CVE-2021-34432Public exploitNetwork attack vector

Broker crash via unchecked null publish topic

Published Jul 27, 2021 · Updated Jul 2, 2026

Denial of service in Eclipse Mosquitto 2.0.7 and earlier allows remote attackers to crash the broker with a zero-length PUBLISH topic. The broker passes the resulting null topic pointer to mosquitto_pub_topic_check(), which accepts it instead of returning MOSQ_ERR_INVAL. Unauthenticated network access to an MQTT listener is sufficient; the demonstrated consequence is broker termination without reported data disclosure or modification.

CVSS severity7.5
High
EPSS probability1.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Eclipse Mosquitto 2.0.7 and earlier allows remote attackers to crash the broker with a zero-length PUBLISH topic. The broker passes the resulting null topic pointer to mosquitto_pub_topic_check(), which accepts it instead of returning MOSQ_ERR_INVAL. Unauthenticated network access to an MQTT listener is sufficient; the demonstrated consequence is broker termination without reported data disclosure or modification.

The record

CVE
CVE-2021-34432
Published
Jul 27, 2021
Updated
Jul 2, 2026
Vendor
The Eclipse Foundation
Product
Eclipse Mosquitto
Classifications
CWE-20, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 27, 2021CVE publishedPublication date reported by the CVE source.
  2. Jul 2, 2026Record 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=unspecified <=2.0.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Eclipse Foundation · Eclipse Mosquittoversion=unspecified <=2.0.7

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV:N/AC:L/Au:N/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-20Improper Input Validation
T1499Endpoint Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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