Mattermost Server Algorithmic DoS via Unbounded Markdown Block Nesting
Summary
| CVE | CVE-2026-86349 |
|---|---|
| State | PUBLISHED |
| Assigner | Mattermost |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-09-14 14:17:15 UTC |
| Updated | 2026-09-14 14:17:15 UTC |
| Description | Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.8, 10.11.x <= 10.11.22 fail to limit the nesting depth in the server-side Markdown parser which allows an authenticated attacker to cause a denial of service (CPU resource exhaustion) via a crafted post containing deeply nested blockquotes or list items.. Mattermost Advisory ID: MMSA-2026-00707 |
Risk And Classification
Primary CVSS: v3.1 4.3 MEDIUM from [email protected]
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Problem Types: CWE-407 | CWE-407 CWE-407: Inefficient Algorithmic Complexity
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Secondary | 4.3 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L |
| 3.1 | CNA | CVSS | 4.3 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
LowUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
NoneAvailability
LowCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Mattermost | Mattermost | affected 11.9.0 11.9.0 semver | Not specified |
| CNA | Mattermost | Mattermost | affected 11.8.0 11.8.4 semver | Not specified |
| CNA | Mattermost | Mattermost | affected 11.7.0 11.7.8 semver | Not specified |
| CNA | Mattermost | Mattermost | affected 10.11.0 10.11.22 semver | Not specified |
| CNA | Mattermost | Mattermost | unaffected 11.10.0 | Not specified |
| CNA | Mattermost | Mattermost | unaffected 11.9.1 | Not specified |
| CNA | Mattermost | Mattermost | unaffected 11.8.5 | Not specified |
| CNA | Mattermost | Mattermost | unaffected 11.7.9 | Not specified |
| CNA | Mattermost | Mattermost | unaffected 10.11.23 | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| mattermost.com/security-updates | [email protected] | mattermost.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: tr66net (en)
Additional Advisory Data
Solutions
CNA: Update Mattermost to versions 11.10.0, 11.9.1, 11.8.5, 11.7.9, 10.11.23 or higher.
There are currently no legacy QID mappings associated with this CVE.