CVE-2021-34431Network attack vector

Broker memory exhaustion via crafted CONNECT

Published Jul 22, 2021 · Updated Aug 4, 2024

Memory leak in Eclipse Mosquitto 1.6 through 2.0.10 allows remote authenticated users to cause broker DoS via MQTT v5 CONNECT. The broker's MQTT v5 CONNECT parser fails to release memory when processing a crafted CONNECT message, allowing repeated requests to accumulate allocations. Exploitation requires an authenticated client able to connect with MQTT v5; sustained leakage can exhaust broker memory and interrupt service.

CVSS severity6.5
Medium
EPSS probability1.11%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory leak in Eclipse Mosquitto 1.6 through 2.0.10 allows remote authenticated users to cause broker DoS via MQTT v5 CONNECT. The broker's MQTT v5 CONNECT parser fails to release memory when processing a crafted CONNECT message, allowing repeated requests to accumulate allocations. Exploitation requires an authenticated client able to connect with MQTT v5; sustained leakage can exhaust broker memory and interrupt service.

The record

CVE
CVE-2021-34431
Published
Jul 22, 2021
Updated
Aug 4, 2024
Vendor
The Eclipse Foundation
Product
Eclipse Mosquitto
Classifications
CWE-401, T1499
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.6 <unspecified
  2. Affected versionversion=unspecified <=2.0.10

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

The Eclipse Foundation · Eclipse Mosquittoversion=1.6 <unspecified; version=unspecified <=2.0.10

Published CVSS scores

6.5NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.0NVDAV:N/AC:L/Au:S/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-401Missing Release of Memory after Effective Lifetime
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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