CVE-2026-27769
LOWCVE-2026-27769 is a low-severity (CVSS 2.7) CWE-862 vulnerability in github.com/mattermost/mattermost-server. O3 Security confirms whether CVE-2026-27769 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Connected Workspaces: Malicious remote server can manipulate arbitrary user's status
Blast Radius
github.com/mattermost/mattermost-serverReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Mattermost versions 10.11.x <= 10.11.12 fail to validate whether users were correctly owned by the correct Connected Workspace which allows a malicious remote server connected using the Conntexted Workspaces feature to change the displayed status of local users via the Connected Workspaces API.. Mattermost Advisory ID: MMSA-2026-00603
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 8.0.0-20250721062209-4952acea88ce&&< 8.0.0-20260316060126-bc1a2b34b1f9 | 8.0.0-20260316060126-bc1a2b34b1f9 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/mattermost/mattermost-server. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/mattermost/mattermost-server to 8.0.0-20260316060126-bc1a2b34b1f9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27769 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-27769 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-27769. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-27769 in your dependencies?
O3 detects CVE-2026-27769 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.