CVE-2026-4053: Github.com/mattermost/mattermost server Remote Code Execution Vulnerability

LOW
Advisory Identifier: GHSA-hw87-6jcq-9f8q
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CVSS 3.1
CWE-672
Published
Advisory Summary

CVE-2026-4053 is a LOW (CVSS 3.1) remote code execution vulnerability (CWE-672: Operation on a Resource after Expiration or Release) affecting Github.com/mattermost/mattermost server libraries in the Go ecosystem. The issue involves mattermost doesn't enforce the postedittimelimit on non-message post fields. Remediation is available by upgrading affected packages to version 11.5.2, 0.0.0-20260414103857-b21ef302025e.

CVE-2026-4053 at a Glance

CVE Identifier CVE-2026-4053
GHSA Identifier GHSA-hw87-6jcq-9f8q
Severity LOW
CVSS v3.1 Base Score 3.1
CWE Classification CWE-672: Operation on a Resource after Expiration or Release
Affected Product Github.com/mattermost/mattermost server
Package Ecosystem Go
Published Date
Last Updated

Security Impact

CVSS: 3.1

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-4053

To remediate this vulnerability, upgrade all affected Github.com/mattermost/mattermost server dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/mattermost/mattermost-server fixed: 11.5.2 
Upgrade github.com/mattermost/mattermost-server to 11.5.2
github.com/mattermost/mattermost-server fixed: 0.0.0-20260414103857-b21ef302025e 
Upgrade github.com/mattermost/mattermost-server to 0.0.0-20260414103857-b21ef302025e
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/mattermost/mattermost-server

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-4053, inspect your project dependencies for Github.com/mattermost/mattermost server:

inspect dependencies for github.com/mattermost/mattermost-server

Analyze the terminal output to locate any version of Github.com/mattermost/mattermost server in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 11.5.2), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-672: Operation on a Resource after Expiration or Release, where the product uses, accesses, or otherwise operates on a resource after that resource has been expired, released, or revoked. In Github.com/mattermost/mattermost server, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to enforce the PostEditTimeLimit on non-message post fields which allows an authenticated user to modify post file attachments, props, and pin status after the edit window has expired via the post patch and update API endpoints. Mattermost Advisory ID: MMSA-2026-00631.

CVE-2026-4053 Affected Github.com/mattermost/mattermost server Versions

2 component(s)
Fixed Versions:
11.5.20.0.0-20260414103857-b21ef302025e
Product / Package Ecosystem Affected Versions Fixed Version
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
≥ 11.5.0
< 11.5.2
11.5.2
github.com/mattermost/mattermost-server
golang/github.com/mattermost/mattermost-server
Go
≥ 0.0.0-20250731163400-5b955468ea1e
< 0.0.0-20260414103857-b21ef302025e
0.0.0-20260414103857-b21ef302025e

References

NVD — CVE-2026-4053 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-4053
Github.com/mattermost/mattermost server Source Repository REPOSITORY
https://github.com/mattermost/mattermost
Github.com/mattermost/mattermost server Security Information SECURITY
https://mattermost.com/security-updates

Frequently Asked Questions

What is CVE-2026-4053?
CVE-2026-4053 is a security vulnerability in Github.com/mattermost/mattermost server involving Mattermost doesn't enforce the PostEditTimeLimit on non-message post fields under CWE-672: Operation on a Resource after Expiration or Release.
Which Github.com/mattermost/mattermost server versions are affected?
Affected versions include releases prior to 11.5.2, 0.0.0-20260414103857-b21ef302025e across affected packages: github.com/mattermost/mattermost-server.
What version fixes CVE-2026-4053?
Upgrading to 11.5.2, 0.0.0-20260414103857-b21ef302025e (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/mattermost/mattermost-server affected?
Yes, github.com/mattermost/mattermost-server is affected in releases prior to 11.5.2, 0.0.0-20260414103857-b21ef302025e. Upgrade your dependency to 11.5.2, 0.0.0-20260414103857-b21ef302025e or later.
What is the CVSS score of CVE-2026-4053?
CVE-2026-4053 has a CVSS v3.1 base score of 3.1 (LOW) with vector string CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N.
What CWE is associated with CVE-2026-4053?
CVE-2026-4053 is classified under CWE-672: Operation on a Resource after Expiration or Release (The product uses, accesses, or otherwise operates on a resource after that resource has been expired, released, or revoked.).
How can I check Go dependencies for CVE-2026-4053?
Run the dependency tree command: 'inspect dependencies for github.com/mattermost/mattermost-server'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-hw87-6jcq-9f8q",
  "modified" : "2026-05-28T19:26:24Z",
  "published" : "2026-05-15T21:31:33Z",
  "aliases" : [ "CVE-2026-4053" ],
  "summary" : "Mattermost doesn't enforce the PostEditTimeLimit on non-message post fields",
  "details" : "Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to enforce the PostEditTimeLimit on non-message post fields which allows an authenticated user to modify post file attachments, props, and pin status after the edit window has expired via the post patch and update API endpoints. Mattermost Advisory ID: MMSA-2026-00631.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "11.5.0"
      }, {
        "fixed" : "11.5.2"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.0.0-20250731163400-5b955468ea1e"
      }, {
        "fixed" : "0.0.0-20260414103857-b21ef302025e"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-4053"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mattermost/mattermost"
  }, {
    "type" : "WEB",
    "url" : "https://mattermost.com/security-updates"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-672" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-28T19:26:24Z",
    "nvd_published_at" : "2026-05-15T19:17:04Z"
  }
}