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Fencer Vulns
high 8.1

CVE-2021-20235 in the critical feed json

There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp.

published 2021-04-01 5 y ago modified 2026-07-25 3 mo ago also EUVD-2021-7674 , JLSEC-2026-515

cvss
8.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
43.9%
EPSS 43.9% chance of exploitation in 30 days, percentile 98%
public exploits
0
none known

Summary

There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp. The decoder static allocator could have its sized changed, but the buffer would remain the same as it is a static buffer. A remote, unauthenticated attacker who sends a crafted request to the zeromq server could trigger a buffer overflow WRITE of arbitrary data if CURVE/ZAP authentication is not enabled. The greatest impact of this flaw is to application availability, data integrity, and confidentiality.

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-2021-20235

  • 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-2021-20235

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-2021-20235 updated cvss 8.1

zeromq: Heap overflow when receiving malformed ZMTP v1 packets

  • 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

43.86% chance of exploitation in the next 30 days, higher than 98% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P
OSV 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/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-120 Buffer Copy without Checking Size of Input
  • CWE-787 Out-of-bounds Write

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.