Path traversal in Mattermost Agents plugin mention reminder allows plugin replacement via crafted post

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10 fail to validate the target post ID in the Agents plugin's mention reminder component, which allows an authenticated user who can post in a channel visible to a system administrator to cause the administrator's browser to send an unintended API request, resulting in replacement of an installed plugin and code execution on the server, via a crafted post containing a forged mention reminder that the administrator clicks. Mattermost Advisory ID: MMSA-2026-00742

Source published

28 Oct 2026 21:41:15 UTC

Source modified

30 Oct 2026 03:56:14 UTC

Observed here

30 Oct 2026 04:48:55 UTC

Source terms

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CVSS 3.1 · 8.0 CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:H