GHSA-7pf2-9c95-w332 CVE-2026-3473 GO-2026-5817
Mattermost doesn't validate file ownership and access control
- Severity
- 7.1 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 0.15%
- Chance of exploitation in the next 30 days. Higher than 4.09% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-639 Authorization Bypass Through User-Controlled Key
- Fix
11.6.1- Upgrade github.com/mattermost/mattermost-server to this version or later
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.
Affected versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| github.com/mattermost/mattermost-server | >= 11.6.0, < 11.6.1 |
11.6.1 |
| github.com/mattermost/mattermost-server | >= 11.5.0, < 11.5.4 |
11.5.4 |
| github.com/mattermost/mattermost-server | >= 11.4.0, < 11.4.5 |
11.4.5 |
| github.com/mattermost/mattermost-server | >= 10.11.0, < 10.11.15 |
10.11.15 |
| github.com/mattermost/mattermost-server | >= 10.11.0+incompatible, < 10.11.15+incompatible>= 11.4.0+incompatible, < 11.4.5+incompatible>= 11.5.0+incompatible, < 11.5.4+incompatible>= 11.6.0+incompatible, < 11.6.1+incompatible |
10.11.15+incompatible11.4.5+incompatible11.5.4+incompatible11.6.1+incompatible |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
github.com/mattermost/mattermost-server Go → 11.6.1
- go
go get github.com/mattermost/mattermost-server@v11.6.1 && go mod tidy
Severity breakdown
CVSS 3.1 7.1
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- Low
- Availability
- None
Weakness
CWE-639: Authorization Bypass Through User-Controlled Key
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.
How to prevent it
- Architecture and Design: For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested.
- Architecture and Design, Implementation: Make sure that the key that is used in the lookup of a specific user's record is not controllable externally by the user or that any tampering can be detected.
- Architecture and Design: Use encryption in order to make it more difficult to guess other legitimate values of the key or associate a digital signature with the key so that the server can verify that there has been no tampering.
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-xmfh-3ccg-c9fx Mattermost has an Incorrect Authorization issue | Low | Also affects github.com/mattermost/mattermost-server |
| GHSA-h998-hxxj-8q83 Mattermost doesn't invalidate cached authentication state for active WebSocket connections during global session revocation | Medium | Also affects github.com/mattermost/mattermost-server |
| GHSA-g5vr-6pgg-74qv Mattermost doesn't enforce bot-specific permission checks on the user active status endpoint | Low | Also affects github.com/mattermost/mattermost-server |
| GHSA-jqgv-39mg-7c2r Mattermost doesn't authenticate Atlassian Connect installed callbacks, allowing a remote unauthenticated attacker to inject a rogue sharedSecret | Medium | Also affects github.com/mattermost/mattermost-server |
| GHSA-mxq2-5jpg-7474 Mattermost doesn't validate channel ownership of an existing subscription before applying edits | Medium | Also affects github.com/mattermost/mattermost-server |
| GHSA-2g8v-grq3-hq2g Mattermost doesn't enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler | Medium | Also affects github.com/mattermost/mattermost-server |
| GHSA-6hxm-w4hv-vgvw Mattermost doesn't require role-management authorization when setting the scheme_admin flag on group syncable link and patch endpoints | High | Also affects github.com/mattermost/mattermost-server |
| GHSA-9p44-r552-4wp9 Mattermost doesn't sanitize the Remote Cluster API response on PATCH operations | Medium | Also affects github.com/mattermost/mattermost-server |
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