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Mattermost Desktop App CVE-2026-8075

| EUVDEUVD-2026-45157 MEDIUM
Improper Check for Unusual or Exceptional Conditions (CWE-754)
2026-07-17 Mattermost GHSA-rm64-886x-w6qc
Denial Of Service Mattermost
6.5
CVSS 3.1 · Vendor: Mattermost
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Severity by source

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

Network-delivered via posted link (AV:N), trivial complexity (AC:L), requires only a valid account to post (PR:L), auto-triggered on render (UI:N), client crash only with no data exposure (C:N/I:N/A:H).

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

Primary rating from Vendor (Mattermost).

CVSS VectorVendor: Mattermost

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

1
Analysis Generated
Jul 17, 2026 - 10:45 vuln.today

DescriptionCVE.org

Mattermost Desktop App versions <=6.2 5.5.13 6.0.2.0 fail to properly null check when checking for headers in the Mattermost Desktop App which allows any user to crash another channel members Desktop App via posting a malicious link with an embedded image that misses one of those headers. Mattermost Advisory ID: MMSA-2026-00668

AnalysisAI

Improper null checking in Mattermost Desktop App versions ≤6.2, 5.5.13, and 6.0.2.0 enables any authenticated channel member to crash the Desktop App of all other members in the same channel by posting a crafted link containing an embedded image served without expected HTTP headers. The crash is client-side and can be made persistent if the malicious message remains in the channel, forcing repeated crashes each time an affected client reconnects. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Obtain low-privilege Mattermost account
Delivery
Host image on header-stripping server
Exploit
Post crafted link in shared channel
Execution
Target Desktop App auto-renders link preview
Persist
Null dereference on missing header
Impact
Desktop App crashes
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Vulnerability AssessmentAI

Exploitation The attacker must hold a valid Mattermost account with at least standard message-posting permissions in a channel shared with the target users - low-privilege authenticated access (PR:L per CVSS). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 3.1 vector (AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) scores 6.5 Medium. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An authenticated Mattermost user with posting rights in a shared channel hosts an image on an attacker-controlled server configured to omit one or more HTTP headers expected by the Desktop App's preview renderer. The attacker posts a link containing this image to the channel; when other members' Desktop Apps automatically attempt to render the link preview, the null check failure triggers an immediate application crash. …
Remediation Upgrade the Mattermost Desktop App to a version beyond the affected ceiling per the vendor security advisory at https://mattermost.com/security-updates. … Detailed patch versions, workarounds, and compensating controls in full report.
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CVE-2026-8075 vulnerability details – vuln.today
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