Medium · CVSS 4.3CVE-2026-86349

Mattermost Server Algorithmic DoS via Unbounded Markdown Block NestingCVE-2026-86349

Answer in brief

CVE-2026-86349 records a Medium severity (CVSS 4.3) vulnerability in Mattermost Server Algorithmic DoS via Unbounded Markdown Block Nesting. The current sources do not mark it as known exploited. The current feed maps Mattermost/Mattermost (generic), Mattermost/Mattermost (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 14, 2026Updated Oct 7, 2026Source checked Oct 29, 2026First seen by HOL Sep 14, 2026Material review Oct 7, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 4.3
Exploitation: Not marked as known exploited
Affected software: 3 mapped packages or products
Fix availability: Not reported

Why this deserves its current priority

CVSS is 4.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Mattermost/Mattermost (generic), Mattermost/Mattermost (generic). Check affected ranges and fixed versions before updating.

Affected products and reported versions
Product	Affected versions	Fixed versions
cpe:2.3:a:mattermost:mattermost_server::::::::	Not reported	Not reported

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Mattermost/Mattermostgeneric	11.9.0 \|\| 11.8.0 \|\| 11.7.0 \|\| 10.11.0	Not reported
Mattermost/Mattermostgeneric	>=11.9.0 <=11.9.0 \|\| >=11.8.0 <=11.8.4 \|\| >=11.7.0 <=11.7.8 \|\| >=10.11.0 <=10.11.22	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Mattermost/Mattermost, Mattermost/Mattermost.
Review the reported fix. Source-reported solution: Update Mattermost to versions 11.10.0, 11.9.1, 11.8.5, 11.7.9, 10.11.23 or higher.

Evidence timeline and material changes

Published upstream
Sep 14, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 7, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 14, 2026

Sources and claim methodology

Source referencemattermost.com

Upstream source 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

Quoted source text, attributed separately from HOL analysis.