CVE-2021-20237: Zeromq Libzmq

High severity, CVSS 7.5. EPSS: 1.7% chance of exploitation in the next 30 days.

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.

Affected products

• Zeromq Libzmq: from 4.2.0, before 4.3.3 (fixed in 4.3.3)

Published 2021-05-28. Last modified 2026-06-17.