Is CVE-2026-6342 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-6342 being exploited in the wild.

How severe is CVE-2026-6342?

Medium severity, with a CVSS score of 4.3, published 18 May 2026.

Which products and versions are affected?

Mattermost Plugins <=11.5, 11.1.5, 10.13.11, 11.3.4.0.

Is there a fix for CVE-2026-6342?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-6342 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-6342?

Check whether you run Mattermost Plugins 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-2026-6342: Mattermost Plugins incorrect authorization in group subscriptions

Q: Which products and versions are affected?

Mattermost Plugins <=11.5, 11.1.5, 10.13.11, 11.3.4.0.

Q: Is there a fix for CVE-2026-6342?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

Q: How is CVE-2026-6342 attacked?

It is attacked over the network, in a software library.

Q: Am I affected by CVE-2026-6342?

Check whether you run Mattermost Plugins 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-2026-6342 · Severity: medium · CVSS 4.3 · Published 2026-05-18

Mattermost Plugins, which extend the functionality of the Mattermost collaboration platform, contain a security flaw in how they manage group subscriptions. An authorized user could bypass intended restrictions to join or subscribe to groups that should be off-limits by exploiting a naming inconsistency. This could lead to unauthorized access to group-based communications or notifications that were meant to be restricted to specific whitelisted sets.

Technologies: Mattermost Plugins. Vendors: Mattermost.

Quick answers

Is CVE-2026-6342 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-6342 being exploited in the wild.
How severe is CVE-2026-6342?: Medium severity, with a CVSS score of 4.3, published 18 May 2026.
Which products and versions are affected?: Mattermost Plugins <=11.5, 11.1.5, 10.13.11, 11.3.4.0.
Is there a fix for CVE-2026-6342?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-6342 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-6342?: Check whether you run Mattermost Plugins 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.

Technical details

An incorrect authorization vulnerability (CWE-863) exists in Mattermost Plugins due to insufficient namespace validation. The software fails to strictly enforce whitelisting for group subscriptions, allowing an attacker with low-level privileges to subscribe to unauthorized groups if those groups share a name prefix with a legitimate, whitelisted group. This is a network-reachable vulnerability that requires authentication but no user interaction. The flaw allows for unauthorized integrity changes regarding group subscriptions. Fixes are typically addressed in subsequent Mattermost release cycles.

Affected products

Mattermost Mattermost Plugins <=11.5, 11.1.5, 10.13.11, 11.3.4.0

Timeline

2026-05-18: disclosed: CVE published by NVD and Mattermost

References

https://mattermost.com/security-updates

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