Denial of Service via specially crafted block fields in Mattermost Boards
Priority LOW 34CWE-400Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- 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 · NVD. Fix status from CNA and GitHub. Impact type from CWE-400.
Summary
Mattermost fails to properly limit the characters allowed in different fields of a block in Mattermost Boards allowing a attacker to consume excessive resources, possibly leading to Denial of Service, by patching the field of a block using a specially crafted string.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00723 54th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 9.1.1, 9.0.2, 7.8.13 +1github.com/mattermost/mattermost/server/v8 (Go): 9.1.1, 9.0.2, 8.1.4+1 more product
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 | up to 7.8.12; up to 8.1.3; up to 9.0.1; up to 9.1.0 | 9.1.1, 9.0.2, 7.8.13, 8.1.4 | Patch available | CNA |
| — | github.com/mattermost/mattermost/server/v8 (Go) | 9.1.0 to before 9.1.1 | 9.1.1 | Patch available | GHSA-c37r-v8jx-7cv2 |
| — | github.com/mattermost/mattermost/server/v8 (Go) | 9.0.0 to before 9.0.2 | 9.0.2 | Patch available | GHSA-c37r-v8jx-7cv2 |
| — | github.com/mattermost/mattermost/server/v8 (Go) | before 8.1.4 | 8.1.4 | Patch available | GHSA-c37r-v8jx-7cv2 |
| — | github.com/mattermost/mattermost-server/v6 (Go) | before 7.8.13 | 7.8.13 | Patch available | GHSA-c37r-v8jx-7cv2 |
- Mattermost VendorMattermost Affected up to 7.8.12; up to 8.1.3; up to 9.0.1; up to 9.1.0 Fixed in 9.1.1, 9.0.2, 7.8.13, 8.1.4 Patch available CNA
- github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected 9.1.0 to before 9.1.1 Fixed in 9.1.1 Patch available GHSA-c37r-v8jx-7cv2
- github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected 9.0.0 to before 9.0.2 Fixed in 9.0.2 Patch available GHSA-c37r-v8jx-7cv2
- github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected before 8.1.4 Fixed in 8.1.4 Patch available GHSA-c37r-v8jx-7cv2
- github.com/mattermost/mattermost-server/v6 (Go) Vendor— Affected before 7.8.13 Fixed in 7.8.13 Patch available GHSA-c37r-v8jx-7cv2
CPE configurations NVD · 2
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:mattermost:mattermost:*:*:*:*:*:*:*:* | up to 7.8.12; 8.0.0 – 8.1.3; 9.0.0 – 9.0.1 | Vulnerable | Mattermost |
| cpe:2.3:a:mattermost:mattermost:9.1.0:*:*:*:*:*:*:* | 9.1.0 | Vulnerable | Mattermost |
- cpe:2.3:a:mattermost:mattermost:*:*:*:*:*:*:*:* Versions up to 7.8.12; 8.0.0 – 8.1.3; 9.0.0 – 9.0.1 Vulnerable ·Mattermost
- cpe:2.3:a:mattermost:mattermost:9.1.0:*:*:*:*:*:*:* Versions 9.1.0 Vulnerable ·Mattermost
Remediation
- Fix · CNA Mattermost (Mattermost) Fixed in 9.1.1, 9.0.2, 7.8.13, 8.1.4
- Fix · GHSA-c37r-v8jx-7cv2 github.com/mattermost/mattermost/server/v8 (Go) Fixed in 9.1.1 Advisory →
- Fix · GHSA-c37r-v8jx-7cv2 github.com/mattermost/mattermost/server/v8 (Go) Fixed in 9.0.2 Advisory →
- Fix · GHSA-c37r-v8jx-7cv2 github.com/mattermost/mattermost/server/v8 (Go) Fixed in 8.1.4 Advisory →
- Fix · GHSA-c37r-v8jx-7cv2 github.com/mattermost/mattermost-server/v6 (Go) Fixed in 7.8.13 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2023-40703
- 2026-10-03 Alias added: GHSA-c37r-v8jx-7cv2
References
More Mattermost vulnerabilities
- TI-2024-26695 Malicious remote can invite itself to an arbitrary local channel CVSS 3.1CRITICAL 9.6
- TI-2023-02056 Oauth authorization codes do not expire when deauthorizing an oauth2 app CVSS 3.1CRITICAL 9.1
- TI-2019-15069 An issue was discovered in Mattermost Mobile Apps before 1.26.0. CVSS 3.1CRITICAL 9.1
- TI-2024-26233 Malicious remote can add users to arbitrary teams and channels CVSS 3.1HIGH 8.7
- TI-2024-26746 Permanently local data deletion by malicious remote CVSS 3.1HIGH 8.7
- TI-2023-06508 Injection in Mattermost CVSS 3.1HIGH 8.8
Sources
- CVE-2023-40703 · CVE Program
- CVE-2023-40703 · NVD
- FIRST EPSS
- GHSA-c37r-v8jx-7cv2 · GitHub Advisory Database · CC BY 4.0
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