CVE-2018-12550
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 · uneditedWhen Eclipse Mosquitto version 1.0 to 1.5.5 (inclusive) is configured to use an ACL file, and that ACL file is empty, or contains only comments or blank lines, then Mosquitto will treat this as though no ACL file has been defined and use a default allow policy. The new behaviour is to have an empty ACL file mean that all access is denied, which is not a useful configuration but is not unexpected.
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 confidenceIn Eclipse Mosquitto versions 1.0-1.5.5, when an ACL file is configured but contains only comments, blank lines, or is empty, Mosquitto incorrectly applies a default ALLOW policy rather than restricting access. This occurs because the empty ACL is treated as if no ACL file exists, allowing all clients full access to all topics despite the administrator's intent to implement access control.
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>= 1.0, <= 1.5.5CVSS 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
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
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 checksWork through these to decide whether this CVE applies to you.
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Check Mosquitto versionRun `mosquitto --version` or check via package manager (`dpkg -l | grep mosquitto` on Debian/Ubuntu, `rpm -qi mosquitto` on RHEL/CentOS)Affected if Version is 1.0 through 1.5.5 inclusive
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Locate the Mosquitto configuration fileCommon locations are /etc/mosquitto/mosquitto.conf or /etc/mosquitto/conf.d/. Check the -c flag if mosquitto runs with custom configAffected if Configuration file exists and is readable
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Identify ACL file configurationIn mosquitto.conf, search for the `acl_file` directive and note the path it points toAffected if An acl_file directive is present and points to a file path
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Examine ACL file contentsRead the ACL file using `cat <path>` or `cat <path> | grep -v '^#' | grep -v '^$'`. Check if file contains only comments, blank lines, or is completely emptyAffected if ACL file exists but contains no actual allow or deny rules (only comments, blank lines, or is empty)
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Verify client access behaviorAttempt to connect a test client and publish/subscribe to a topic that would normally be restricted. With the bug, access will be granted despite empty ACLAffected if Clients can publish/subscribe to any topic when ACL file is configured but empty
You are affected if Mosquitto version is between 1.0 and 1.5.5 AND an ACL file is configured but contains only comments, blank lines, or is empty, resulting in unintended full access.
Generated from the published advisory. Verify against your own configuration.
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.
From vendor dataUpgrade Mosquitto to version 1.5.6 or later, which correctly treats empty ACL files as denying all access. Alternatively, ensure all ACL files contain explicit allow/deny rules and validate that access control is functioning as intended.
- Consultation2.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2018-12550 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2018-12550 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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