{
"id": "GHSA-8r89-8w26-cq32",
"aliases": [
"CVE-2026-5163"
],
"details": "Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint.. Mattermost Advisory ID: MMSA-2026-00645",
"summary": "Mattermost doesn't verify channel membership when processing AI-assisted message rewrites",
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "11.5.0"
},
{
"fixed": "11.5.2"
}
]
}
],
"package": {
"name": "github.com/mattermost/mattermost/server/v8",
"ecosystem": "Go"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "8.0.0-20260401090745-f4d1abe7e8f5"
}
]
}
],
"package": {
"name": "github.com/mattermost/mattermost/server/v8",
"ecosystem": "Go"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "5.3.2-0.20260401090745-f4d1abe7e8f5"
}
]
}
],
"package": {
"name": "github.com/mattermost/mattermost-server",
"ecosystem": "Go"
}
}
],
"modified": "2026-06-01T15:27:00Z",
"severity": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N"
}
],
"published": "2026-05-18T09:31:48Z",
"references": [
{
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-5163",
"type": "ADVISORY"
},
{
"url": "https://github.com/mattermost/mattermost/commit/f4d1abe7e8f545f1a87f463fa9fe451c731aebf8",
"type": "WEB"
},
{
"url": "https://github.com/mattermost/mattermost",
"type": "PACKAGE"
},
{
"url": "https://mattermost.com/security-updates",
"type": "WEB"
}
],
"schema_version": "1.4.0",
"database_specific": {
"cwe_ids": [
"CWE-862"
],
"severity": "MODERATE",
"github_reviewed": true,
"nvd_published_at": "2026-05-18T09:16:23Z",
"github_reviewed_at": "2026-06-01T15:27:00Z"
}
}