Is CVE-2026-6346 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-6346 being exploited in the wild.

How severe is CVE-2026-6346?

High severity, with a CVSS score of 8.7, published 18 May 2026.

Which products and versions are affected?

github.com/mattermost/mattermost-server (Go) SEMVER:introduced=0,fixed=5.3.2-0.20260326202606-fac92f4a71f3, SEMVER:introduced=10.11.0+incompatible,fixed=10.11.14+incompatible,introduced=11.4.0+incompatible,fixed=11.4.4+incompatible,introduced=11.5.0+incompatible,fixed=11.5.2+incompatible; 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=0,fixed=8.0.0-20260326202606-fac92f4a71f3, SEMVER:introduced=11.5.0,fixed=11.5.2; and 1 more.

Is there a fix for CVE-2026-6346?

Yes. github.com/mattermost/mattermost-server (Go): upgrade to 11.5.2+incompatible, 5.3.2-0.20260326202606-fac92f4a71f3 or later; github.com/mattermost/mattermost/server/v8 (Go): upgrade to 11.5.2, 8.0.0-20260326202606-fac92f4a71f3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-6346 attacked?

It is attacked over the network, in a network appliance.

Am I affected by CVE-2026-6346?

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-2026-6346: Mattermost sensitive information disclosure in support packet generation

CVE-2026-6346 · Severity: high · CVSS 8.7 · Published 2026-05-18

Mattermost, a popular collaboration and messaging platform, contains a vulnerability where sensitive configuration data is not properly hidden when generating support diagnostic files. This could allow a system administrator or anyone with access to these support files to view sensitive credentials, such as passwords or API keys, in plain text. Exposure of these credentials could lead to unauthorized access to other integrated corporate systems or the underlying database.

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-2026-6346 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-6346 being exploited in the wild.
How severe is CVE-2026-6346?: High severity, with a CVSS score of 8.7, published 18 May 2026.
Which products and versions are affected?: github.com/mattermost/mattermost-server (Go) SEMVER:introduced=0,fixed=5.3.2-0.20260326202606-fac92f4a71f3, SEMVER:introduced=10.11.0+incompatible,fixed=10.11.14+incompatible,introduced=11.4.0+incompatible,fixed=11.4.4+incompatible,introduced=11.5.0+incompatible,fixed=11.5.2+incompatible; 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=0,fixed=8.0.0-20260326202606-fac92f4a71f3, SEMVER:introduced=11.5.0,fixed=11.5.2; and 1 more.
Is there a fix for CVE-2026-6346?: Yes. github.com/mattermost/mattermost-server (Go): upgrade to 11.5.2+incompatible, 5.3.2-0.20260326202606-fac92f4a71f3 or later; github.com/mattermost/mattermost/server/v8 (Go): upgrade to 11.5.2, 8.0.0-20260326202606-fac92f4a71f3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-6346 attacked?: It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-6346?: 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 11.5.2+incompatible, 5.3.2-0.20260326202606-fac92f4a71f3 or later
```
go get github.com/mattermost/mattermost-server@v11.5.2+incompatible
```
github.com/mattermost/mattermost/server/v8 (Go): upgrade to 11.5.2, 8.0.0-20260326202606-fac92f4a71f3 or later
```
go get github.com/mattermost/mattermost/server/v8@v11.5.2
```

Technical details

A sensitive information disclosure vulnerability (CWE-200) exists in Mattermost Server due to improper sanitization of configuration fields during the generation of support packets. When a System Administrator generates a support packet via the System Console, the resulting file includes sensitive credentials in plaintext rather than masked or redacted values. An attacker with System Admin privileges, or an unauthorized party who gains access to a downloaded support packet, can extract these credentials to compromise connected services. The vulnerability is addressed by implementing 'FakeSetting' logic to mask sensitive keys during the packet generation process. Patches are available in versions 11.5.2, 11.4.4, and 10.11.14.

Affected products

Mattermost Mattermost Server 11.5.0 - 11.5.1, 11.4.0 - 11.4.3, 10.11.0 - 10.11.13, < 8.0.0-20260326202606-fac92f4a71f3

Identifiers

CVE-2026-6346
GHSA-9p64-jpc7-m2rp
GO-2026-5293

Timeline

2026-05-18: disclosed
2026-05-18: advisory
2026-06-01: other: Advisory reviewed and updated

References

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