Is CVE-2021-20235 actively exploited?

No active exploitation of CVE-2021-20235 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2021-20235 be exploited remotely?

Yes. CVE-2021-20235 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2021-20235?

CVE-2021-20235 has a CVSS score of 8.1 (HIGH).

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HIGH

CVE-2021-20235

CWE-120Published: April 1, 2021· Updated: Jun 17, 2026

8.1

CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2021-20235 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 8.1.