Is CVE-2026-6689 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-6689 being exploited in the wild.

How severe is CVE-2026-6689?

Medium severity, with a CVSS score of 4.3, published 12 June 2026.

Which products and versions are affected?

github.com/mattermost/mattermost-server (Go) SEMVER:introduced=10.11.0+incompatible,fixed=10.11.17+incompatible,introduced=11.5.0+incompatible,fixed=11.5.5+incompatible,introduced=11.6.0+incompatible,fixed=11.6.1+incompatible, SEMVER:introduced=11.6.0,fixed=11.6.1; github.com/mattermost/mattermost-server/v5 (Go) SEMVER:introduced=0; github.com/mattermost/mattermost-server/v6 (Go) SEMVER:introduced=0; github.com/mattermost/mattermost/server/v8 (Go) SEMVER:introduced=8.0.0-20250731163400-5b955468ea1e,fixed=8.0.0-20260501144115-7d6816abdfd1; and 1 more.

Is there a fix for CVE-2026-6689?

Yes. github.com/mattermost/mattermost-server (Go): upgrade to 11.6.1, 11.6.1+incompatible or later; github.com/mattermost/mattermost/server/v8 (Go): upgrade to 8.0.0-20260501144115-7d6816abdfd1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-6689 attacked?

It is attacked over the network, in a hosted service.

Am I affected by CVE-2026-6689?

Check whether you run github.com/mattermost/mattermost-server (Go), github.com/mattermost/mattermost-server/v5 (Go), github.com/mattermost/mattermost-server/v6 (Go) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-6689: Mattermost missing authorization for invite settings during team creation

CVE-2026-6689 · Severity: medium · CVSS 4.3 · Published 2026-06-12

Mattermost failed to enforce permission checks when creating teams with invite-controlled settings (open invite or domain restrictions). An authenticated user with team creation rights but without invite management permissions could bypass access controls by setting these options during team creation, actions they would normally be blocked from performing on existing teams. This allows unauthorized configuration of who can join a team.

Technologies: github.com/mattermost/mattermost-server (Go), github.com/mattermost/mattermost-server/v5 (Go), github.com/mattermost/mattermost-server/v6 (Go), github.com/mattermost/mattermost/server/v8 (Go), Mattermost Server. Vendors: Go, Mattermost.

Quick answers

Is CVE-2026-6689 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-6689 being exploited in the wild.
How severe is CVE-2026-6689?: Medium severity, with a CVSS score of 4.3, published 12 June 2026.
Which products and versions are affected?: github.com/mattermost/mattermost-server (Go) SEMVER:introduced=10.11.0+incompatible,fixed=10.11.17+incompatible,introduced=11.5.0+incompatible,fixed=11.5.5+incompatible,introduced=11.6.0+incompatible,fixed=11.6.1+incompatible, SEMVER:introduced=11.6.0,fixed=11.6.1; github.com/mattermost/mattermost-server/v5 (Go) SEMVER:introduced=0; github.com/mattermost/mattermost-server/v6 (Go) SEMVER:introduced=0; github.com/mattermost/mattermost/server/v8 (Go) SEMVER:introduced=8.0.0-20250731163400-5b955468ea1e,fixed=8.0.0-20260501144115-7d6816abdfd1; and 1 more.
Is there a fix for CVE-2026-6689?: Yes. github.com/mattermost/mattermost-server (Go): upgrade to 11.6.1, 11.6.1+incompatible or later; github.com/mattermost/mattermost/server/v8 (Go): upgrade to 8.0.0-20260501144115-7d6816abdfd1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-6689 attacked?: It is attacked over the network, in a hosted service.
Am I affected by CVE-2026-6689?: Check whether you run github.com/mattermost/mattermost-server (Go), github.com/mattermost/mattermost-server/v5 (Go), github.com/mattermost/mattermost-server/v6 (Go) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

github.com/mattermost/mattermost-server (Go): upgrade to 11.6.1, 11.6.1+incompatible or later
```
go get github.com/mattermost/mattermost-server@v11.6.1+incompatible
```
github.com/mattermost/mattermost/server/v8 (Go): upgrade to 8.0.0-20260501144115-7d6816abdfd1 or later
```
go get github.com/mattermost/mattermost/server/v8@v8.0.0-20260501144115-7d6816abdfd1
```

Technical details

This is a missing authorization vulnerability (CWE-862) in Mattermost's team creation endpoint. The root cause is an inconsistent permission check: the PermissionInviteUser authorization was only enforced on team update/patch operations but not during initial team creation via POST /api/v4/teams. An authenticated attacker holding PermissionCreateTeam can supply allow_open_invite: true or a non-empty allowed_domains parameter to make the newly created team publicly joinable or restrict membership by domain, despite lacking PermissionInviteUser. The vulnerability requires network access to the Mattermost API and valid authentication credentials (PR:L), with no user interaction needed. The fix aligns permission checks between team creation and team update operations, enforced in patched versions 10.11.17, 11.5.5, 11.6.2, and 11.7.0.

Affected products

Mattermost Mattermost Server 10.11.0–10.11.15, 11.5.0–11.5.4, 11.6.0–11.6.1

Identifiers

CVE-2026-6689
GHSA-c28q-m4gf-vg4q
GO-2026-6283

Timeline

2026-06-12: disclosed: Vulnerability published in GitHub Advisory Database and NVD
2026-05-04: patched: Fixes merged into release branches; patched versions released (10.11.17, 11.5.5, 11.6.2, 11.7.0)

References

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