CVE-2026-20719: Mattermost Denial of Service Vulnerability
MODERATECVE-2026-20719 is a MODERATE (CVSS 4.3) denial of service vulnerability (CWE-754: Improper Check for Unusual or Exceptional Conditions) affecting Mattermost libraries in the Go ecosystem. The issue involves authenticated dos through failure to prevent rendering of external svgs on link embeds. Remediation is available by upgrading affected packages to version 11.4.1, 11.3.2, 11.2.4, 8.0.0-20260217110922-b7d4a1f1f59b, 10.11.2.
CVE-2026-20719 at a Glance
Security Impact
CVSS: 4.3
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L).
How to Fix CVE-2026-20719
To remediate this vulnerability, upgrade all affected Mattermost 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/v8 to 11.4.1Upgrade github.com/mattermost/mattermost/server/v8 to 11.3.2Upgrade github.com/mattermost/mattermost/server/v8 to 11.2.4Upgrade github.com/mattermost/mattermost/server/v8 to 8.0.0-20260217110922-b7d4a1f1f59bUpgrade github.com/mattermost/mattermost/server/v8 to 10.11.2Run 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/v8How to Check if You Are Affected
To determine whether your application is affected by CVE-2026-20719, inspect your project dependencies for Mattermost:
inspect dependencies for github.com/mattermost/mattermost/server/v8Analyze the terminal output to locate any version of Mattermost in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 11.4.1), 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-754: Improper Check for Unusual or Exceptional Conditions, where the product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product. In Mattermost, 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-2026-20719 Affected Mattermost Versions
5 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/mattermost/mattermost/server/v8
|
Go |
≥ 11.4.0-rc1
< 11.4.1
|
11.4.1
|
|
github.com/mattermost/mattermost/server/v8
|
Go |
≥ 11.3.0-rc1
< 11.3.2
|
11.3.2
|
|
github.com/mattermost/mattermost/server/v8
|
Go |
≥ 11.2.0-rc1
< 11.2.4
|
11.2.4
|
|
github.com/mattermost/mattermost/server/v8
|
Go |
≥ 8.0.0-20260105080200-d27a2195068d
< 8.0.0-20260217110922-b7d4a1f1f59b
|
8.0.0-20260217110922-b7d4a1f1f59b
|
|
github.com/mattermost/mattermost/server/v8
|
Go |
≥ 10.11.0-rc1
< 10.11.2
|
10.11.2
|
References
Frequently Asked Questions
What is CVE-2026-20719?
Which Mattermost versions are affected?
What version fixes CVE-2026-20719?
Is github.com/mattermost/mattermost/server/v8 affected?
What is the CVSS score of CVE-2026-20719?
What CWE is associated with CVE-2026-20719?
How can I check Go dependencies for CVE-2026-20719?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-86vc-mg26-fj6x",
"modified" : "2026-03-30T22:21:55Z",
"published" : "2026-03-25T18:31:48Z",
"aliases" : [ "CVE-2026-20719" ],
"summary" : "Mattermost: Authenticated DoS through failure to prevent rendering of external SVGs on link embeds ",
"details" : "Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to prevent rendering of external SVGs on link embeds which allows unauthenticated users to crash the Mattermost webapp and desktop app via creating an issue or PR on GitHub. Mattermost Advisory ID: MMSA-2026-00595",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost/server/v8"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.4.0-rc1"
}, {
"fixed" : "11.4.1"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost/server/v8"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.3.0-rc1"
}, {
"fixed" : "11.3.2"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost/server/v8"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "11.2.0-rc1"
}, {
"fixed" : "11.2.4"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost/server/v8"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "8.0.0-20260105080200-d27a2195068d"
}, {
"fixed" : "8.0.0-20260217110922-b7d4a1f1f59b"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/mattermost/mattermost/server/v8"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "10.11.0-rc1"
}, {
"fixed" : "10.11.2"
} ]
} ]
} ],
"references" : [ {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-20719"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/mattermost/mattermost"
}, {
"type" : "WEB",
"url" : "https://mattermost.com/security-updates"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-754" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-03-30T22:21:55Z",
"nvd_published_at" : "2026-03-25T17:16:30Z"
}
}