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Fencer Vulns
high 7.5

CVE-2021-20237 json

An uncontrolled resource consumption (memory leak) flaw was found in ZeroMQ's src/xpub.cpp in versions before 4.3.3.

published 2021-05-28 5 y ago modified 2026-07-25 3 mo ago also EUVD-2021-7676 , JLSEC-2026-517

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.7%
EPSS 1.7% chance of exploitation in 30 days, percentile 77%
public exploits
0
none known

Summary

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.

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-2021-20237

  • 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-2021-20237

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

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-2021-20237 updated cvss 5.9

zeromq: Memory leaks via metadata messages processed by PUB sockets

  • 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

1.69% chance of exploitation in the next 30 days, higher than 77% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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 Vulns 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.