Authenticated plugin crash via unchecked post-action types
Published Sep 14, 2026 · Updated Sep 14, 2026
Improper input validation in Mattermost MS Calendar allows remote authenticated users to crash the plugin via a malformed post-action request. The postActionConfirmStatusChange handler performs unchecked string assertions on change_to and pretty_change_to values, so an unexpected field type triggers a panic that the HTTP entrypoint does not recover. A valid Mattermost account and an enabled integration are required; the resulting panic terminates the plugin process rather than the Mattermost server.
Summary
What happened
Improper input validation in Mattermost MS Calendar allows remote authenticated users to crash the plugin via a malformed post-action request. The postActionConfirmStatusChange handler performs unchecked string assertions on change_to and pretty_change_to values, so an unexpected field type triggers a panic that the HTTP entrypoint does not recover. A valid Mattermost account and an enabled integration are required; the resulting panic terminates the plugin process rather than the Mattermost server.
The record
- CVE
- CVE-2026-86348
- Published
- Sep 14, 2026
- Updated
- Sep 14, 2026
- Vendor
- Mattermost
- Product
- Mattermost
- Classifications
- T1499
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Sep 14, 2026CVE publishedPublication date reported by the CVE source.
- Sep 14, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=<=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0 <=<=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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