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Mattermost EUVDEUVD-2026-77363

| CVE-2026-12882 MEDIUM
Inefficient Algorithmic Complexity (CWE-407)
2026-09-14 Mattermost GHSA-mfv9-qx66-gxm4
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

Network-reachable via standard post API, PR:L because a valid authenticated account is required, A:L for partial availability degradation without crash or data impact.

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

3
Metadata Corrected
Sep 14, 2026 - 11:40 vuln.today
tag: Denial Of Service added
Metadata Corrected
Sep 14, 2026 - 11:40 vuln.today
tag: Information Disclosure removed
Analysis Generated
Sep 14, 2026 - 11:26 vuln.today

DescriptionCVE.org

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to parse Markdown autolinks with unmatched trailing closing parentheses in linear time, which allows an authenticated user with permission to create posts to cause excessive server CPU consumption and degrade availability for other users via specially crafted post or message attachment content. Mattermost Advisory ID: MMSA-2026-00703

AnalysisAI

Mattermost's server-side Markdown autolink parser processes autolinks with unmatched trailing closing parentheses in superlinear time, enabling any authenticated user with post-creation rights to cause excessive CPU consumption and degrade availability for all users on the instance. Affected release trains are 11.9.x through 11.9.0, 11.8.x through 11.8.4, 11.7.x through 11.7.7, and 10.11.x through 10.11.22 across both cloud and self-hosted deployments. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation Exploitation requires a valid, authenticated Mattermost user account with the 'Create Posts' permission granted (PR:L per CVSS). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The NVD-assigned CVSS 4.3 (AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L) accurately reflects the limited impact envelope of this flaw: network-reachable, low authentication barrier, but constrained to partial availability degradation with no confidentiality or integrity implications. … 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 The primary remediation is to upgrade Mattermost to a patched release beyond the affected version ceiling in the applicable branch (11.9.x, 11.8.x, 11.7.x, or 10.11.x). … Detailed patch versions, workarounds, and compensating controls in full report.
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EUVD-2026-77363 vulnerability details – vuln.today
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