Medium
Mattermost Server Algorithmic DoS via Unbounded Markdown Block Nesting
Type: advisorySources: OSV
Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.8, 10.11.x <= 10.11.22 fail to limit the nesting depth in the server-side Markdown parser which allows an authenticated attacker to cause a denial of service (CPU resource exhaustion) via a crafted post containing deeply nested blockquotes or list items.. Mattermost Advisory ID: MMSA-2026-00707
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-86349
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 4 Nov 2026, 13:24 UTC · Revision 1
Source evidence
Mattermost Server Algorithmic DoS via Unbounded Markdown Block Nesting
core-osv · Original sourcePublished 14 Sept 2026, 13:51 UTC
Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.8, 10.11.x <= 10.11.22 fail to limit the nesting depth in the server-side Markdown parser which allows an authenticated attacker to cause a denial of service (CPU resource exhaustion) via a crafted post containing deeply nested blockquotes or list items.. Mattermost Advisory ID: MMSA-2026-00707
osv:CVE-2026-86349
Complete source record
{
"id": "c16642dfa025756857a22d6009636c8a6349465d5fee3d3247ddfbec392804d1",
"url": "https://osv.dev/vulnerability/CVE-2026-86349",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "Mattermost Server Algorithmic DoS via Unbounded Markdown Block Nesting",
"summary": "Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.8, 10.11.x <= 10.11.22 fail to limit the nesting depth in the server-side Markdown parser which allows an authenticated attacker to cause a denial of service (CPU resource exhaustion) via a crafted post containing deeply nested blockquotes or list items.. Mattermost Advisory ID: MMSA-2026-00707",
"evidence": "osv:CVE-2026-86349",
"products": [],
"severity": "medium",
"structured": {
"id": "CVE-2026-86349",
"aliases": [
"CVE-2026-86349"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/mattermost/mattermost",
"type": "GIT",
"events": [
{
"introduced": "5b955468ea1ea8b56c0fb10feb258a36a767d7bb"
},
{
"fixed": "075d003e1391ff0b24eca1e63b0222eb46eaded6"
},
{
"introduced": "a9e574a82633915f22071f0d7ca2b006f249ec2a"
},
{
"fixed": "b706a013b7412947109e82d28971fda64e7c896b"
},
{
"introduced": "e8bd2b8a871cbeff6943bead62328478118188df"
},
{
"fixed": "d9c17e42b19c27dfac0ebe6840d954a41e626890"
},
{
"introduced": "583461af10fc9b2aef2871c722fc4376db695832"
},
{
"fixed": "1f738d345805168964a55e5860aac9c747dceb78"
}
],
"database_specific": {
"extracted_events": [
{
"cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "10.11.0"
},
{
"fixed": "10.11.23"
}
],
"source": "CPE_RANGE"
},
{
"cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "11.7.0"
},
{
"fixed": "11.7.9"
}
],
"source": "CPE_RANGE"
},
{
"cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "11.8.0"
},
{
"fixed": "11.8.5"
}
],
"source": "CPE_RANGE"
},
{
"cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "11.9.0"
},
{
"fixed": "11.9.1"
}
],
"source": "CPE_RANGE"
}
]
}
}
],
"versions": [
"v11.7.8",
"v11.8.4",
"v11.7.7",
"v10.11.22",
"v11.9.0",
"mattermost-redux@11.9.0",
"@mattermost/types@11.9.0",
"@mattermost/shared@11.9.0",
"@mattermost/client@11.9.0",
"v11.8.3",
"v10.11.21",
"v11.7.6",
"v11.8.2",
"v11.7.5-rc1",
"v11.7.5",
"v11.8.1",
"v11.7.4",
"v11.7.3",
"v10.11.20",
"v11.8.0-rc5",
"v11.8.0",
"mattermost-redux@11.8.0",
"@mattermost/types@11.8.0",
"@mattermost/shared@11.8.0",
"@mattermost/client@11.8.0",
"v10.11.19",
"v10.11.19-rc1",
"v11.7.2",
"v10.11.18",
"v11.7.1",
"v10.11.17",
"v10.11.16",
"v11.7.0",
"mattermost-redux@11.7.0",
"@mattermost/types@11.7.0",
"@mattermost/shared@11.7.0",
"@mattermost/client@11.7.0",
"v10.11.15-rc1",
"v10.11.15",
"v10.11.14",
"v10.11.14-rc1",
"v10.11.13",
"v10.11.13-rc1",
"v10.11.12",
"v10.11.11-rc2",
"v10.11.11",
"v10.11.11-rc1",
"v10.11.10",
"v10.11.9",
"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-2026-86349.json"
}
}
],
"modified": "2026-10-28T02:30:35.679114972Z",
"provider": "osv",
"references": [
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/86xxx/CVE-2026-86349.json",
"https://mattermost.com/security-updates",
"https://nvd.nist.gov/vuln/detail/CVE-2026-86349"
],
"provider_metadata": {
"cwe_ids": [
"CWE-407"
],
"cna_assigner": "Mattermost",
"unresolved_ranges": [
{
"extracted_events": [
{
"range": [
{
"introduced": "11.9.0"
},
{
"last_affected": "11.9.0"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StandaloneSingleVersion"
}
]
},
{
"extracted_events": [
{
"range": [
{
"introduced": "11.8.0"
},
{
"last_affected": "11.8.4"
},
{
"introduced": "11.7.0"
},
{
"last_affected": "11.7.8"
},
{
"introduced": "10.11.0"
},
{
"last_affected": "10.11.22"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StandardRange"
}
]
}
],
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/86xxx/CVE-2026-86349.json"
}
},
"related_cves": [
{
"value": "CVE-2026-86349",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 503052,
"published_at": "2026-09-14T13:51:30.175+00:00"
}