CVE-2014-9721: libzmq before 4.0.6 and 4.1.x before 4.1.1 allows remote attackers to conduct downgrade attacks and bypass ZMT

Q: How do I fix CVE-2014-9721?

zeromq: upgrade to newer than 4.0.5. Exact commands for each OS are on this page.

Q: Is CVE-2014-9721 being exploited?

CVE-2014-9721 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2014-9721 affect?

CVE-2014-9721 affects zeromq. Severity is medium (CVSS 4.3). libzmq before 4.0.6 and 4.1.x before 4.1.1 allows remote attackers to conduct downgrade attacks and bypass ZMTP v3 protocol security mechanisms via a ZMTP v2 or earlier header.

Q: How urgent is CVE-2014-9721?

Priority 36/100. No elevated risk signals yet.

Routine

MEDIUM 4.3UPGRADE

CVE-2014-9721 is a medium-severity flaw (CVSS 4.3) affecting zeromq. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

libzmq before 4.0.6 and 4.1.x before 4.1.1 allows remote attackers to conduct downgrade attacks and bypass ZMTP v3 protocol security mechanisms via a ZMTP v2 or earlier header.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
EPSS exploit chance	2.5% (top 15%)
CISA exploited list	No
Weakness	CWE-20
Published	2015-06-03
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: zeromq

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2015-06-03 20:59 UTCPublished CVE record published
2026-06-17 00:18 UTCUpdated Record last modified

zeromq zeromq UPGRADE

Affected: <= 4.0.5 · 4.1.0 rc1

Fixed in: newer than 4.0.5

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy zeromq || rpm -q zeromq || zeromq --version

2. UPGRADE to newer than 4.0.5 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade zeromq

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade zeromq

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2014-9721?

zeromq: upgrade to newer than 4.0.5. Exact commands for each OS are on this page.

Is CVE-2014-9721 being exploited?

CVE-2014-9721 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2014-9721 affect?

CVE-2014-9721 affects zeromq. Severity is medium (CVSS 4.3). libzmq before 4.0.6 and 4.1.x before 4.1.1 allows remote attackers to conduct downgrade attacks and bypass ZMTP v3 protocol security mechanisms via a ZMTP v2 or earlier header.

How urgent is CVE-2014-9721?

Priority 36/100. No elevated risk signals yet.

Related CVEs

CVE-2021-20236 CRITICAL 9.8 UPGRADE DOWNGRADE A flaw was found in the ZeroMQ server in versions before 4.3.3
CVE-2014-7203 MEDIUM 4.3 DOWNGRADE libzmq (aka ZeroMQ/C++) 4.0.x before 4.0.5 does not ensure that nonces are unique, which allows man-in-the-mid
CVE-2014-7202 MEDIUM 4.3 DOWNGRADE stream_engine.cpp in libzmq (aka ZeroMQ/C++)) 4.0.5 before 4.0.5 allows man-in-the-middle attackers to conduct

References

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