# CVE-2021-34431: libmosquitto1: In Eclipse Mosquitto version 1.6 to 2.0.10, if an authenticated client that had connected with MQTT v5 sent a crafted...

CVE-2021-34431 is fixed in 4 products on 1 platform, first by libmosquitto1 1.6.9-1ubuntu0.1~esm1, released October 2, 2023. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-34431
- Priority: Routine
- CVSS: n/a (Medium)
- EPSS: 0.0111
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 22, 2021

## Description

In Eclipse Mosquitto version 1.6 to 2.0.10, if an authenticated client that had connected with MQTT v5 sent a crafted CONNECT message to the broker a memory leak would occur, which could be used to provide a DoS attack against the broker.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libmosquitto1 Ubuntu 20.04 LTS (focal) | 1.6.9-1ubuntu0.1~esm1 | [libmosquitto1 1.6.9-1ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libmosquitto1-1.6.9-1ubuntu0.1-esm1.md) | Oct 2, 2023 |
| Linux | libmosquittopp1 Ubuntu 20.04 LTS (focal) | 1.6.9-1ubuntu0.1~esm1 | [libmosquittopp1 1.6.9-1ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libmosquittopp1-1.6.9-1ubuntu0.1-esm1.md) | Oct 2, 2023 |
| Linux | mosquitto Ubuntu 20.04 LTS (focal) | 1.6.9-1ubuntu0.1~esm1 | [mosquitto 1.6.9-1ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-mosquitto-1.6.9-1ubuntu0.1-esm1.md) | Oct 2, 2023 |
| Linux | mosquitto-clients Ubuntu 20.04 LTS (focal) | 1.6.9-1ubuntu0.1~esm1 | [mosquitto-clients 1.6.9-1ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-mosquitto-clients-1.6.9-1ubuntu0.1-esm1.md) | Oct 2, 2023 |

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Data as of 2026-11-09T13:31:49Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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