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Vulnerability record · CVE-2021-20236 · published 28 May 2021

CVE-2021-20236: Zeromq classic buffer overflow vulnerability

Zeromq · Zeromq

A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.

9.8 CVSS 3.1 Critical EPSS 1.6% · top 25.2% CWE-120 · Classic buffer overflowCWE-787 · Out-of-bounds write
9.8CVSS 3.1 base score, v2 7.5
1.6%EPSS exploitation probability, 30 days
NoNot in CISA KEV
4Affected product versions listed by NVD
4References
17 Jun 2026Last modified by NVD

Description

A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

4 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://bugzilla.redhat.com/show_bug.cgi?id=1921976 Issue TrackingThird Party Advisory
https://github.com/zeromq/libzmq/security/advisories/GHSA-qq65-x72m-9wr8 PatchThird Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1921976 Issue TrackingThird Party Advisory
https://github.com/zeromq/libzmq/security/advisories/GHSA-qq65-x72m-9wr8 PatchThird Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2021-20236), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.