CVE-2026-95666
📛 CVE Title
Unbounded post ID array in the bulk reactions endpoint allows denial of service
Description
Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to limit the length of the post ID array accepted by the bulk reactions endpoint which allows an authenticated user to cause excessive database load via a crafted request to {{POST /api/v4/posts/ids/reactions}}.. Mattermost Advisory ID: MMSA-2026-00771
Overview
- State
- PUBLISHED
- Assigner (CNA)
- Mattermost
- CVSS severity
- MEDIUM
- CVSS score
- 4.3 / 10
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L- Effective score
- 4.3 / 10 MEDIUM source: CNA overview
- CWE(s)
-
CWE-770 - Reserved
- 2026-09-22
- Published
- 2026-09-22 13:11 UTC
- Last updated
- 2026-09-22 13:57 UTC
- Source
- https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/95xxx/CVE-2026-95666.json
NVD triage scoring NVD CVE 2.0
Layer NVD adds on top of the CNA's CVE record — published / last-modified timestamps, exploitability / impact subscores, and the FIRST.org EPSS probability that this CVE will be exploited in the wild in the next 30 days.
- NVD published
- 2026-09-22 14:17:21 UTC
- NVD last modified
- 2026-09-22 19:32:25 UTC
- NVD CVSS v3.1
- 4.3 / 10 MEDIUM source: responsibledisclosure@mattermost.com
- NVD CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L- Exploitability subscore
- 2.8 / 10
- Impact subscore
- 1.4 / 10
NVD / KEV / EPSS data refreshed 2026-09-23 02:30 UTC. Re-run the 🛰 Backfill from NVD button above to refresh.
European Union Vulnerability Database ENISA EUVD
ENISA's official EU repository for curated vulnerability intelligence. Carries a separate identifier (EUVD-YYYY-NNNN) and frequently exposes an earlier-published description + CVSS than NVD does.
- EUVD ID
-
EUVD-2026-84378 - Assigner
- Mattermost
- Published
- Sep 22, 2026, 1:11:13 PM
- Updated
- Sep 22, 2026, 1:57:00 PM
- EUVD base score (CVSS 3.1)
-
4.3 / 10
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L - EUVD-reported EPSS
- 0.0000
- Vendors
- Mattermost
- Products
-
Mattermost (11.10.0 ≤11.10.1)Mattermost (11.7.0 ≤11.7.10)Mattermost (11.8.0 ≤11.8.5)Mattermost (11.9.0 ≤11.9.1)
- Aliases
-
GHSA-h2qv-vjc9-5g55
ENISA description: Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to limit the length of the post ID array accepted by the bulk reactions endpoint which allows an authenticated user to cause excessive database load via a crafted request to {{POST /api/v4/posts/ids/reactions}}.. Mattermost Advisory ID: MMSA-2026-00771
EUVD references (1)
Affected products (1)
| Vendor | Product | Versions | Platforms |
|---|---|---|---|
| Mattermost | Mattermost |
11.9.0 (affected),
11.8.0 (affected),
11.7.0 (affected),
11.10.0 (affected),
11.11.0 (unaffected),
11.9.2 (unaffected),
11.8.6 (unaffected),
11.7.11 (unaffected),
11.10.2 (unaffected)
|
— |
Vendor references (1)
References embedded in the original CVE record by the assigning CNA.
- MMSA-2026-00771 vendor-advisory
Web references (0)
DuckDuckGo results ranked by threat-intel / vendor advisory domains. Generated by the 🔎 Find references (web) button above — same flow as the Remediations search.
No web references attached yet.
NVD-tagged references (1)
Reference list NVD curates from the CNA record, vendor advisories, and third-party reports. The tag chips below are NVD's analyst-assigned categories.
- https://mattermost.com/security-updates responsibledisclosure@mattermost.com
Remediations (10)
-
web:arcticwolf.com
Validate Group Policy and registry settings for Defender to ensure real-time protection, automatic remediation , and exclusion policies are secured. Temporary Workarounds Block Vulnerable Apps: Use Microsoft Defender Vulnerability Management to block or warn against execution of affected binaries for systems pending a patch .
2026-09-23 15:41 UTC -
web:cybersecuritynews.com
Microsoft has officially acknowledged a critical zero-day vulnerability in Microsoft Defender, publicly dubbed "RoguePlanet," and confirmed it is actively developing a security patch to address the flaw.
2026-09-23 15:41 UTC -
web:msrc.microsoft.com
The Microsoft Security Response Center (MSRC) investigates all reports of security vulnerabilities affecting Microsoft products and services, and provides the information here as part of the ongoing effort to help you manage security risks and help keep your systems protected.
