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Fencer Intel
medium 6.5

CVE-2021-20234 json

An uncontrolled resource consumption (memory leak) flaw was found in the ZeroMQ client in versions before 4.3.3 in src/pipe.cpp.

published 5y ago modified 3mo ago also EUVD-2021-7673 , JLSEC-2026-514

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.1%
EPSS 1.1% chance of exploitation in 30 days, percentile 65%
public exploits
0
none known

Summary

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.

Patch / fix

  • julia ZeroMQ_jll 4.3.4+0
  • zeromq libzmq 4.3.3
  • zeromq3 Debian 14, Debian 13, Debian 12 4.3.3-1

debian advisories DEBIAN-CVE-2021-20234

  • zeromq3 Ubuntu Pro 14.04 LTS 4.0.4+dfsg-2ubuntu0.1+esm3
  • zeromq3 Ubuntu Pro 16.04 LTS 4.1.4-7ubuntu0.1+esm2
  • zeromq3 Ubuntu Pro 18.04 LTS 4.2.5-1ubuntu0.2+esm2
  • zeromq3 Ubuntu Pro 20.04 LTS 4.3.2-2ubuntu1.20.04.1~esm2

ubuntu advisories UBUNTU-CVE-2021-20234

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Is CVE-2021-20234 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-20234 updated cvss 5.3

zeromq: Memory leak in client induced by malicious server without CURVE/ZAP

  • Red Hat Ceph Storage 2 zeromq3
    affected: no fix planned “Out of support scope”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.07% chance of exploitation in the next 30 days, higher than 65% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/zeromq/libzmq/security/advisories/GHSA-wfr2-29gj-5w87 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:N/A:P
OSV 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
julia ZeroMQ_jll
<4.3.4+0
4.3.4+0

Affected products

  • n/a zeromq

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption
  • CWE-401 Missing Release of Memory after Effective Lifetime

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.