What is CVE-2026-3433?

CVE-2026-3433 is a medium-severity security vulnerability in github.com/mattermost/mattermost-server (go), affecting versions = 11.6.0. It is fixed in 11.6.1, 11.5.5, 10.11.17, 8.0.0-20260504071740-9408b98025d7.

How severe is CVE-2026-3433?

CVE-2026-3433 has a CVSS score of 4.3 (Medium). 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.

Which packages are affected by CVE-2026-3433?

github.com/mattermost/mattermost-server (go) versions = 11.6.0; github.com/mattermost/mattermost/server/v8 (go) versions >= 8.0.0-20250731163400-5b955468ea1e, < 8.0.0-20260504071740-9408b98025d7.

Is CVE-2026-3433 exploitable, and should I be worried?

Whether CVE-2026-3433 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.

What actually determines whether CVE-2026-3433 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.

CVE-2026-3433

Q: Is there a fix for CVE-2026-3433?

Yes. CVE-2026-3433 is fixed in 11.6.1, 11.5.5, 10.11.17, 8.0.0-20260504071740-9408b98025d7. Upgrade to this version or later.

Q: Is CVE-2026-3433 exploitable, and should I be worried?

Whether CVE-2026-3433 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.

Q: What actually determines whether CVE-2026-3433 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.

Q: How do I fix CVE-2026-3433?

Upgrade: github.com/mattermost/mattermost-server to 11.6.1 or later, github.com/mattermost/mattermost-server to 11.5.5 or later, github.com/mattermost/mattermost-server to 10.11.17 or later, github.com/mattermost/mattermost/server/v8 to 8.0.0-20260504071740-9408b98025d7 or later.

Summary

Mattermost doesn't restrict role_updated websocket event broadcasts to members of the affected team or channel

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to restrict role_updated websocket event broadcasts to members of the affected team or channel, which allows an authenticated attacker with guest-level access to observe permission scheme change notifications for private teams they are not a member of via the websocket connection. Mattermost Advisory ID: MMSA-2026-00616

Impact

CVE-2026-3433 has a CVSS score of 4.3 (Medium). The vector is network-reachable, low 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 (11.6.1, 11.5.5, 10.11.17, 8.0.0-20260504071740-9408b98025d7); upgrading removes the vulnerable code path.

Affected versions

github.com/mattermost/mattermost-server (= 11.6.0) github.com/mattermost/mattermost-server (>= 11.5.0, <= 11.5.4) github.com/mattermost/mattermost-server (>= 10.11.0, <= 10.11.15) github.com/mattermost/mattermost/server/v8 (>= 8.0.0-20250731163400-5b955468ea1e, < 8.0.0-20260504071740-9408b98025d7)

Security releases

github.com/mattermost/mattermost-server → 11.6.1 (go) github.com/mattermost/mattermost-server → 11.5.5 (go) github.com/mattermost/mattermost-server → 10.11.17 (go) github.com/mattermost/mattermost/server/v8 → 8.0.0-20260504071740-9408b98025d7 (go)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

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Remediation advice

Upgrade the following packages to resolve this vulnerability:

github.com/mattermost/mattermost-server to 11.6.1 or later; github.com/mattermost/mattermost-server to 11.5.5 or later; github.com/mattermost/mattermost-server to 10.11.17 or later; github.com/mattermost/mattermost/server/v8 to 8.0.0-20260504071740-9408b98025d7 or later

Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.

Frequently Asked Questions

What is CVE-2026-3433? CVE-2026-3433 is a medium-severity security vulnerability in github.com/mattermost/mattermost-server (go), affecting versions = 11.6.0. It is fixed in 11.6.1, 11.5.5, 10.11.17, 8.0.0-20260504071740-9408b98025d7.
How severe is CVE-2026-3433? CVE-2026-3433 has a CVSS score of 4.3 (Medium). 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.
Which packages are affected by CVE-2026-3433?
- github.com/mattermost/mattermost-server (go) (versions = 11.6.0)
- github.com/mattermost/mattermost/server/v8 (go) (versions >= 8.0.0-20250731163400-5b955468ea1e, < 8.0.0-20260504071740-9408b98025d7)
Is there a fix for CVE-2026-3433? Yes. CVE-2026-3433 is fixed in 11.6.1, 11.5.5, 10.11.17, 8.0.0-20260504071740-9408b98025d7. Upgrade to this version or later.
Is CVE-2026-3433 exploitable, and should I be worried? Whether CVE-2026-3433 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
What actually determines whether CVE-2026-3433 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.
How do I fix CVE-2026-3433?
- Upgrade github.com/mattermost/mattermost-server to 11.6.1 or later
- Upgrade github.com/mattermost/mattermost-server to 11.5.5 or later
- Upgrade github.com/mattermost/mattermost-server to 10.11.17 or later
- Upgrade github.com/mattermost/mattermost/server/v8 to 8.0.0-20260504071740-9408b98025d7 or later