CVE-2021-4236: Web Sockets do not execute any AuthenticateMethod methods which may be set, leading to a nil pointer dereferen

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2021-4236 is a critical-severity flaw (CVSS 9.8) affecting web. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Web Sockets do not execute any AuthenticateMethod methods which may be set, leading to a nil pointer dereference if the returned UserData pointer is assumed to be non-nil, or authentication bypass. This issue only affects WebSockets with an AuthenticateMethod hook. Request handlers that do not explicitly use WebSockets are not vulnerable.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.2% (top 32%)
CISA exploited list	No
Weakness	CWE-476
Published	2022-12-27
Last modified	2026-06-17

Publisher (CNA): Go Project · Vendor: web project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2022-12-27 22:15 UTCPublished CVE record published
2026-06-17 04:19 UTCUpdated Record last modified

web project web UPGRADE

Affected: >= 1.4.0 and < 1.5.2

Fixed in: 1.5.2

Safe to downgrade to: a release before 1.4.0

1. Check installed version

apt-cache policy web || rpm -q web || web --version

2. UPGRADE to 1.5.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade web

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade web

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 1.4.0 (Debian / Ubuntu)

apt-cache madison web sudo apt install web=<VERSION_BEFORE_1.4.0> sudo apt-mark hold web

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list web sudo dnf downgrade web-<VERSION_BEFORE_1.4.0> sudo dnf versionlock add web

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-2021-4236?

web: upgrade to 1.5.2. Exact commands for each OS are on this page.

Is CVE-2021-4236 being exploited?

CVE-2021-4236 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-2021-4236 affect?

CVE-2021-4236 affects web. Severity is critical (CVSS 9.8). Web Sockets do not execute any AuthenticateMethod methods which may be set, leading to a nil pointer dereference if the returned UserData pointer is assumed to be non-nil, or authentication bypass. This issue only affects WebSockets with an

How urgent is CVE-2021-4236?

Priority 61/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

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CVE-2025-8220 HIGH 7.3 UPGRADE A vulnerability has been found in Engeman Web up to 12.0.0.2
CVE-2018-25041 MEDIUM 6.3 MITIGATE A vulnerability was found in uTorrent
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References

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