CVE-2021-20237

Name: CVE-2021-20237
Creator: NVD / NIST
Published: 2021-05-28T11:15:07.97+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 1.69%

Last modified Jun 17, 2026

CVE-2021-20237 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. An uncontrolled resource consumption (memory leak) flaw was found in ZeroMQ's src/xpub.cpp in versions before 4.3.3. This flaw allows a remote unauthenticated attacker to send crafted PUB messages that consume excessive memory if the CURVE/ZAP authentication is disabled on the server, causing a denial of service. EPSS estimates a 1.69% chance of exploitation in the next 30 days.

Description

An uncontrolled resource consumption (memory leak) flaw was found in ZeroMQ's src/xpub.cpp in versions before 4.3.3. This flaw allows a remote unauthenticated attacker to send crafted PUB messages that consume excessive memory if the CURVE/ZAP authentication is disabled on the server, causing a denial of service. The highest threat from this vulnerability is to system availability.

Metrics

CVSS 3.1

7.5/10

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

EPSS Probability

1.69%

74.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Zeromq	Libzmq	>= 4.2.0, < 4.3.3

References

https://bugzilla.redhat.com/show_bug.cgi?id=1921989Issue Tracking, Third Party Advisory
https://github.com/zeromq/libzmq/security/advisories/GHSA-4p5v-h92w-6wxwPatch, Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1921989Issue Tracking, Third Party Advisory
https://github.com/zeromq/libzmq/security/advisories/GHSA-4p5v-h92w-6wxwPatch, Third Party Advisory

Timeline

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

Frequently Asked Questions

What is CVE-2021-20237?

How severe is CVE-2021-20237?

CVE-2021-20237 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 1.69% probability of exploitation in the next 30 days.

How do I fix CVE-2021-20237?

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-2021-20237?

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

Scan your code now

Source: NVD / NIST