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CVE-2021-20237

An uncontrolled resource consumption (memory leak) flaw was found in ZeroMQ's src/xpub.cpp in...

7.5 HighFix available

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.

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
None
Integrity
None
Availability
High

Exploit likelihood

1.69%Up 0.7 points since May 29, 2021
90%50%10%1%

What each source reports

NVD Score used 7.5

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.

Record
CVE-2021-20237
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0
4.3 MediumAV:N/AC:M/Au:N/C:N/I:N/A:P
Weakness
CWE-400, CWE-401
Updated
2026-11-02
CVE List No score

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.

Record
CVE-2021-20237
Weakness
CWE-400
Updated
2026-11-02
EUVDEUVD-2021-7676 No score

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.

Record
EUVD-2021-7676
Updated
2026-11-03
GitHub AdvisoriesGHSA-98wx-fq4r-jfm2 7.5

An uncontrolled resource consumption (memory leak) flaw was found in ZeroMQ's src/xpub.cpp in...

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.

Record
GHSA-98wx-fq4r-jfm2
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400, CWE-401
Updated
2026-11-02
OSV 7.5

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.

Record
CVE-2021-20237
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVDEBIAN-CVE-2021-20237 7.5

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.

Record
DEBIAN-CVE-2021-20237
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVJLSEC-2026-517 7.5

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.

Record
JLSEC-2026-517
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0
4.3 MediumAV:N/AC:M/Au:N/C:N/I:N/A:P
Updated
2026-11-02
OSVUBUNTU-CVE-2021-20237 7.5

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.

Record
UBUNTU-CVE-2021-20237
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVUSN-4920-1 No score

zeromq3 vulnerabilities

It was discovered that ZeroMQ incorrectly handled certain application metadata. A remote attacker could use this issue to cause ZeroMQ to crash, or possibly execute arbitrary code. (CVE-2019-13132)

It was discovered that ZeroMQ mishandled certain network traffic. An unauthenticated attacker could use this vulnerability to cause a denial-of- service and prevent legitimate clients from communicating with ZeroMQ. (CVE-2020-15166)

It was discovered that ZeroMQ did not properly manage memory under certain circumstances. If a user or automated system were tricked into connecting to one or multiple compromised servers, a remote attacker could use this issue to cause a denial of service. (CVE-2021-20234)

It was discovered that ZeroMQ incorrectly handled memory when processing messages with arbitrarily large sizes under certain circumstances. A remote unauthenticated attacker could use this issue to cause a ZeroMQ server to crash, resulting in a denial of service, or possibly execute arbitrary code. This issue only affected Ubuntu 18.04 ESM and Ubuntu 20.04 ESM. (CVE-2021-20235)

It was discovered that ZeroMQ did not properly manage memory under certain circumstances. A remote unauthenticated attacker could use this issue to cause a ZeroMQ server to crash, resulting in a denial of service. This issue only affected Ubuntu 18.04 ESM and Ubuntu 20.04 ESM. (CVE-2021-20237)

Record
USN-4920-1
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:18.04:LTS
before 4.2.5-1ubuntu0.2+esm2, plus listed versions
4.2.1-4ubuntu14.2.2-1ubuntu24.2.3-14.2.3-1build14.2.5-14.2.5-1ubuntu0.14.2.5-1ubuntu0.24.2.5-1ubuntu0.2+esm1
4.2.5-1ubuntu0.2+esm2
zeromq3
Ubuntu:Pro:20.04:LTS
before 4.3.2-2ubuntu1.20.04.1~esm2, plus listed versions
4.3.2-14.3.2-24.3.2-2ubuntu14.3.2-2ubuntu1.20.04.1~esm1
4.3.2-2ubuntu1.20.04.1~esm2
zeromq3
Ubuntu:Pro:14.04:LTS
From an advisory covering 5 CVEs
before 4.0.4+dfsg-2ubuntu0.1+esm3, plus listed versions
3.2.3+dfsg-23.2.4+dfsg-13.2.4+dfsg-23.2.4+dfsg-33.2.4+dfsg-4
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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+esm2
4.0.4+dfsg-2ubuntu0.1+esm3
zeromq3
Ubuntu:Pro:16.04:LTS
From an advisory covering 5 CVEs
before 4.1.4-7ubuntu0.1+esm2, 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+esm1
4.1.4-7ubuntu0.1+esm2
zeromq3
Ubuntu:Pro:18.04:LTS
From an advisory covering 5 CVEs
before 4.2.5-1ubuntu0.2+esm2, plus listed versions
4.2.1-4ubuntu14.2.2-1ubuntu24.2.3-14.2.3-1build14.2.5-14.2.5-1ubuntu0.14.2.5-1ubuntu0.24.2.5-1ubuntu0.2+esm1
4.2.5-1ubuntu0.2+esm2
zeromq3
Ubuntu:Pro:20.04:LTS
From an advisory covering 5 CVEs
before 4.3.2-2ubuntu1.20.04.1~esm2, plus listed versions
4.3.2-14.3.2-24.3.2-2ubuntu14.3.2-2ubuntu1.20.04.1~esm1
4.3.2-2ubuntu1.20.04.1~esm2

History

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

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

In short

CVE-2021-20237 is a high vulnerability (CVSS 7.5) 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 1.69%, the 77th percentile. Fixed in zeromq3 4.3.3-1.

References

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