How severe is CVE-2021-20234?

CVE-2021-20234 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-20234 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (64th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-20234?

CVE-2021-20234 affects Zeromq Libzmq. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-20234?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-20234 published?

CVE-2021-20234 was published on 2021-04-01 and last updated on 2026-06-17.

CVE-2021-20234

CVE-2021-20234 is a medium-severity vulnerability in Zeromq Libzmq with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-401.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
CVSS v2: 4.3
EPSS exploit prediction: 1% (64th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-401
Affected product: Zeromq Libzmq
Published: 2021-04-01
Last modified: 2026-06-17

Description

An uncontrolled resource consumption (memory leak) flaw was found in the ZeroMQ client in versions before 4.3.3 in src/pipe.cpp. This issue causes a client that connects to multiple malicious or compromised servers to crash. The highest threat from this vulnerability is to system availability.

Frequently asked questions

What is CVE-2021-20234?: An uncontrolled resource consumption (memory leak) flaw was found in the ZeroMQ client in versions before 4.3.3 in src/pipe.cpp. This issue causes a client that connects to multiple malicious or compromised servers to crash. The highest threat from this vulnerability is to system availability.
How severe is CVE-2021-20234?: CVE-2021-20234 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-20234 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (64th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-20234?: CVE-2021-20234 affects Zeromq Libzmq. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-20234?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-20234 published?: CVE-2021-20234 was published on 2021-04-01 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:zeromq:libzmq:*:*:*:*:*:*:*:*

More vulnerabilities in Zeromq Libzmq

CVE-2020-36400 — Critical (CVSS 9.8): ZeroMQ libzmq 4.3.3 has a heap-based buffer overflow in zmq::tcp_read, a different vulnerability than CVE-2021-20235.
CVE-2019-13132 — Critical (CVSS 9.8): In ZeroMQ libzmq before 4.0.9, 4.1.x before 4.1.7, and 4.2.x before 4.3.2, a remote, unauthenticated client connecting…
CVE-2019-6250 — High (CVSS 8.8): A pointer overflow, with code execution, was discovered in ZeroMQ libzmq (aka 0MQ) 4.2.x and 4.3.x before 4.3.1. A…
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CVE-2021-20237 — High (CVSS 7.5): An uncontrolled resource consumption (memory leak) flaw was found in ZeroMQ's src/xpub.cpp in versions before 4.3.3.…
CVE-2020-15166 — High (CVSS 7.5): In ZeroMQ before version 4.3.3, there is a denial-of-service vulnerability. Users with TCP transport public endpoints,…

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