Security readout for executives and security teams
Plain-English summary
Mattermost Server versions before 5.2 and 5.1.1 had an authorization bypass. A crafted mismatch between a channel name in request parameters and the request body could let access checks make the wrong decision. The source bundle does not provide severity, CVSS, or impact detail.
Executive priority
Treat this as a targeted legacy-platform risk. If Mattermost is still below the fixed versions, schedule remediation promptly because authorization bypasses can expose restricted collaboration content.
Technical view
The flaw is an authorization inconsistency in Mattermost Server. When the channel name differed between params and body, authorization could be bypassed. The record names affected versions only as Mattermost Server before 5.2 and 5.1.1, with no CWE, CVSS vector, or detailed endpoint scope provided.
Likely exposure
Exposure is likely limited to organizations still running Mattermost Server versions older than 5.2 or the 5.1.1 maintenance release. Current installations are unlikely to be affected if they have followed Mattermost security updates.
Exploitation context
The bundle does not cite active exploitation, public exploit activity, or CISA KEV listing. The available evidence supports a potential authorization bypass, not confirmed in-the-wild exploitation.
Researcher notes
Evidence is sparse. The CVE description identifies the condition but not endpoint names, exploit prerequisites, privileges required, or data impact. Avoid assuming exploitability beyond the parameter/body channel-name mismatch described.
Mitigation direction
- Upgrade Mattermost Server to 5.2, 5.1.1, or a later supported release.
- Review Mattermost security updates for any version-specific guidance.
- Retire or isolate unsupported legacy Mattermost deployments.
- Prioritize externally reachable or high-sensitivity Mattermost workspaces first.
Validation and detection
- Inventory all Mattermost Server instances and record exact versions.
- Confirm no instance runs a version before 5.2 or 5.1.1.
- Review access-control logs for unusual channel access patterns.
- Check change records for completion of Mattermost security updates.
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
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CVE-2018-21251 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
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://mattermost.com/security-updates/CVE reference · x_refsource_CONFIRM
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.