What is CVE-2021-20234?

CVE-2021-20234 is a medium-severity vulnerability in Zeromq Libzmq, classified under Uncontrolled Resource Consumption. CVSS score: 6.5/10. Published 2021-04-01.

How severe is CVE-2021-20234?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Resource exhaustion in Zeromq Libzmq

CVE-2021-20234

An uncontrolled resource consumption (memory leak) flaw was found in the ZeroMQ client in versions before 4.3.3 in src/pipe.cpp. This issue causes a client that connects to multiple malicious or compromised servers to crash. The highest threat from this vulnerability is to system availability.

Vulnerability class: DoS (Denial of Service)

Published 2021-04-01 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.011 (63.6th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 64th percentile — 63.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.011 · newest: 0.011 · change: 0.000

Affected products

Zeromq Libzmq
Zeromq — versions zeromq 4.3.3

Weakness classification (CWE)

References

bugzilla.redhat.com/show_bug.cgi (Patch, Third Party Advisory, Issue Tracking)
github.com/zeromq/libzmq/security/advisories/GHSA-wfr2-29gj-5w87 (Exploit, Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-20234?: CVE-2021-20234 is a medium-severity vulnerability in Zeromq Libzmq, classified under Uncontrolled Resource Consumption. CVSS score: 6.5/10. Published 2021-04-01.
How severe is CVE-2021-20234?: Medium severity. CVSS v3 base score is 6.5 out of 10.