# CVE-2025-12559: server — Fix Available 🐹 🐹 Go Not in CISA KEV MEDIUM severity # CVE-2025-12559 — server MEDIUM [Fix: mattermost/mattermost#34110](https://github.com/mattermost/mattermost/pull/34110) CVE-2025-12559 is a medium-severity (CVSS 4.3) Information Exposure vulnerability in github.com/mattermost/mattermost/server/v8. A fix is available for github.com/mattermost/mattermost/server/v8 — see the affected versions and patch details below. Information Disclosure in Common Teams API Also known as[GHSA-4g87-9x45-cx2h](/vulnerability/GHSA-4g87-9x45-cx2h)GO-2025-4169 Published Nov 27, 2025 Updated Oct 28, 2026 Affected 5 pkgs Patched 5 / 5 Exploits None indexed Exploitation data as of Nov 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS) ## Exploitation Status ### No confirmed exploitation observed yet - CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment. Exploitation and automatability from CISA’s SSVC triage for CVE-2025-12559. ## EPSS Exploitation Probability [via FIRST.org ↗](https://www.first.org/epss/) 0.2%probability of exploitation in next 30 days Lower Risk0.00% Lower risk than most CVEs14th percentile — riskier than 14% of all scored CVEsHighest risk 0.00%0.24%0.49%0.73%0.0%0.2%May 26Sep 26Nov 26 Probability of exploitation in the next 30 days, from [FIRST.org EPSS](https://www.first.org/epss/). ## How urgent is this, really ## Where this sits among everything scored ## Real-World Exposure 5 pkgs affected 🐹`github.com/mattermost/mattermost/server/v8`🐹`github.com/mattermost/mattermost-server`🐹`github.com/mattermost/mattermost-server`🐹`github.com/mattermost/mattermost-server`🐹`github.com/mattermost/mattermost-server` Real-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 11.0.x <= 11.0.2, 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12 fail to sanitize team email addresses to be visible only to Team Admins, which allows any authenticated user to view team email addresses via the GET /api/v4/channels/{channel\_id}/common\_teams endpoint ## Affected Packages 5 total 5 fixed Ecosystem Package Vulnerable range Fix 🐹Go `github.com/mattermost/mattermost/server/v8` all versions 8.0.0-20251015091448-abbf01b9db45`go get github.com/mattermost/mattermost/server/v8@v8.0.0-20251015091448-abbf01b9db45` 🐹Go `github.com/mattermost/mattermost-server` ≥ 11.0.0&&< 11.0.3 11.0.3`go get github.com/mattermost/mattermost-server@v11.0.3` 🐹Go `github.com/mattermost/mattermost-server` ≥ 10.12.0&&< 10.12.2 10.12.2`go get github.com/mattermost/mattermost-server@v10.12.2` 🐹Go `github.com/mattermost/mattermost-server` ≥ 10.11.0&&< 10.11.5 10.11.5`go get github.com/mattermost/mattermost-server@v10.11.5` 🐹Go `github.com/mattermost/mattermost-server` ≥ 10.5.0&&< 10.5.13 10.5.13`go get github.com/mattermost/mattermost-server@v10.5.13` ## Affected Products 1 product · 4 configurations Application `mattermost server`mattermost ≥ 11.0.0 && < 11.0.3 range ## Detection & mitigation playbook Open-source dependency 1. ### Detect Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/mattermost/mattermost/server/v8, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version. 2. ### Fix Update github.com/mattermost/mattermost/server/v8 to 8.0.0-20251015091448-abbf01b9db45 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-12559 is resolved across your whole dependency graph. 3. ### Workarounds Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them. ## Frequently Asked Questions Mattermost versions 11.0.x <= 11.0.2, 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12 fail to sanitize team email addresses to be visible only to Team Admins, which allows any authenticated user to view team email addresses via the GET /api/v4/channels/{channel\_id}/common\_teams endpoint O3 Security · Impact-Aware SCA ### Is CVE-2025-12559 in your dependencies? Find it across Go, including transitive dependencies. [Scan my dependencies](/book-demo) [How O3 SCA works](/impact-aware-sca)