CVE-2026-6850 json
Crafted message attachment causes client-side denial of service via markdown parser regex backtracking in Mattermost
published 2026-07-13 3 mo ago modified 2026-07-13 3 mo ago also EUVD-2026-43313
- cvss
- 6.5
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.4%
- EPSS 0.4% chance of exploitation in 30 days, percentile 36%
- public exploits
- 0
- none known
Summary
Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate the length and content of message attachment field values, which allows an authenticated attacker to cause a denial of service for all users in a channel via a post containing a specially crafted payload that triggers catastrophic backtracking in the client-side markdown parser.. Mattermost Advisory ID: MMSA-2026-00658
Patch / fix
- Mattermost Mattermost 10.11.20, 11.6.5, 11.7.3, 11.8.0
CISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 3 mo ago
Exploit prediction
0.42% chance of exploitation in the next 30 days, higher than 36% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 6.5 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
Affected products
- Mattermost Mattermost
Classification
- Weakness
-
- CWE-1333 Inefficient Regular Expression Complexity
References
-
mattermost.com
/security-updates
vendor-advisory
Sources
- CVE List CVE-2026-6850
- NVD CVE-2026-6850
Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.