GHSA-9p44-r552-4wp9 CVE-2026-7184 GO-2026-6282

Mattermost doesn't sanitize the Remote Cluster API response on PATCH operations

Medium Go

Severity: 6.5 / 10; Medium · CVSS 3.1
Exploit chance (EPSS): 0.26%; Chance of exploitation in the next 30 days. Higher than 17.17% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-201 Insertion of Sensitive Information Into Sent Data
Fix: Available; 2 packages have a fixed version

Description

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15 fail to sanitize the Remote Cluster API response on PATCH operations, which allows authenticated users with the {{manage_secure_connections}} permission to obtain remote cluster authentication tokens via a PATCH request to the remote cluster endpoint. Mattermost Advisory ID: MMSA-2026-00662

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, < 11.5.5`	`11.5.5`
github.com/mattermost/mattermost-server	`>= 10.11.0, < 10.11.16`	`10.11.16`
github.com/mattermost/mattermost-server	`>= 10.11.0+incompatible, < 10.11.16+incompatible` `>= 11.5.0+incompatible, < 11.5.5+incompatible` `>= 11.6.0+incompatible, < 11.6.1+incompatible`	`10.11.16+incompatible` `11.5.5+incompatible` `11.6.1+incompatible`
github.com/mattermost/mattermost-server/v5	`all versions`	No fix yet
github.com/mattermost/mattermost-server/v6	`all versions`	No fix yet
github.com/mattermost/mattermost/server/v8	`>= 8.0.0-20250731163400-5b955468ea1e, < 8.0.0-20260428142921-bd8fc9222672`	`8.0.0-20260428142921-bd8fc9222672`

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

github.com/mattermost/mattermost/server/v8 Go → `8.0.0-20260428142921-bd8fc9222672`

go

go get github.com/mattermost/mattermost/server/v8@v8.0.0-20260428142921-bd8fc9222672 && go mod tidy

Severity breakdown

CVSS 3.1 6.5

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

Attack vector: Network
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

Weakness

CWE-201: Insertion of Sensitive Information Into Sent Data

The code transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor.

How to prevent it

Requirements: Specify which data in the software should be regarded as sensitive. Consider which types of users should have access to which types of data.
Implementation: Ensure that any possibly sensitive data specified in the requirements is verified with designers to ensure that it is either a calculated risk or mitigated elsewhere. Any information that is not necessary to the functionality should be removed in order to lower both the overhead and the possibility of security sensitive data being sent.
System Configuration: Setup default error messages so that unexpected errors do not disclose sensitive information.
Architecture and Design: Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

References

Advisories

Packages

github.com/mattermost/mattermost

Timeline

Jun 12, 2026 Published
Aug 26, 2026 Last updated by the source
Nov 1, 2026 Latest EPSS score

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-8qq9-cqj8-82w4 Mattermost doesn't sanitize FileInfo.Name received from federated peers during shared channel file sync	High	Also affects github.com/mattermost/mattermost-server

Is this in your code?

MergeHarbor checks every repository's dependencies against this database, ranks what matters by exploitability and reachability, routes it to the owning team and opens the fix pull request.

Check your repos with MergeHarbor