CVE-2026-9708

Medium

Description

Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate that an assigned incoming webhook user has access to the target team or channel, which allows a requester with webhook management permissions to create posts or direct messages attributed to another user via crafted incoming webhook configuration and payloads.. Mattermost Advisory ID: MMSA-2026-00683

SeverityMedium

CVSS4.9

Exploit probability—

Product

Mattermost Server

PublishedJul 13, 2026

First seenJul 13, 2026

Weakness typeCWE-639Authorization bypass through user-controlled key

How to fix

Update

mattermost mattermost_server10.11.20, 11.6.5, 11.7.3 or later

Vendor advisories

mattermost.com/security-updates

Affected products

Product	Affected versions	Fixed in
mattermost mattermost_server	10.11.0 ≤ v < 10.11.20, 11.6.0 ≤ v < 11.6.5, 11.7.0 ≤ v < 11.7.3	10.11.20, 11.6.5, 11.7.3

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