Security readout for executives and security teams
Plain-English summary
Some Mosquitto MQTT brokers could unintentionally allow access if administrators configured an ACL file that was empty or only comments. Instead of denying access, affected versions treated it like no ACL file existed and used a default allow policy.
Executive priority
Treat as a configuration-dependent access-control issue. Prioritize internet-facing or operational MQTT brokers carrying sensitive telemetry, device control, or customer data. Urgency is lower where Mosquitto is updated or ACL files are populated and verified.
Technical view
CVE-2018-12550 affects Eclipse Mosquitto 1.0 through 1.5.5 when acl_file is configured but contains no effective ACL entries. The broker interpreted that state as no ACL file and allowed access by default. The corrected behavior is to deny all access for an empty ACL file.
Likely exposure
Exposure is limited to Mosquitto 1.0-1.5.5 deployments that use ACL-file authorization and have an empty, blank-only, or comment-only ACL file. Systems without that configuration are not shown as affected by the provided sources.
Exploitation context
The source bundle does not report active exploitation, and CISA KEV status is false. Risk comes from misconfiguration-driven authorization bypass: clients may access MQTT resources administrators expected the ACL file to restrict.
Researcher notes
No CVSS score is provided in the bundle. The affected condition is narrow but security-relevant because an expected deny policy became allow-by-default. Evidence supports version range, configuration trigger, and corrected behavior, but not exploit prevalence.
Mitigation direction
- Update Mosquitto using vendor or distribution security guidance.
- Apply Debian DLA 1972-1 where relevant to Debian LTS systems.
- Ensure configured ACL files contain explicit, intended access rules.
- Avoid deploying empty or comment-only ACL files in production.
- Review broker authorization defaults after package updates.
Validation and detection
- Inventory Mosquitto versions and identify systems running 1.0 through 1.5.5.
- Check broker configuration for acl_file usage.
- Review ACL files for effective non-comment rules.
- Confirm empty ACL files deny access after remediation.
- Document any broker intentionally operating without ACL authorization.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
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ATT&CK lookup starting points
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Open ATT&CK lookupCVE-2018-12550 mapping review
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Open ATT&CK lookup- Severity
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS and timeline data
No CVSS vectors or timeline events were available in the normalized CVE source material.
Source materials
- CVE List V5 sourceCVE List V5
- https://bugs.eclipse.org/bugs/show_bug.cgi?id=541870CVE reference · x_refsource_CONFIRM
- [debian-lts-announce] 20191026 [SECURITY] [DLA 1972-1] mosquitto security updateCVE reference · mailing-list, x_refsource_MLIST
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Expected Behavior Violation
Expected Behavior Violation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.