CVE-2026-86349 (GCVE-0-2026-86349)
Vulnerability from cvelistv5 – Published: 2026-09-14 13:51 – Updated: 2026-09-14 13:51
VLAI
EPSS
VEX
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
Severity
4.3 (Medium)
CWE
- CWE-407 - Inefficient Algorithmic Complexity
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://mattermost.com/security-updates | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Mattermost | Mattermost |
Affected:
11.9.0 , ≤ 11.9.0
(semver)
Affected: 11.8.0 , ≤ 11.8.4 (semver) Affected: 11.7.0 , ≤ 11.7.8 (semver) Affected: 10.11.0 , ≤ 10.11.22 (semver) Unaffected: 11.10.0 Unaffected: 11.9.1 Unaffected: 11.8.5 Unaffected: 11.7.9 Unaffected: 10.11.23 |
guessed |
{
"containers": {
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"product": "Mattermost",
"vendor": "Mattermost",
"versions": [
{
"lessThanOrEqual": "11.9.0",
"status": "affected",
"version": "11.9.0",
"versionType": "semver"
},
{
"lessThanOrEqual": "11.8.4",
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"version": "11.8.0",
"versionType": "semver"
},
{
"lessThanOrEqual": "11.7.8",
"status": "affected",
"version": "11.7.0",
"versionType": "semver"
},
{
"lessThanOrEqual": "10.11.22",
"status": "affected",
"version": "10.11.0",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "11.10.0"
},
{
"status": "unaffected",
"version": "11.9.1"
},
{
"status": "unaffected",
"version": "11.8.5"
},
{
"status": "unaffected",
"version": "11.7.9"
},
{
"status": "unaffected",
"version": "10.11.23"
}
]
}
],
"credits": [
{
"lang": "en",
"type": "finder",
"value": "tr66net"
}
],
"descriptions": [
{
"lang": "en",
"value": "Mattermost versions 11.9.x \u003c= 11.9.0, 11.8.x \u003c= 11.8.4, 11.7.x \u003c= 11.7.8, 10.11.x \u003c= 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"
}
],
"metrics": [
{
"cvssV3_1": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "LOW",
"baseScore": 4.3,
"baseSeverity": "MEDIUM",
"confidentialityImpact": "NONE",
"integrityImpact": "NONE",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L",
"version": "3.1"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-407",
"description": "CWE-407: Inefficient Algorithmic Complexity",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-09-14T13:51:30.175Z",
"orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee",
"shortName": "Mattermost"
},
"references": [
{
"name": "MMSA-2026-00707",
"tags": [
"vendor-advisory"
],
"url": "https://mattermost.com/security-updates"
}
],
"solutions": [
{
"lang": "en",
"value": "Update Mattermost to versions 11.10.0, 11.9.1, 11.8.5, 11.7.9, 10.11.23 or higher."
}
],
"source": {
"advisory": "MMSA-2026-00707",
"defect": [
"https://mattermost.atlassian.net/browse/MM-69398"
],
"discovery": "EXTERNAL"
},
"title": "Mattermost Server Algorithmic DoS via Unbounded Markdown Block Nesting",
"x_generator": {
"engine": "cvelib 1.8.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee",
"assignerShortName": "Mattermost",
"cveId": "CVE-2026-86349",
"datePublished": "2026-09-14T13:51:30.175Z",
"dateReserved": "2026-09-07T09:38:22.768Z",
"dateUpdated": "2026-09-14T13:51:30.175Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"nvd": "{\"cve\":{\"id\":\"CVE-2026-86349\",\"sourceIdentifier\":\"responsibledisclosure@mattermost.com\",\"published\":\"2026-09-14T14:17:15.687\",\"lastModified\":\"2026-09-14T14:17:15.687\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"Mattermost versions 11.9.x \u003c= 11.9.0, 11.8.x \u003c= 11.8.4, 11.7.x \u003c= 11.7.8, 10.11.x \u003c= 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\"}],\"affected\":[{\"source\":\"responsibledisclosure@mattermost.com\",\"affectedData\":[{\"vendor\":\"Mattermost\",\"product\":\"Mattermost\",\"defaultStatus\":\"unaffected\",\"versions\":[{\"version\":\"11.9.0\",\"lessThanOrEqual\":\"11.9.0\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"11.8.0\",\"lessThanOrEqual\":\"11.8.4\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"11.7.0\",\"lessThanOrEqual\":\"11.7.8\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"10.11.0\",\"lessThanOrEqual\":\"10.11.22\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"11.10.0\",\"status\":\"unaffected\"},{\"version\":\"11.9.1\",\"status\":\"unaffected\"},{\"version\":\"11.8.5\",\"status\":\"unaffected\"},{\"version\":\"11.7.9\",\"status\":\"unaffected\"},{\"version\":\"10.11.23\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"responsibledisclosure@mattermost.com\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L\",\"baseScore\":4.3,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"LOW\"},\"exploitabilityScore\":2.8,\"impactScore\":1.4}]},\"weaknesses\":[{\"source\":\"responsibledisclosure@mattermost.com\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-407\"}]}],\"references\":[{\"url\":\"https://mattermost.com/security-updates\",\"source\":\"responsibledisclosure@mattermost.com\"}]}}"
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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