2026-09-23 15:41 UTC -
web:msrc.microsoft.com
Security Update Guide - Microsoft Security Response Center
2026-09-23 15:41 UTC -
web:securityaffairs.com
Microsoft fixed RoguePlanet ( CVE - 2026 -50656), a Defender flaw allowing local attackers to gain higher privileges through the Malware Protection Engine. Microsoft released security updates for RoguePlanet, a vulnerability tracked as CVE - 2026 -50656 (CVSS score of 7.8) affecting the Malware Protection Engine used by Defender. The Microsoft Malware Protection Engine (mpengine.dll) powers Defender ...
2026-09-23 15:41 UTC -
web:senserva.com
Every Microsoft security patch (KB) and the CVEs it fixes, with severity, CVSS, and CISA KEV status. Cross-linked to the CVE reference.
2026-09-23 15:41 UTC -
web:support.microsoft.com
This out-of-band (OOB) update for Windows 11, version 25H2 and Windows 11, version 24H2 (KB5121768) is cumulative. It includes all improvements from previous security and non-security updates, along with an additional fix . Improvements This OOB update includes the following improvement: [System Performance] This update addresses an issue affecting a limited number of devices with an Intel ...
2026-09-23 15:41 UTC -
web:support.microsoft.com
This Hotpatch update for Windows 11, version 25H2 and 24H2 (KB5079420), improves functionality, performance, and reliability. To learn more about differences between security updates, optional non-security preview updates, out-of-band (OOB) updates, and continuous innovation, see Windows monthly updates explained. For information on Windows update terminology, see the different types of ...
2026-09-23 15:41 UTC -
web:windowsforum.com
ShieldBreak, a newly published proof of concept from the researcher known as Nightmare Eclipse, claims to bypass Microsoft's July fix for the Microsoft Defender privilege-escalation flaw CVE - 2026 -50656, better known as RoguePlanet.
2026-09-23 15:41 UTC -
web:www.bleepingcomputer.com
Microsoft has released a security patch to address a Defender zero-day vulnerability known as "RoguePlanet," disclosed after the June 2026 Patch Tuesday.
2026-09-23 15:41 UTC
AI Forensic Analysis
Only Available for Registered Users. Sign in to view.
Raw JSON
The full cvelistV5 record. Download as CVE-2026-95666.json.
{
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-95666",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-09-22T13:55:15.216071Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-09-22T13:57:00.428Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"product": "Mattermost",
"vendor": "Mattermost",
"versions": [
{
"lessThanOrEqual": "11.9.1",
"status": "affected",
"version": "11.9.0",
"versionType": "semver"
},
{
"lessThanOrEqual": "11.8.5",
"status": "affected",
"version": "11.8.0",
"versionType": "semver"
},
{
"lessThanOrEqual": "11.7.10",
"status": "affected",
"version": "11.7.0",
"versionType": "semver"
},
{
"lessThanOrEqual": "11.10.1",
"status": "affected",
"version": "11.10.0",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "11.11.0"
},
{
"status": "unaffected",
"version": "11.9.2"
},
{
"status": "unaffected",
"version": "11.8.6"
},
{
"status": "unaffected",
"version": "11.7.11"
},
{
"status": "unaffected",
"version": "11.10.2"
}
]
}
],
"credits": [
{
"lang": "en",
"type": "finder",
"value": "idr"
}
],
"descriptions": [
{
"lang": "en",
"value": "Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to limit the length of the post ID array accepted by the bulk reactions endpoint which allows an authenticated user to cause excessive database load via a crafted request to {{POST /api/v4/posts/ids/reactions}}.. Mattermost Advisory ID: MMSA-2026-00771"
}
],
"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-770",
"description": "CWE-770: Allocation of Resources Without Limits or Throttling",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-09-22T13:11:13.798Z",
"orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee",
"shortName": "Mattermost"
},
"references": [
{
"name": "MMSA-2026-00771",
"tags": [
"vendor-advisory"
],
"url": "https://mattermost.com/security-updates"
}
],
"solutions": [
{
"lang": "en",
"value": "Update Mattermost to versions 11.11.0, 11.9.2, 11.8.6, 11.7.11, 11.10.2 or higher."
}
],
"source": {
"advisory": "MMSA-2026-00771",
"defect": [
"https://mattermost.atlassian.net/browse/MM-70177"
],
"discovery": "EXTERNAL"
},
"title": "Unbounded post ID array in the bulk reactions endpoint allows denial of service",
"x_generator": {
"engine": "cvelib 1.8.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee",
"assignerShortName": "Mattermost",
"cveId": "CVE-2026-95666",
"datePublished": "2026-09-22T13:11:13.798Z",
"dateReserved": "2026-09-22T13:09:02.237Z",
"dateUpdated": "2026-09-22T13:57:00.428Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}