dbcve.org
Rabbitmq ServerApplication · Broadcom

CVE-2026-44838

HIGH · 8.1 CVSS v3.1 Published 2026-05-27
Fix available
A fix is available. Upgrade to 4.2.4 or later.
See remediation →
87/100
Remediation priority · High
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
RabbitMQ is a messaging and streaming broker. From 4.2.0 to before 4.2.4, RabbitMQ's MQTT plugin allows for topic-level authorization using regular expressions with variable substitution. Administrators can create patterns such as ^{client_id}-sensors$ to restrict user access to topics that include their client ID. However, the client_id is provided by the user in the MQTT CONNECT packet and is inserted into the regex pattern without escaping special regex characters. This flaw enables an authenticated MQTT user to inject regex operators to bypass authorization. This vulnerability is fixed in 4.2.4 and 4.3.0.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

In RabbitMQ MQTT plugin versions 4.2.0 through 4.2.3, the client_id from the MQTT CONNECT packet is inserted directly into regex authorization patterns without escaping special regex metacharacters. This allows an authenticated MQTT user to inject regex operators (like .*, +, ?) in their client_id to bypass topic-level authorization restrictions and access topics outside their intended scope.

MitigationUpgrade RabbitMQ to version 4.2.4 or 4.3.0 where the client_id is properly escaped before insertion into regex patterns. Until patched, avoid using client_id variable substitution in MQTT topic authorization regex patterns.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Rabbitmq ServerApplication
Affected:>= 4.2.0, < 4.2.4

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check RabbitMQ server version
    Run 'rabbitmqctl status' or check the RabbitMQ log file at /var/log/rabbitmq/[email protected] for the version string
    Affected if Version is 4.2.0, 4.2.1, 4.2.2, or 4.2.3 (versions >= 4.2.0 and < 4.2.4 are affected)
  2. Verify MQTT plugin is enabled
    Run 'rabbitmq-plugins list' and look for 'rabbitmq_mqtt' in the enabled list, or check rabbitmq.conf for 'mqtt.default_vhost' configuration
    Affected if The MQTT plugin is enabled and the server is using MQTT connections
  3. Examine MQTT topic authorization configuration
    Check rabbitmq.conf or the relevant authorization configuration file for MQTT-specific authorization rules. Look for 'mqtt.topic_access' or similar MQTT authorization settings that use the client_id variable in regex patterns
    Affected if MQTT topic authorization rules use client_id variable substitution (such as #{client_id}) within regex pattern definitions

The environment is affected only if RabbitMQ version is 4.2.0-4.2.3, the MQTT plugin is enabled, AND MQTT topic authorization rules incorporate the client_id variable in regex patterns for access control.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 4.2.4 or later
Fixed in 4.2.4
Interim mitigation

Upgrade RabbitMQ to version 4.2.4 or 4.3.0 where the client_id is properly escaped before insertion into regex patterns. Until patched, avoid using client_id variable substitution in MQTT topic authorization regex patterns.

Recommended fix High confidence

RabbitMQ Server 4.2.4 or 4.3.0

  1. Backup your RabbitMQ configuration, data directory, and any custom definitions (definitions.json) before upgrading
  2. Schedule a maintenance window as upgrade requires a brief broker restart
  3. Stop the RabbitMQ service or application gracefully to ensure all connections are drained
  4. Upgrade RabbitMQ Server to version 4.2.4 (or 4.3.0 for the newer major release) using your package manager or installation method (e.g., yum/apt upgrade rabbitmq-server, or manual package installation)
  5. Start the upgraded RabbitMQ service
  6. Verify the MQTT plugin is loaded and functioning: run `rabbitmq-plugins list` to confirm mqtt plugin is enabled, then test MQTT connections
  7. Review RabbitMQ logs (typically in /var/log/rabbitmq/ or the configured log directory) for any errors during startup
  8. If using topic authorization with client_id regex patterns, test that the fix properly escapes special regex characters in the client_id variable substitution
Caveat Review release notes for 4.2.4 and 4.3.0 for any migration notes; ensure client applications are compatible with the MQTT plugin changes in these versions

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Rabbitmq Server Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,210
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-44838 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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