Security readout for executives and security teams
Plain-English summary
This flaw could let someone invite a user who should not be permitted into a Mattermost Server workspace. The main business concern is unauthorized access expansion, especially in private collaboration environments. The source bundle does not provide CVSS scoring or impact detail beyond the invitation bypass.
Executive priority
Treat this as a targeted access-control issue for Mattermost environments. Prioritize remediation where Mattermost hosts sensitive internal discussions, customer data, security operations, or restricted collaboration channels. Urgency is hard to score because public severity and exploitation evidence are incomplete.
Technical view
Mattermost Server before 5.1, 5.0.2, and 4.10.2 allowed an attacker to use the invite_people slash command to invite a non-permitted user. The available sources do not provide CWE classification, CVSS metrics, exploit prerequisites, or deeper technical root cause.
Likely exposure
Exposure is limited to Mattermost Server deployments running versions before 5.1, 5.0.2, or 4.10.2. The source bundle lists no CPEs and does not clarify whether all deployment modes or configurations are affected.
Exploitation context
The provided sources do not state active exploitation, and the KEV flag is false. Public evidence only confirms the possibility of inviting a non-permitted user through the invite_people slash command.
Researcher notes
The source bundle is sparse. It confirms affected version boundaries and the invite_people behavior, but not authentication level, tenant impact, CVSS, CWE, exploit availability, or fixed commit details. Avoid expanding claims beyond unauthorized invitation of non-permitted users.
Mitigation direction
- Upgrade Mattermost Server to 5.1, 5.0.2, 4.10.2, or later.
- Review Mattermost security updates for version-specific vendor guidance.
- Restrict invitation privileges until affected instances are upgraded.
- Audit workspace membership for unexpected or unauthorized users.
Validation and detection
- Confirm the deployed Mattermost Server version.
- Check whether any instance is older than 5.1, 5.0.2, or 4.10.2.
- Review logs for invite_people command usage around sensitive workspaces.
- Verify invitation controls block non-permitted user invitations after remediation.
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-2018-21253 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.