WebApp crash via improper validation of proto style in attachments
Priority LOW 30CWE-704Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-704 and the CVSS impact.
Summary
Mattermost versions 10.2.x <= 10.2.0, 9.11.x <= 9.11.5, 10.0.x <= 10.0.3, 10.1.x <= 10.1.3 fail to properly validate the style of proto supplied to an action's style in post.props.attachments, which allows an attacker to crash the frontend via crafted malicious input.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00584 48th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 10.3.0, 10.2.1, 9.11.6 +2github.com/mattermost/mattermost/server/v8 (Go): 10.2.1, 10.1.4, 10.0.4 +2
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 | 10.2.0; 9.11.0 – 9.11.5; 10.0.0 – 10.0.3; 10.1.0 – 10.1.3 | 10.3.0, 10.2.1, 9.11.6, 10.0.4, 10.1.4 | Patch available | CNA |
| — | github.com/mattermost/mattermost/server/v8 (Go) | 10.2.0 to before 10.2.1 | 10.2.1 | Patch available | GHSA-8j3q-gc9x-7972 |
| — | github.com/mattermost/mattermost/server/v8 (Go) | 10.1.0 to before 10.1.4 | 10.1.4 | Patch available | GHSA-8j3q-gc9x-7972 |
| — | github.com/mattermost/mattermost/server/v8 (Go) | 10.0.0 to before 10.0.4 | 10.0.4 | Patch available | GHSA-8j3q-gc9x-7972 |
| — | github.com/mattermost/mattermost/server/v8 (Go) | 9.11.0 to before 9.11.6 | 9.11.6 | Patch available | GHSA-8j3q-gc9x-7972 |
| — | github.com/mattermost/mattermost/server/v8 (Go) | before 8.0.0-20241127161322-25ff7a3779a5 | 8.0.0-20241127161322-25ff7a3779a5 | Patch available | GHSA-8j3q-gc9x-7972 |
- Mattermost VendorMattermost Affected 10.2.0; 9.11.0 – 9.11.5; 10.0.0 – 10.0.3; 10.1.0 – 10.1.3 Fixed in 10.3.0, 10.2.1, 9.11.6, 10.0.4, 10.1.4 Patch available CNA
- github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected 10.2.0 to before 10.2.1 Fixed in 10.2.1 Patch available GHSA-8j3q-gc9x-7972
- github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected 10.1.0 to before 10.1.4 Fixed in 10.1.4 Patch available GHSA-8j3q-gc9x-7972
- github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected 10.0.0 to before 10.0.4 Fixed in 10.0.4 Patch available GHSA-8j3q-gc9x-7972
- github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected 9.11.0 to before 9.11.6 Fixed in 9.11.6 Patch available GHSA-8j3q-gc9x-7972
- github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected before 8.0.0-20241127161322-25ff7a3779a5 Fixed in 8.0.0-20241127161322-25ff7a3779a5 Patch available GHSA-8j3q-gc9x-7972
CPE configurations NVD · 2
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* | 9.11.0 to before 9.11.6; 10.0.0 to before 10.0.4; 10.1.0 to before 10.1.4 | Vulnerable | Mattermost |
| cpe:2.3:a:mattermost:mattermost_server:10.2.0:-:*:*:*:*:*:* | 10.2.0 | Vulnerable | Mattermost |
- cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* Versions 9.11.0 to before 9.11.6; 10.0.0 to before 10.0.4; 10.1.0 to before 10.1.4 Vulnerable ·Mattermost
- cpe:2.3:a:mattermost:mattermost_server:10.2.0:-:*:*:*:*:*:* Versions 10.2.0 Vulnerable ·Mattermost
Remediation
- Fix · CNA Mattermost (Mattermost) Fixed in 10.3.0, 10.2.1, 9.11.6, 10.0.4, 10.1.4
- Fix · GHSA-8j3q-gc9x-7972 github.com/mattermost/mattermost/server/v8 (Go) Fixed in 10.2.1 Advisory →
- Fix · GHSA-8j3q-gc9x-7972 github.com/mattermost/mattermost/server/v8 (Go) Fixed in 10.1.4 Advisory →
- Fix · GHSA-8j3q-gc9x-7972 github.com/mattermost/mattermost/server/v8 (Go) Fixed in 10.0.4 Advisory →
- Fix · GHSA-8j3q-gc9x-7972 github.com/mattermost/mattermost/server/v8 (Go) Fixed in 9.11.6 Advisory →
- Fix · GHSA-8j3q-gc9x-7972 github.com/mattermost/mattermost/server/v8 (Go) Fixed in 8.0.0-20241127161322-25ff7a3779a5 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2025-21088
- 2026-10-03 Alias added: GHSA-8j3q-gc9x-7972
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-2025-21088 · CVE Program
- CVE-2025-21088 · NVD
- FIRST EPSS
- GHSA-8j3q-gc9x-7972 · GitHub Advisory Database · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences