CVE-2026-4635: Github.com/mattermost/mattermost server Mattermost Doesn't Archive The Channel Vulnerability
MODERATECVE-2026-4635 is a MODERATE (CVSS 5.3) mattermost doesn't archive the channel vulnerability (CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')) affecting Github.com/mattermost/mattermost server libraries in the Go ecosystem. The issue involves mattermost doesn't archive the channel before removing persistent notifications. Remediation is available by upgrading affected packages to version 11.6.1, 11.5.4, 11.4.5, 10.11.15.
CVE-2026-4635 at a Glance
Security Impact
CVSS: 5.3
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:N/A:H).
How to Fix CVE-2026-4635
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.
Upgrade github.com/mattermost/mattermost-server to 11.6.1Upgrade github.com/mattermost/mattermost-server to 11.5.4Upgrade github.com/mattermost/mattermost-server to 11.4.5Upgrade github.com/mattermost/mattermost-server to 10.11.15Run the following command in your project directory to verify that all resolved dependencies use the patched release:
inspect dependencies for github.com/mattermost/mattermost-serverHow to Check if You Are Affected
To determine whether your application is affected by CVE-2026-4635, inspect your project dependencies for Github.com/mattermost/mattermost server:
inspect dependencies for github.com/mattermost/mattermost-serverAnalyze 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 11.6.1), 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-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition'), where the product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently. 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
CVE-2026-4635 Affected Github.com/mattermost/mattermost server Versions
4 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 11.6.0
< 11.6.1
All 1 versions
11.6.0
|
11.6.1
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 11.5.0
< 11.5.4
|
11.5.4
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 11.4.0
< 11.4.5
|
11.4.5
|
|
github.com/mattermost/mattermost-server
|
Go |
≥ 10.11.0
< 10.11.15
|
10.11.15
|
References
Frequently Asked Questions
What is CVE-2026-4635?
Which Github.com/mattermost/mattermost server versions are affected?
What version fixes CVE-2026-4635?
Is github.com/mattermost/mattermost-server affected?
What is the CVSS score of CVE-2026-4635?
What CWE is associated with CVE-2026-4635?
How can I check Go dependencies for CVE-2026-4635?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-pg7c-462j-grxv",
"modified" : "2026-06-26T22:48:42Z",
"published" : "2026-05-26T13:30:15Z",
"aliases" : [ "CVE-2026-4635" ],
"summary" : "Mattermost doesn't archive the channel before removing persistent notifications",
"details" : "Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to archive the channel before removing persistent notifications which allows authenticated user to crash the server via timing the creation of persistent notification message between the server deleting existing persistent notifications and archiving the channel. Mattermost Advisory ID: MMSA-2026-00637.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.6.0"
}, {
"fixed" : "11.6.1"
} ]
} ],
"versions" : [ "11.6.0" ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.5.0"
}, {
"fixed" : "11.5.4"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.4.0"
}, {
"fixed" : "11.4.5"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "10.11.0"
}, {
"fixed" : "10.11.15"
} ]
} ]
} ],
"references" : [ {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-4635"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/mattermost/mattermost"
}, {
"type" : "WEB",
"url" : "https://mattermost.com/security-updates"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-362" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-06-26T22:48:42Z",
"nvd_published_at" : "2026-05-22T11:16:22Z"
}
}