CVE-2021-20236

Name: CVE-2021-20236
Creator: NVD / NIST
Published: 2021-05-28T11:15:07.933+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 1.60%

Last modified Jun 17, 2026

CVE-2021-20236 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. EPSS estimates a 1.60% chance of exploitation in the next 30 days.

Description

A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

1.60%

72.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Zeromq	Zeromq	< 4.3.3
Redhat	Ceph Storage	2.0
Redhat	Enterprise Linux	7.0
Fedoraproject	Fedora	33

References

https://bugzilla.redhat.com/show_bug.cgi?id=1921976Issue Tracking, Third Party Advisory
https://github.com/zeromq/libzmq/security/advisories/GHSA-qq65-x72m-9wr8Patch, Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1921976Issue Tracking, Third Party Advisory
https://github.com/zeromq/libzmq/security/advisories/GHSA-qq65-x72m-9wr8Patch, Third Party Advisory

Timeline

Published: May 28, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-20236?

How severe is CVE-2021-20236?

CVE-2021-20236 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 1.60% probability of exploitation in the next 30 days.

How do I fix CVE-2021-20236?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-20236?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST