What is CVE-2021-20237?

CVE-2021-20237 is a high-severity vulnerability in Zeromq Libzmq, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2021-05-28.

How severe is CVE-2021-20237?

High severity. CVSS v3 base score is 7.5 out of 10.

Resource exhaustion in Zeromq Libzmq

CVE-2021-20237

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.

Vulnerability class: DoS (Denial of Service)

Published 2021-05-28 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.017 (76.2th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 76th percentile — 76.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.017 · newest: 0.017 · change: 0.000

Affected products

Zeromq Libzmq
Zeromq — versions zeromq 4.3.3

Weakness classification (CWE)

References

bugzilla.redhat.com/show_bug.cgi (Third Party Advisory, Issue Tracking)
github.com/zeromq/libzmq/security/advisories/GHSA-4p5v-h92w-6wxw (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-20237?: CVE-2021-20237 is a high-severity vulnerability in Zeromq Libzmq, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2021-05-28.
How severe is CVE-2021-20237?: High severity. CVSS v3 base score is 7.5 out of 10.