What is CVE-2026-2457?

CVE-2026-2457 is a medium-severity security vulnerability in github.com/mattermost/mattermost/server/v8 (go), affecting versions < 8.0.0-20260123211116-9efe617be8b8. It is fixed in 8.0.0-20260123211116-9efe617be8b8, 5.3.2-0.20260123211116-9efe617be8b8, 10.11.11, 11.2.3, 11.3.1.

How severe is CVE-2026-2457?

CVE-2026-2457 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.

Is CVE-2026-2457 exploitable, and should I be worried?

Whether CVE-2026-2457 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-2026-2457 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-2026-2457 in github.com/mattermost/mattermost/server/v8 | Intelligent Application Security

Q: How severe is CVE-2026-2457?

CVE-2026-2457 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.

Q: Which packages are affected by CVE-2026-2457?

github.com/mattermost/mattermost/server/v8 (go) versions < 8.0.0-20260123211116-9efe617be8b8; github.com/mattermost/mattermost-server (go) versions < 5.3.2-0.20260123211116-9efe617be8b8.

Q: Is there a fix for CVE-2026-2457?

Yes. CVE-2026-2457 is fixed in 8.0.0-20260123211116-9efe617be8b8, 5.3.2-0.20260123211116-9efe617be8b8, 10.11.11, 11.2.3, 11.3.1. Upgrade to this version or later.

Q: Is CVE-2026-2457 exploitable, and should I be worried?

Whether CVE-2026-2457 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-2026-2457 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-2026-2457?

Upgrade: github.com/mattermost/mattermost/server/v8 to 8.0.0-20260123211116-9efe617be8b8 or later, github.com/mattermost/mattermost-server to 5.3.2-0.20260123211116-9efe617be8b8 or later, github.com/mattermost/mattermost-server to 10.11.11 or later, github.com/mattermost/mattermost-server to 11.2.3 or later, github.com/mattermost/mattermost-server to 11.3.1 or later.

Summary

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to sanitize client-supplied post metadata which allows an authenticated attacker to spoof permalink embeds impersonating other users via crafted PUT requests to the post update API endpoint. Mattermost Advisory ID: MMSA-2025-00569

Impact

CVE-2026-2457 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 (8.0.0-20260123211116-9efe617be8b8, 5.3.2-0.20260123211116-9efe617be8b8, 10.11.11, 11.2.3, 11.3.1); upgrading removes the vulnerable code path.

Affected versions

github.com/mattermost/mattermost/server/v8 (< 8.0.0-20260123211116-9efe617be8b8) github.com/mattermost/mattermost-server (< 5.3.2-0.20260123211116-9efe617be8b8) github.com/mattermost/mattermost-server (>= 10.11.0-rc1, < 10.11.11) github.com/mattermost/mattermost-server (>= 11.2.0-rc1, < 11.2.3) github.com/mattermost/mattermost-server (>= 11.3.0-rc1, < 11.3.1)

Security releases

github.com/mattermost/mattermost/server/v8 → 8.0.0-20260123211116-9efe617be8b8 (go) github.com/mattermost/mattermost-server → 5.3.2-0.20260123211116-9efe617be8b8 (go) github.com/mattermost/mattermost-server → 10.11.11 (go) github.com/mattermost/mattermost-server → 11.2.3 (go) github.com/mattermost/mattermost-server → 11.3.1 (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.

See it in your environment

Remediation advice

Upgrade the following packages to resolve this vulnerability:

github.com/mattermost/mattermost/server/v8 to 8.0.0-20260123211116-9efe617be8b8 or later; github.com/mattermost/mattermost-server to 5.3.2-0.20260123211116-9efe617be8b8 or later; github.com/mattermost/mattermost-server to 10.11.11 or later; github.com/mattermost/mattermost-server to 11.2.3 or later; github.com/mattermost/mattermost-server to 11.3.1 or later

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

Frequently Asked Questions

What is CVE-2026-2457? CVE-2026-2457 is a medium-severity security vulnerability in github.com/mattermost/mattermost/server/v8 (go), affecting versions < 8.0.0-20260123211116-9efe617be8b8. It is fixed in 8.0.0-20260123211116-9efe617be8b8, 5.3.2-0.20260123211116-9efe617be8b8, 10.11.11, 11.2.3, 11.3.1.
How severe is CVE-2026-2457? CVE-2026-2457 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-2026-2457?
- github.com/mattermost/mattermost/server/v8 (go) (versions < 8.0.0-20260123211116-9efe617be8b8)
- github.com/mattermost/mattermost-server (go) (versions < 5.3.2-0.20260123211116-9efe617be8b8)
Is there a fix for CVE-2026-2457? Yes. CVE-2026-2457 is fixed in 8.0.0-20260123211116-9efe617be8b8, 5.3.2-0.20260123211116-9efe617be8b8, 10.11.11, 11.2.3, 11.3.1. Upgrade to this version or later.
Is CVE-2026-2457 exploitable, and should I be worried? Whether CVE-2026-2457 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-2026-2457 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-2026-2457?
- Upgrade github.com/mattermost/mattermost/server/v8 to 8.0.0-20260123211116-9efe617be8b8 or later
- Upgrade github.com/mattermost/mattermost-server to 5.3.2-0.20260123211116-9efe617be8b8 or later
- Upgrade github.com/mattermost/mattermost-server to 10.11.11 or later
- Upgrade github.com/mattermost/mattermost-server to 11.2.3 or later
- Upgrade github.com/mattermost/mattermost-server to 11.3.1 or later

Other vulnerabilities in github.com/mattermost/mattermost/server/v8

CVE-2026-4915 CVE-2026-5740 CVE-2026-4055 CVE-2026-5163 CVE-2026-6343