{
"id": "GHSA-xvcx-mgpc-5xh3",
"aliases": [
"CVE-2026-6339"
],
"details": "Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636",
"summary": "Mattermost doesn't validate the X-Requested-With header on the burn-on-read reveal endpoint",
"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": "11.4.0"
},
{
"fixed": "11.4.4"
}
]
}
],
"package": {
"name": "github.com/mattermost/mattermost/server/v8",
"ecosystem": "Go"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "8.0.0-20260327001745-7a339a6438f5"
}
]
}
],
"package": {
"name": "github.com/mattermost/mattermost/server/v8",
"ecosystem": "Go"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "5.3.2-0.20260327001745-7a339a6438f5"
}
]
}
],
"package": {
"name": "github.com/mattermost/mattermost-server",
"ecosystem": "Go"
}
}
],
"modified": "2026-06-01T15:22:30Z",
"severity": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L"
}
],
"published": "2026-05-18T09:31:48Z",
"references": [
{
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-6339",
"type": "ADVISORY"
},
{
"url": "https://github.com/mattermost/mattermost/commit/7a339a6438f5a4a5feba6b8de887f17a1378b207",
"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-346"
],
"severity": "MODERATE",
"github_reviewed": true,
"nvd_published_at": "2026-05-18T09:16:23Z",
"github_reviewed_at": "2026-06-01T15:22:30Z"
}
}