CVE-2021-20235

Severity: high (CVSS 8.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 43.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-04-01 · updated 2026-06-17
Weakness: CWE-120

Description

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.

Affected products

zeromq libzmq: from 4.2.0 before 4.3.3 — fixed in 4.3.3

How to fix

Upgrade to a fixed version: zeromq libzmq 4.3.3. Check the vendor advisory for mitigations.

References

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