-latency communication for every platform

References

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