Connected Workspaces: Malicious remote server can manipulate arbitrary user's status
Priority LOW 13CWE-862Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- High
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Security bypass
- Confidentiality · integrity · availability
- None · Low · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-862.
Summary
Mattermost versions 10.11.x <= 10.11.12 fail to validate whether users were correctly owned by the correct Connected Workspace which allows a malicious remote server connected using the Conntexted Workspaces feature to change the displayed status of local users via the Connected Workspaces API.. Mattermost Advisory ID: MMSA-2026-00603
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00167 6th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 11.5.0, 10.11.13github.com/mattermost/mattermost-server (Go): 8.0.0-20260316060126-bc1a2b34b1f9
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Mattermost | Mattermost | 10.11.0 – 10.11.12 | 11.5.0, 10.11.13 | Patch available | CNA |
| — | github.com/mattermost/mattermost-server (Go) | 8.0.0-20250721062209-4952acea88ce to before 8.0.0-20260316060126-bc1a2b34b1f9 | 8.0.0-20260316060126-bc1a2b34b1f9 | Patch available | GHSA-mxxh-fmjq-j6x4 |
- Mattermost VendorMattermost Affected 10.11.0 – 10.11.12 Fixed in 11.5.0, 10.11.13 Patch available CNA
- github.com/mattermost/mattermost-server (Go) Vendor— Affected 8.0.0-20250721062209-4952acea88ce to before 8.0.0-20260316060126-bc1a2b34b1f9 Fixed in 8.0.0-20260316060126-bc1a2b34b1f9 Patch available GHSA-mxxh-fmjq-j6x4
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* | 10.11.0 to before 10.11.13 | Vulnerable | Mattermost |
- cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* Versions 10.11.0 to before 10.11.13 Vulnerable ·Mattermost
Remediation
- Fix · CNA Mattermost (Mattermost) Fixed in 11.5.0, 10.11.13
- Fix · GHSA-mxxh-fmjq-j6x4 github.com/mattermost/mattermost-server (Go) Fixed in 8.0.0-20260316060126-bc1a2b34b1f9 Advisory →
Vendor assessments
Timeline
- 2026-10-02 Threatist record created from CVE-2026-27769
- 2026-10-03 Alias added: GHSA-mxxh-fmjq-j6x4
References
More Mattermost Server vulnerabilities
- TI-2025-18933 Arbitrary file read in Mattermost Boards via import & export board archive CVSS 3.1CRITICAL 9.9
- TI-2025-04465 Path Traversal Leading to RCE by Any Authenticated Mattermost User CVSS 3.1CRITICAL 9.9
- TI-2017-14068 An issue was discovered in Mattermost Server before 3.6.2. CVSS 3.1CRITICAL 9.8
- TI-2017-14060 An issue was discovered in Mattermost Server before 3.8.2, 3.7.5, and 3.6.7. CVSS 3.1CRITICAL 9.8
- TI-2017-14048 An issue was discovered in Mattermost Server before 4.1.0, 4.0.4, and 3.10.3. CVSS 3.1CRITICAL 9.8
- TI-2025-14360 Arbitrary file read via block duplication in Mattermost Boards CVSS 3.1CRITICAL 9.9
Sources
- CVE-2026-27769 · CVE Program
- CVE-2026-27769 · NVD
- FIRST EPSS
- GHSA-mxxh-fmjq-j6x4 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-27769 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences