Medium
Guest user can upload files without permission across teams
Type: advisorySources: OSV
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to validate team-specific upload_file permissions which allows a guest user to post files in channels where they lack upload_file permission via uploading files in a team where they have permission and reusing the file metadata in a POST request to a different team. Mattermost Advisory ID: MMSA-2025-00553
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-4265
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 3 Nov 2026, 15:31 UTC · Revision 1
Source evidence
Guest user can upload files without permission across teams
core-osv · Original sourcePublished 16 Mar 2026, 12:07 UTC
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to validate team-specific upload_file permissions which allows a guest user to post files in channels where they lack upload_file permission via uploading files in a team where they have permission and reusing the file metadata in a POST request to a different team. Mattermost Advisory ID: MMSA-2025-00553
osv:CVE-2026-4265
Complete source record
{
"id": "94d52306d59fde11538b5a3120b0a06393a43729d6322fea51920aada6a91185",
"url": "https://osv.dev/vulnerability/CVE-2026-4265",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "Guest user can upload files without permission across teams",
"summary": "Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to validate team-specific upload_file permissions which allows a guest user to post files in channels where they lack upload_file permission via uploading files in a team where they have permission and reusing the file metadata in a POST request to a different team. Mattermost Advisory ID: MMSA-2025-00553",
"evidence": "osv:CVE-2026-4265",
"products": [],
"severity": "medium",
"structured": {
"id": "CVE-2026-4265",
"aliases": [
"CVE-2026-4265",
"GHSA-xpvf-6qcc-9jqc",
"GO-2026-4749"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/mattermost/mattermost",
"type": "GIT",
"events": [
{
"introduced": "5b955468ea1ea8b56c0fb10feb258a36a767d7bb"
},
{
"fixed": "fddd4a70bcb32eaff394a2fa5399efcd1b2ae251"
},
{
"introduced": "ab7b138824c61fe1fe815243d7e2a914dec49c8b"
},
{
"fixed": "005521aa79666e6960bc3302f6172b810f6bff3a"
},
{
"introduced": "d27a2195068ddfa3ce17cf470f9739e4edb94b83"
},
{
"fixed": "4082c3dcf285e4d1a386d2ef37f14f39dc5a0094"
}
],
"database_specific": {
"extracted_events": [
{
"cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "10.11.0"
},
{
"fixed": "10.11.11"
}
],
"source": "CPE_RANGE"
},
{
"cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "11.2.0"
},
{
"fixed": "11.2.3"
}
],
"source": "CPE_RANGE"
},
{
"cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "11.3.0"
},
{
"fixed": "11.3.1"
}
],
"source": "CPE_RANGE"
}
]
}
}
],
"versions": [
"v10.11.11-rc1",
"v11.3.1-rc1",
"v10.11.10",
"v11.2.2",
"v11.3.0-rc4",
"v11.3.0-rc3",
"v11.3.0",
"mattermost-redux@11.3.0",
"@mattermost/types@11.3.0",
"@mattermost/client@11.3.0",
"v10.11.9",
"v11.2.1",
"v11.2.1-rc1",
"v11.2.0",
"v10.11.9-rc1",
"v10.11.8",
"v10.11.7",
"v10.11.6",
"v10.11.5",
"v10.11.4-rc3",
"v10.11.4",
"v10.11.4-rc2",
"v10.11.4-rc1",
"v10.11.3",
"v10.11.2-rc2",
"v10.11.2",
"v10.11.2-rc1",
"v10.11.1",
"v10.11.1-rc1",
"v10.11.0-rc3",
"v10.11.0",
"mattermost-redux@10.11.0",
"@mattermost/types@10.11.0",
"@mattermost/client@10.11.0"
],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-4265.json"
}
}
],
"modified": "2026-10-28T02:30:29.930216223Z",
"provider": "osv",
"references": [
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/4xxx/CVE-2026-4265.json",
"https://mattermost.com/security-updates",
"https://nvd.nist.gov/vuln/detail/CVE-2026-4265"
],
"provider_metadata": {
"cwe_ids": [
"CWE-863"
],
"cna_assigner": "Mattermost",
"unresolved_ranges": [
{
"extracted_events": [
{
"range": [
{
"introduced": "11.3.0"
},
{
"last_affected": "11.3.0"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StandaloneSingleVersion"
}
]
},
{
"extracted_events": [
{
"range": [
{
"introduced": "11.2.0"
},
{
"last_affected": "11.2.2"
},
{
"introduced": "10.11.0"
},
{
"last_affected": "10.11.10"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StandardRange"
}
]
}
],
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/4xxx/CVE-2026-4265.json"
}
},
"related_cves": [
{
"value": "CVE-2026-4265",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 496851,
"published_at": "2026-03-16T12:07:14.659+00:00"
}