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Mattermost EUVDEUVD-2026-77480

| CVE-2026-86349 MEDIUM
Inefficient Algorithmic Complexity (CWE-407)
2026-09-14 Mattermost GHSA-6mc8-c94m-mjg8
Denial Of Service Mattermost
4.3
CVSS 3.1 · Vendor: Mattermost
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Severity by source

Vendor (Mattermost) PRIMARY
4.3 MEDIUM
AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
vuln.today AI
4.3 MEDIUM

Authenticated network user required (PR:L, AV:N); parser flaw needs no special conditions (AC:L); impact is availability-only, partial (A:L), with no confidentiality or integrity consequence.

3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Primary rating from Vendor (Mattermost).

CVSS VectorVendor: Mattermost

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

Lifecycle Timeline

1
Analysis Generated
Sep 15, 2026 - 08:27 vuln.today

DescriptionCVE.org

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

AnalysisAI

Mattermost's server-side Markdown parser across versions 10.11.x through 11.9.0 fails to enforce a nesting depth limit, allowing any authenticated user to cause CPU resource exhaustion by posting a message containing pathologically deep blockquote or list item nesting. The vulnerability is classified CWE-407 (Inefficient Algorithmic Complexity), producing a denial-of-service condition that degrades availability for all users of the affected instance. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation Requires a valid, authenticated Mattermost user account with posting rights in at least one channel (CVSS PR:L confirmed by vendor). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The vendor-assigned CVSS 4.3 (AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L) accurately reflects a constrained-impact scenario: network-reachable, low complexity, but requiring authenticated access (PR:L), with only partial availability impact and no confidentiality or integrity exposure. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Upgrade to the next patched release in each affected branch as specified by Mattermost advisory MMSA-2026-00707, available at https://mattermost.com/security-updates. … Detailed patch versions, workarounds, and compensating controls in full report.
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EUVD-2026-77480 vulnerability details – vuln.today
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