How severe is CVE-2021-20237?

CVE-2021-20237 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-20237 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-20237?

CVE-2021-20237 affects Zeromq Libzmq. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-20237?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-20237 published?

CVE-2021-20237 was published on 2021-05-28 and last updated on 2026-06-17.

CVE-2021-20237

CVE-2021-20237 is a high-severity vulnerability in Zeromq Libzmq with a CVSS 3.x base score of 7.5. 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: High (CVSS 3.x base score 7.5)
CVSS v2: 4.3
EPSS exploit prediction: 2% (74th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-401
Affected product: Zeromq Libzmq
Published: 2021-05-28
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2021-20237?: 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.
How severe is CVE-2021-20237?: CVE-2021-20237 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-20237 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-20237?: CVE-2021-20237 affects Zeromq Libzmq. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-20237?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-20237 published?: CVE-2021-20237 was published on 2021-05-28 and last updated on 2026-06-17.

References

Affected products (1)

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

More vulnerabilities in Zeromq Libzmq

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