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Mattermost CVE-2026-86348

| EUVDEUVD-2026-77481 MEDIUM
Incorrect Type Conversion or Cast (CWE-704)
2026-09-14 Mattermost GHSA-hw33-g6h4-vc78
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

Requires authenticated session (PR:L) to reach plugin handler; impact strictly limited to plugin availability (A:L) with no confidentiality or integrity compromise and no scope change.

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

2
Analysis Generated
Sep 15, 2026 - 08:28 vuln.today
CVE Published
Sep 14, 2026 - 13:52 cve.org
MEDIUM 4.3

DescriptionCVE.org

Mattermost versions <=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0 fail to recover from handler panics, which allows an authenticated user to crash the plugin via a post-action request with an unexpected field type.. Mattermost Advisory ID: MMSA-2026-00701

AnalysisAI

Plugin handler panic recovery failure in Mattermost allows authenticated users to crash installed plugins by sending a post-action request containing a field with an unexpected type. Affected versions span multiple maintained release branches (≤11.9, 11.0.9, 11.4.8, 11.7.7, 10.22.11.0) as disclosed under MMSA-2026-00701. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation Exploitation requires a valid Mattermost user account at minimum privilege level (PR:L - standard authenticated session, no administrative rights needed). … 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) is well-calibrated: the attack requires a valid authenticated session but no elevated privileges, and consequence is strictly limited to low availability impact against a single plugin rather than the core server. … 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 patched releases identified in Mattermost Security Advisory MMSA-2026-00701 - consult https://mattermost.com/security-updates for the exact fixed build numbers corresponding to the 11.9, 11.0.9, 11.4.8, 11.7.7, and 10.22.11.0 branches, as specific patch versions were not independently confirmed from the available reference data. … Detailed patch versions, workarounds, and compensating controls in full report.
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CVE-2026-86348 vulnerability details – vuln.today
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