CVE-2026-9816 (GCVE-0-2026-9816)
Vulnerability from cvelistv5 – Published: 2026-08-17 22:05 – Updated: 2026-08-17 22:05
VLAI
EPSS
VEX
Title
Insufficient server-side validation of board member role fields permits privilege escalation
Summary
Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate BoardMember.Scheme* fields server-side on insert and archive-import paths which allows a board editor or non-guest team member to grant board admin to arbitrary users via POST /api/v2/boards/{boardID}/members and POST /api/v2/teams/{teamID}/archive/import.. Mattermost Advisory ID: MMSA-2026-00685
Severity
8.3 (High)
CWE
- CWE-863 - Incorrect Authorization
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:
11.7.0 , ≤ 11.7.6
(semver)
Affected: 10.11.0 , ≤ 10.11.21 (semver) Affected: 11.8.0 , ≤ 11.8.3 (semver) Unaffected: 11.9.0 Unaffected: 11.7.7 Unaffected: 10.11.22 Unaffected: 11.8.4 |
guessed |
{
"containers": {
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{
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"version": "11.7.7"
},
{
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"version": "10.11.22"
},
{
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"version": "11.8.4"
}
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}
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"value": "kamil-sawicki"
}
],
"descriptions": [
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}
],
"metrics": [
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"attackVector": "NETWORK",
"availabilityImpact": "HIGH",
"baseScore": 8.3,
"baseSeverity": "HIGH",
"confidentialityImpact": "LOW",
"integrityImpact": "HIGH",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H",
"version": "3.1"
},
"format": "CVSS",
"scenarios": [
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}
]
}
],
"problemTypes": [
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"descriptions": [
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"description": "CWE-863: Incorrect Authorization",
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}
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"providerMetadata": {
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"tags": [
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"url": "https://mattermost.com/security-updates"
}
],
"solutions": [
{
"lang": "en",
"value": "Update Mattermost to versions 11.9.0, 11.7.7, 10.11.22, 11.8.4 or higher."
}
],
"source": {
"advisory": "MMSA-2026-00685",
"defect": [
"https://mattermost.atlassian.net/browse/MM-69022"
],
"discovery": "EXTERNAL"
},
"title": "Insufficient server-side validation of board member role fields permits privilege escalation",
"x_generator": {
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}
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"cveMetadata": {
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"cveId": "CVE-2026-9816",
"datePublished": "2026-08-17T22:05:24.910Z",
"dateReserved": "2026-05-28T09:54:00.723Z",
"dateUpdated": "2026-08-17T22:05:24.910Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"epss": {
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"date": "2026-08-18",
"epss": "0.00245",
"percentile": "0.15997"
},
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}
}
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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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