HOMEVULNERABILITIESCVE-2021-20236
CRITICAL

CVE-2021-20236

CWE-120Published: May 28, 2021· Updated: Jun 17, 2026

9.8
CVSS v3.1

Official Description

A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.

NVD Source

Technical Analysis

CVE-2021-20236 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 9.8.

CVSS v3.1 Vector Breakdown

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

Affected Vendors & Products

Fedora1 product(s)
fedora
Red Hat2 product(s)
ceph storageenterprise linux
zeromq1 product(s)
zeromq
Source: NVD CPE · 4 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-qq65-x72m-9wr8
PATCHhttps://github.com/zeromq/libzmq/security/advisories/GHSA-qq65-x72m-9wr8
ADVISORYhttps://bugzilla.redhat.com/show_bug.cgi?id=1921976
ADVISORYhttps://bugzilla.redhat.com/show_bug.cgi?id=1921976

All References (4)

→
https://bugzilla.redhat.com/show_bug.cgi?id=1921976Issue Tracking · Third Party Advisory
→
https://github.com/zeromq/libzmq/security/advisories/GHSA-qq65-x72m-9wr8Patch · Third Party Advisory
→
https://bugzilla.redhat.com/show_bug.cgi?id=1921976Issue Tracking · Third Party Advisory
→
https://github.com/zeromq/libzmq/security/advisories/GHSA-qq65-x72m-9wr8Patch · Third Party Advisory

Quick Facts

CVE IDCVE-2021-20236
CVSS Score9.8 / 10
SeverityCRITICAL
WeaknessCWE-120
CISA KEVNo
Affected3 vendor(s)
PublishedMay 28, 2021

Related CVEs (CWE-120)

CVE-2012-10035
10.0
CVE-2002-1337
10.0
CVE-2021-33975
10.0
CVE-2021-33972
10.0
CVE-2017-16740
10.0
CVE-2010-10016
10.0

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-20236 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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