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GHSA-8r89-8w26-cq32Published

Mattermost doesn't verify channel membership when processing AI-assisted message rewrites

Exact source revision recorded 24 Oct 2026 13:19:41 UTC. It does not establish the source's current position. Latest evidence.

Recorded JSON

osv · GHSA-8r89-8w26-cq32

Published

Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint.. Mattermost Advisory ID: MMSA-2026-00645

Source published
18 May 2026 09:31:48 UTC
Source modified
25 Jun 2026 19:56:31 UTC
Observed here
24 Oct 2026 13:19:41 UTC
Source terms
GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Publisher rating · MODERATE

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Sources read 10 Nov 00:29 UTC · 275 of 275 readable · 273 fully read · documentation 469/469 current

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