CVE-2021-33176Network attack vector

Broker crash via unbounded topic depth

Published Jun 8, 2021 · Updated Aug 3, 2024

Resource exhaustion in Octavo Labs VerneMQ before 1.12.0 allows remote attackers to crash the broker with deeply nested MQTT topics. MQTT topic handling accepts unbounded topic levels and allocates memory while processing attacker-controlled topic strings until the operating system terminates the process. No prior privileges or user interaction are required when an MQTT listener is reachable; the documented consequence is interruption of broker service.

CVSS severity7.5
High
EPSS probability1.10%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Octavo Labs VerneMQ before 1.12.0 allows remote attackers to crash the broker with deeply nested MQTT topics. MQTT topic handling accepts unbounded topic levels and allocates memory while processing attacker-controlled topic strings until the operating system terminates the process. No prior privileges or user interaction are required when an MQTT listener is reachable; the documented consequence is interruption of broker service.

The record

CVE
CVE-2021-33176
Published
Jun 8, 2021
Updated
Aug 3, 2024
Vendor
Octavo Labs
Product
VerneMQ
Classifications
CWE-502, CWE-770, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=<1.12.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Octavo Labs · VerneMQversion=<1.12.0

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
CWE-770Allocation of Resources Without Limits or Throttling
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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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