What is CVE-2021-34434?

CVE-2021-34434 is a medium-severity vulnerability in Eclipse Mosquitto, classified under Improper Authorization. CVSS score: 5.3/10. Published 2021-08-30.

How severe is CVE-2021-34434?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Auth bypass in Eclipse Mosquitto

CVE-2021-34434

In Eclipse Mosquitto versions 2.0 to 2.0.11, when using the dynamic security plugin, if the ability for a client to make subscriptions on a topic is revoked when a durable client is offline, then existing subscriptions for that client are not revoked.

Published 2021-08-30 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.013 (70.0th percentile), scored 2026-10-01.

Low probability of exploitation in the next 30 days, but still tracked. 70th percentile — 70.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.014 · newest: 0.013 · change: -0.000

Affected products

Eclipse Mosquitto
The Eclipse Foundation Mosquitto — versions 2.0, unspecified
Fedoraproject Fedora — versions 34, 35

Weakness classification (CWE)

References

bugs.eclipse.org/bugs/show_bug.cgi (Exploit, Issue Tracking, Vendor Advisory)
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)
www.debian.org/security/2023/dsa-5511 (vendor-advisory)

Frequently asked questions

What is CVE-2021-34434?: CVE-2021-34434 is a medium-severity vulnerability in Eclipse Mosquitto, classified under Improper Authorization. CVSS score: 5.3/10. Published 2021-08-30.
How severe is CVE-2021-34434?: Medium severity. CVSS v3 base score is 5.3 out of 10.