CVE-2026-9708
Received Received - Intake

Incoming Webhook User Access Bypass in Mattermost

Publication date: 2026-07-13

Last updated on: 2026-07-13

Assigner: Mattermost, Inc.

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

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Meta Information

Published
2026-07-13
Last Modified
2026-07-13
Generated
2026-07-13
AI Q&A
2026-07-13
EPSS Evaluated
N/A
NVD
CVE-2026-9708
EUVD
EUVD-2026-43308

Affected Vendors & Products

Showing 3 associated CPEs
Vendor Product Version / Range
mattermost mattermost to 11.7.2 (inc)
mattermost mattermost to 11.6.4 (inc)
mattermost mattermost to 10.11.19 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-639 The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.

Attack-Flow Graph

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Executive Summary

This vulnerability affects certain versions of Mattermost (11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19) where the system fails to verify that an incoming webhook user has permission to access the target team or channel.

As a result, a requester who has webhook management permissions can create posts or direct messages that appear to be sent by another user by crafting specific incoming webhook configurations and payloads.

Impact Analysis

This vulnerability can lead to impersonation within the Mattermost platform, allowing an attacker with webhook management permissions to post messages or direct messages as if they were another user.

Such unauthorized actions can cause misinformation, confusion, or misuse of trust within teams or channels.

The CVSS score indicates a moderate impact with a base score of 4.9, primarily affecting integrity without impacting confidentiality or availability.

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