Answer in brief
CVE-2026-6673 records a Medium severity (CVSS 6.4) vulnerability in Mattermost doesn't authenticate Atlassian Connect installed callbacks, allowing a remote unauthenticated attacker to inject a rogue sharedSecret. The current sources do not mark it as known exploited. The current feed maps github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 6.4. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| github.com/mattermost/mattermost-servergo | >=11.7.0,<11.7.1 | 11.7.1 |
| github.com/mattermost/mattermost-servergo | >=11.6.0,<11.6.3 | 11.6.3 |
| github.com/mattermost/mattermost-servergo | >=11.5.0,<11.5.6 | 11.5.6 |
| github.com/mattermost/mattermost-servergo | >=10.11.0,<10.11.18 | 10.11.18 |
Published upstream
Jun 22, 2026
Evidence: source:ghsa:source_dates:source-dates:recordSource modified
Sep 15, 2026
Evidence: source:ghsa:source_dates:source-dates:recordFirst seen by HOL
Jun 22, 2026
Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to authenticate Atlassian Connect installed callbacks, allowing a remote unauthenticated attacker to inject a rogue sharedSecret and disrupt the Jira integration via POST to /ac/installed during the pending-install window.. Mattermost Advisory ID: MMSA-2026-00654
Quoted source text, attributed separately from HOL analysis.