# CVE-2026-4858: Mattermost path traversal in integration action URL

Source: https://junglewise.ai/threats/cve-2026-4858-mattermost-path-traversal-in-integration-action-url  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-21. Updated: 2026-06-23  
License: CC BY 4.0 with a link back

CVE-2026-4858 · Severity: high · CVSS 8 · Published 2026-05-21

Mattermost, a collaboration and messaging platform, contains a security flaw in how it handles integration URLs. A malicious user with a standard account could exploit this to perform actions as a system administrator, potentially leading to full control over the platform and access to sensitive corporate communications. Organizations should update to the latest patched versions to prevent unauthorized administrative access.

Technologies: [github.com/mattermost/mattermost-server (Go)](https://junglewise.ai/threats/technologies/github-com-mattermost-mattermost-server), [Mattermost Server](https://junglewise.ai/threats/technologies/server-public). Vendors: [Go](https://junglewise.ai/threats/vendors/go), [Mattermost](https://junglewise.ai/threats/vendors/mattermost).

## Quick answers

**Is CVE-2026-4858 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-4858 being exploited in the wild.

**How severe is CVE-2026-4858?** High severity, with a CVSS score of 8, published 21 May 2026.

**Which products and versions are affected?** github.com/mattermost/mattermost-server (Go) SEMVER:introduced=10.11.0+incompatible,fixed=10.11.15+incompatible,introduced=11.4.0+incompatible,fixed=11.4.5+incompatible,introduced=11.5.0+incompatible,fixed=11.5.4+incompatible,introduced=11.6.0+incompatible,fixed=11.6.1+incompatible, SEMVER:introduced=11.6.0,fixed=11.6.1; Mattermost Server 11.6.0, 11.5.0 to 11.5.3, 11.4.0 to 11.4.4, 10.11.0 to 10.11.14, 11.6.0, 11.5.0-11.5.3, 11.4.0-11.4.4, 10.11.0-10.11.14.

**Is there a fix for CVE-2026-4858?** Yes. github.com/mattermost/mattermost-server (Go): upgrade to 11.6.1, 11.6.1+incompatible or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-4858 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-4858?** Check whether you run github.com/mattermost/mattermost-server (Go) or Mattermost Server at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/mattermost/mattermost-server (Go): upgrade to 11.6.1, 11.6.1+incompatible or later

  ```sh
  go get github.com/mattermost/mattermost-server@v11.6.1+incompatible
  ```


## Technical details

A path traversal vulnerability (CWE-22) exists in Mattermost Server's handling of integration action URLs. The application fails to properly validate or sanitize these URLs, allowing a malicious authenticated user to inject traversal sequences. By doing so, the attacker can redirect requests to internal API endpoints. Because these requests may be processed using a system administrator's authentication token, the attacker can achieve a privilege escalation to call arbitrary administrative APIs. The exploit requires low privileges but involves high complexity and some user interaction. Patches are available in versions 11.6.1, 11.5.4, 11.4.5, and 10.11.15.

## Affected products

- Mattermost Mattermost Server 11.6.0, 11.5.0 to 11.5.3, 11.4.0 to 11.4.4, 10.11.0 to 10.11.14

## Identifiers

- CVE-2026-4858
- GHSA-c4r7-j7pp-r8mp
- GO-2026-5311

## Timeline

- 2026-05-21: disclosed
- 2026-05-21: advisory
- 2026-06-23: patched

## References

- [https://mattermost.com/security-updates](https://mattermost.com/security-updates)

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