CVE-2026-18560
Received Received - Intake

Permission Bypass in Mattermost Reveals Flagged Post Status

Publication date: 2026-10-16

Last updated on: 2026-10-16

Assigner: Mattermost, Inc.

Description
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to validate user’s permissions before other validations which allows non-content reviewers to infer a post’s flagged status via direct API call.. Mattermost Advisory ID: MMSA-2026-00754

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Meta Information

Published
2026-10-16
Last Modified
2026-10-16
Generated
2026-10-16
AI Q&A
2026-10-16
EPSS Evaluated
N/A
NVD
CVE-2026-18560
EUVD
EUVD-2026-102746

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
Mattermost Mattermost 11.10.0
Mattermost Mattermost 11.7.0
Mattermost Mattermost 11.9.0
Mattermost Mattermost 11.8.0

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-203 The product behaves differently or sends different responses under different circumstances in a way that is observable to an unauthorized actor.

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Executive Summary

This vulnerability affects Mattermost versions between 11.7.x and 11.10.x. It allows non-content reviewers to check if a post has been flagged by making direct API calls without proper permission validation. The issue arises because permission checks are not performed before other validations.

Impact Analysis

An attacker with reviewer access but not content reviewer privileges could infer whether posts were flagged. This could lead to unauthorized disclosure of moderation actions or sensitive content status.

Mitigation Strategies

Upgrade Mattermost to a version that is not affected by this vulnerability. Specifically, upgrade to versions 11.10.1 or later, 11.7.10 or later, 11.9.2 or later, or 11.8.6 or later as per the Mattermost Advisory ID MMSA-2026-00754.

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