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Vulnerability record · CVE-2026-3473 · published 22 May 2026

CVE-2026-3473: Mattermost server insecure direct object reference vulnerability

Mattermost · Mattermost Server

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate file ownership and access control, which allows an authenticated user to access and download files belonging to other users or teams via crafted Boards API requests using valid file IDs.. Mattermost Advisory ID: MMSA-2026-00620

7.1 CVSS 3.1 High EPSS 0.25% · top 85.6% CWE-639 · Insecure direct object reference
7.1CVSS 3.1 base score
0.25%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
1References
23 Jul 2026Last modified by NVD

Description

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate file ownership and access control, which allows an authenticated user to access and download files belonging to other users or teams via crafted Boards API requests using valid file IDs.. Mattermost Advisory ID: MMSA-2026-00620

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://mattermost.com/security-updates Vendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.9CVE-2026-4858Mattermost server path traversal vulnerabilityMattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to check integration URL for path traversal which …EPSS 0.40%9.9CVE-2025-12421Mattermost server vulnerabilityMattermost versions 11.0.x <= 11.0.2, 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12 fail to to verify that the token used during the code…EPSS 0.35%9.9CVE-2025-12419Mattermost server vulnerabilityMattermost versions 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12, 11.0.x <= 11.0.3 fail to properly validate OAuth state tokens during O…EPSS 0.35%9.9CVE-2025-4981Mattermost server uncontrolled search path element vulnerabilityMattermost versions 10.5.x <= 10.5.5, 9.11.x <= 9.11.15, 10.8.x <= 10.8.0, 10.7.x <= 10.7.2, 10.6.x <= 10.6.5 fail to sanitize filenames in the archi…EPSS 0.85%9.8CVE-2023-6458Mattermost server injection vulnerabilityMattermost webapp fails to validate route parameters in/<TEAM_NAME>/channels/<CHANNEL_NAME> allowing an attacker to perform a client-side path traver…EPSS 0.64%9.8CVE-2017-18908Mattermost server improper authentication vulnerabilityAn issue was discovered in Mattermost Server before 4.0.0, 3.10.2, and 3.9.2. A password-reset request was sometime sent to an attacker-provided e-ma…EPSS 1.2%9.8CVE-2017-18915Mattermost server incorrect default permissions vulnerabilityAn issue was discovered in Mattermost Server before 3.8.2, 3.7.5, and 3.6.7. After a restart of a server, an attacker might suddenly gain API Endpoin…EPSS 1.2%9.8CVE-2017-18920Mattermost server vulnerabilityAn issue was discovered in Mattermost Server before 3.6.2. The WebSocket feature does not follow the Same Origin Policy.EPSS 1.2%

Source: NIST National Vulnerability Database (record CVE-2026-3473), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.