Security readout for executives and security teams
Plain-English summary
Older Mattermost Server versions may send intra-team posts to users who should not receive them under the flags API permission model. The business risk is unintended internal information exposure, especially where Mattermost carries sensitive operational, security, or customer discussions.
Executive priority
Treat as a privacy and internal communications exposure issue, not a confirmed emergency. Prioritize remediation where Mattermost contains sensitive business, customer, legal, or security discussions.
Technical view
CVE-2019-20887 is an access-control issue in Mattermost Server before 5.7.1, 5.6.4, 5.5.3, and 4.10.6. The server does not honor flags API permissions when deciding whether a user can receive intra-team posts. Public source data provides no CVSS score or CWE.
Likely exposure
Exposure is likely limited to organizations running affected Mattermost Server versions before 5.7.1, 5.6.4, 5.5.3, or 4.10.6. Cloud, deployment-specific, and configuration-specific exposure is not described in the supplied sources.
Exploitation context
The supplied sources do not report active exploitation, and this CVE is not marked as CISA KEV. Evidence is insufficient to claim public exploitation or weaponized tooling.
Researcher notes
The record lacks CVSS, CWE, exploit detail, and affected CPEs. Analysis should stay focused on the stated permission-check failure and fixed version boundaries. Avoid assuming broader message disclosure beyond intra-team posts.
Mitigation direction
- Inventory Mattermost Server versions across all environments.
- Upgrade to a fixed or currently supported Mattermost Server release.
- Review Mattermost security updates for version-specific guidance.
- Restrict Mattermost access where immediate upgrade is not possible.
- Review channel and team permission settings after upgrading.
Validation and detection
- Confirm no production instance runs below the fixed version thresholds.
- Verify permission-sensitive intra-team post delivery in staging.
- Review audit logs for unexpected message delivery or permission anomalies.
- Confirm Mattermost security advisories are tracked in vulnerability management.
- Document remediation status for each Mattermost deployment.
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-2019-20887 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.