Time-of-check time-of-use vulnerability in common teams API
Priority LOW 15CWE-367Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- High
- Impact type
- —
- Confidentiality · integrity · availability
- Low · None · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub.
Summary
Mattermost versions 10.11.x <= 10.11.9 fail to properly validate channel membership at the time of data retrieval which allows a deactivated user to learn team names they should not have access to via a race condition in the /common_teams API endpoint.. Mattermost Advisory ID: MMSA-2025-00549
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.0022 12th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 11.3.0, 10.11.10github.com/mattermost/mattermost-server (Go): 10.11.10
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 – 10.11.9 | 11.3.0, 10.11.10 | Patch available | CNA |
| — | github.com/mattermost/mattermost-server (Go) | 10.11.0 to before 10.11.10 | 10.11.10 | Patch available | GHSA-2xf7-hmf6-p64j |
- Mattermost VendorMattermost Affected 10.11.0 – 10.11.9 Fixed in 11.3.0, 10.11.10 Patch available CNA
- github.com/mattermost/mattermost-server (Go) Vendor— Affected 10.11.0 to before 10.11.10 Fixed in 10.11.10 Patch available GHSA-2xf7-hmf6-p64j
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* | 10.11.0 to before 10.11.10 | Vulnerable | Mattermost |
- cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* Versions 10.11.0 to before 10.11.10 Vulnerable ·Mattermost
Remediation
- Fix · CNA Mattermost (Mattermost) Fixed in 11.3.0, 10.11.10
- Fix · GHSA-2xf7-hmf6-p64j github.com/mattermost/mattermost-server (Go) Fixed in 10.11.10 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2026-20796
- 2026-10-03 Alias added: GHSA-2xf7-hmf6-p64j
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-2026-20796 · CVE Program
- CVE-2026-20796 · NVD
- FIRST EPSS
- GHSA-2xf7-hmf6-p64j · GitHub Advisory Database · CC BY 4.0
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