CVE-2026-4273

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to validate that the RefreshedToken differs from the original invite token during remote cluster invite confirmation which allows an authenticated attacker to bypass token rotation and reuse the original invite token via sending a crafted invite confirmation with a RefreshedToken matching the original token. Mattermost Advisory ID: MMSA-2026-00575

The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.

CVE-2026-4273 has a CVSS score of 3.7 (Low). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (11.5.2, 10.11.14, 8.0.0-20260313190740-742e0be95074, 5.3.2-0.20260313190740-742e0be95074); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-4273? CVE-2026-4273 is a low-severity incorrect authorization vulnerability in github.com/mattermost/mattermost/server/v8 (go), affecting versions >= 11.5.0, < 11.5.2. It is fixed in 11.5.2, 10.11.14, 8.0.0-20260313190740-742e0be95074, 5.3.2-0.20260313190740-742e0be95074. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
2. How severe is CVE-2026-4273? CVE-2026-4273 has a CVSS score of 3.7 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-4273?
   • github.com/mattermost/mattermost/server/v8 (go) (versions >= 11.5.0, < 11.5.2)
   • github.com/mattermost/mattermost-server (go) (versions < 5.3.2-0.20260313190740-742e0be95074)
4. Is there a fix for CVE-2026-4273? Yes. CVE-2026-4273 is fixed in 11.5.2, 10.11.14, 8.0.0-20260313190740-742e0be95074, 5.3.2-0.20260313190740-742e0be95074. Upgrade to this version or later.
5. Is CVE-2026-4273 exploitable, and should I be worried? Whether CVE-2026-4273 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-4273 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-4273?
   • Upgrade github.com/mattermost/mattermost/server/v8 to 11.5.2 or later
   • Upgrade github.com/mattermost/mattermost/server/v8 to 10.11.14 or later
   • Upgrade github.com/mattermost/mattermost/server/v8 to 8.0.0-20260313190740-742e0be95074 or later
   • Upgrade github.com/mattermost/mattermost-server to 5.3.2-0.20260313190740-742e0be95074 or later