HOMEVULNERABILITIESCVE-2021-20237
HIGH

CVE-2021-20237

CWE-400Published: May 28, 2021· Updated: Jun 17, 2026

7.5
CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2021-20237 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 availability disruption (denial of service), with a CVSS base score of 7.5.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityNone
IntegrityNone
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected Vendors & Products

zeromq1 product(s)
libzmq
Source: NVD CPE · 1 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
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Official Patches & Advisories

PATCHhttps://github.com/zeromq/libzmq/security/advisories/GHSA-4p5v-h92w-6wxw
PATCHhttps://github.com/zeromq/libzmq/security/advisories/GHSA-4p5v-h92w-6wxw
ADVISORYhttps://bugzilla.redhat.com/show_bug.cgi?id=1921989
ADVISORYhttps://bugzilla.redhat.com/show_bug.cgi?id=1921989

All References (4)

→
https://bugzilla.redhat.com/show_bug.cgi?id=1921989Issue Tracking · Third Party Advisory
→
https://github.com/zeromq/libzmq/security/advisories/GHSA-4p5v-h92w-6wxwPatch · Third Party Advisory
→
https://bugzilla.redhat.com/show_bug.cgi?id=1921989Issue Tracking · Third Party Advisory
→
https://github.com/zeromq/libzmq/security/advisories/GHSA-4p5v-h92w-6wxwPatch · Third Party Advisory

Quick Facts

CVE IDCVE-2021-20237
CVSS Score7.5 / 10
SeverityHIGH
WeaknessCWE-400
CISA KEVNo
Affected1 vendor(s)
PublishedMay 28, 2021

Related CVEs (CWE-400)

CVE-2018-16492
9.8
CVE-2018-16486
9.8
CVE-2018-16489
9.8
CVE-2018-16491
9.8
CVE-2015-4412
9.8
CVE-2018-19282
9.8

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-20237 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
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