CVE-2026-18795
Missing server side validation allowed user to quarantine a DM and GM post
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to enforce DM/GM check on server side which allows an authenticated user to quarantine a post belonging to DM or GM via direct API call.. Mattermost Advisory ID: MMSA-2026-00756
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- Low
- User interaction
- None
What an attacker can affect
- Confidentiality
- High
- Integrity
- Low
- Availability
- Low
Exploit likelihood
What each source reports
CVE List Score used
Missing server side validation allowed user to quarantine a DM and GM post
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to enforce DM/GM check on server side which allows an authenticated user to quarantine a post belonging to DM or GM via direct API call.. Mattermost Advisory ID: MMSA-2026-00756
- Record
CVE-2026-18795- CVSS 3.1
- 6.4 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L - Weakness
- CWE-862
- Updated
- 2026-11-02
EUVDEUVD-2026-102813
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to enforce DM/GM check on server side which allows an authenticated user to quarantine a post belonging to DM or GM via direct API call.. Mattermost Advisory ID: MMSA-2026-00756
- Record
EUVD-2026-102813- CVSS 3.1
- 6.4 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-c5qm-9j4f-82mg
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail...
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to enforce DM/GM check on server side which allows an authenticated user to quarantine a post belonging to DM or GM via direct API call.. Mattermost Advisory ID: MMSA-2026-00756
- Record
GHSA-c5qm-9j4f-82mg- CVSS 3.1
- 6.4 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L - Weakness
- CWE-862
- Updated
- 2026-11-02
NVD
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to enforce DM/GM check on server side which allows an authenticated user to quarantine a post belonging to DM or GM via direct API call.. Mattermost Advisory ID: MMSA-2026-00756
- Record
CVE-2026-18795- CVSS 3.1
- 6.4 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L - Weakness
- CWE-862
- Updated
- 2026-11-02
OSV
Missing server side validation allowed user to quarantine a DM and GM post
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to enforce DM/GM check on server side which allows an authenticated user to quarantine a post belonging to DM or GM via direct API call.. Mattermost Advisory ID: MMSA-2026-00756
- Record
CVE-2026-18795- CVSS 3.1
- 6.4 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L - Weakness
- CWE-862
- Updated
- 2026-11-02
Affected products
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-18795 is a medium vulnerability (CVSS 6.4) in Mattermost, published October 16, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.15%, the 4th percentile. No source names a fixed version.