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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
Basic information
Type
unreviewed
Severity
high Advisory on GitHub
Open advisory ↗ Repository advisory
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Source code
Not specified Published (advisory)
2026-05-26 13:30:15 UTC
Updated
2026-05-26 13:30:19 UTC
NVD published
2026-05-22
EPSS Score
Score
Percentile
0.03%
10.22%
CVSS Scores
Base score
Version
Severity
Vector
7.1
3.1
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CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N
Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
CWEs
CWE id
Name
CWE-639
Authorization Bypass Through User-Controlled Key
cvelogic
Threat Intelligence