Every CVE Search/ Get API key

CVE-2021-20236

A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious...

9.8 CriticalFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
High

Exploit likelihood

1.87%Up 1.2 points since May 29, 2021
90%50%10%1%

What each source reports

NVD Score used 9.8

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.

Record
CVE-2021-20236
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS 2.0
7.5 HighAV:N/AC:L/Au:N/C:P/I:P/A:P
Weakness
CWE-120, CWE-787
Updated
2026-11-02
CVE List No score

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.

Record
CVE-2021-20236
Weakness
CWE-120
Updated
2026-11-02
EUVDEUVD-2021-7675 No score

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.

Record
EUVD-2021-7675
Updated
2026-11-03
GitHub AdvisoriesGHSA-4j25-p3vq-p264 9.8

A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious...

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.

Record
GHSA-4j25-p3vq-p264
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-787
Updated
2026-11-02
OSVBELL-CVE-2021-20236 9.8

CVE-2021-20236 does not affect BellSoft software

Record
BELL-CVE-2021-20236
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSV 9.8

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.

Record
CVE-2021-20236
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVDEBIAN-CVE-2021-20236 9.8

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.

Record
DEBIAN-CVE-2021-20236
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVJLSEC-2026-516 9.8

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.

Record
JLSEC-2026-516
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS 2.0
7.5 HighAV:N/AC:L/Au:N/C:P/I:P/A:P
Updated
2026-11-02
OSVUBUNTU-CVE-2021-20236 9.8

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.

Record
UBUNTU-CVE-2021-20236
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
zeromq3
Debian:12
 before 4.3.3-1
4.3.3-1
zeromq3
Debian:13
 before 4.3.3-1
4.3.3-1
zeromq3
Debian:14
 before 4.3.3-1
4.3.3-1
ZeroMQ_jll
Julia
 before 4.3.4+0
4.3.4+0
zeromq3
Ubuntu:Pro:14.04:LTS
 All versions, plus listed versions
3.2.3+dfsg-23.2.4+dfsg-13.2.4+dfsg-23.2.4+dfsg-33.2.4+dfsg-4
Show 6 moreShow less
4.0.3+dfsg-14.0.4+dfsg-24.0.4+dfsg-2ubuntu0.14.0.4+dfsg-2ubuntu0.1+esm14.0.4+dfsg-2ubuntu0.1+esm24.0.4+dfsg-2ubuntu0.1+esm3
 None known
zeromq3
Ubuntu:Pro:16.04:LTS
 All versions, plus listed versions
4.0.5+dfsg-3ubuntu1~gcc5.14.0.5+dfsg-3ubuntu24.1.4-74.1.4-7ubuntu0.14.1.4-7ubuntu0.1+esm14.1.4-7ubuntu0.1+esm2
 None known
zeromq3
Ubuntu:Pro:18.04:LTS
 All versions, plus listed versions
4.2.1-4ubuntu14.2.2-1ubuntu24.2.3-14.2.3-1build14.2.5-1
Show 4 moreShow less
4.2.5-1ubuntu0.14.2.5-1ubuntu0.24.2.5-1ubuntu0.2+esm14.2.5-1ubuntu0.2+esm2
 None known
zeromq3
Ubuntu:Pro:20.04:LTS
 All versions, plus listed versions
4.3.2-14.3.2-24.3.2-2ubuntu14.3.2-2ubuntu1.20.04.1~esm14.3.2-2ubuntu1.20.04.1~esm2
 None known

History

History
RecordedChangedSources
aliases, productsEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-20236 is a critical vulnerability (CVSS 9.8) in Microsoft Zeromq, published May 28, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.87%, the 79th percentile. Fixed in zeromq3 4.3.3-1.

References

Pages All vulnerabilities Browse Docs Sources Guide Get API key
MoveEnter Open