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Fencer Vulns
medium 6.5

CVE-2021-28166 json

In Eclipse Mosquitto version 2.0.0 to 2.0.9, if an authenticated client that had connected with MQTT v5 sent a crafted CONNACK message to t…

published 2021-04-07 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-14859

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.0%
EPSS 1.0% chance of exploitation in 30 days, percentile 62%
public exploits
0
none known

Summary

In Eclipse Mosquitto version 2.0.0 to 2.0.9, if an authenticated client that had connected with MQTT v5 sent a crafted CONNACK message to the broker, a NULL pointer dereference would occur.

Patch / fix

  • mosquitto Debian 14, Debian 13, Debian 12 2.0.10-1

debian advisories DEBIAN-CVE-2021-28166

  • mosquitto Alpine 3.24, Alpine 3.23, Alpine 3.22 +8 more 2.0.10-r0

alpine advisories ALPINE-CVE-2021-28166

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • mosquitto Arch Linux 2.0.10-1

arch linux advisories AVG-1793

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-28166 updated cvss 6.5

mosquitto: crafted CONNACK message to the broker leads to null pointer dereference

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.97% chance of exploitation in the next 30 days, higher than 62% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H/E:F/RL:O/RC:C
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 4.0 AV:N/AC:L/Au:S/C:N/I:N/A:P

Affected products

  • The Eclipse Foundation Eclipse Mosquitto

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.