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CVE-2026-19867

Status: Undergoing AnalysisMedium (4.3)—
Severity4.3Medium · CVSS 3.1
Exploitation probability0.21 %higher than 11% of CVEs
Active exploitationNonot in the CISA catalog
Public exploitNot knownno public code found

Mattermost versions 11.10.x <= 11.10.0, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10 fail to cap the number and size of mention keys stored in a user's notification properties, and to bound the quadratic multibyte-keyword matching performed for each post, which allows an authenticated user to degrade post-processing latency and consume excessive CPU on behalf of other members of any channel they share via storing an oversized notify_props.mention_keys list on their own profile.. Mattermost Advisory ID: MMSA-2026-00773

CVSS

Base score
4.3
Version
3.1
Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days
0.21 %
Percentile among all scored CVEs
11
Score date
10/21/2026

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

ATT&CK techniques

How this vulnerability is exploited and what the attacker gains, in MITRE ATT&CK terms.

Vector AV:N/PR:L/UI:N: usuario autenticado en red que almacena un notify_props.mention_keys sin límite y degrada la latencia y la CPU de otros miembros.

Inferred by our analysis agent from the official description, CVSS vector and CWE, and checked by a supervisor. May contain errors.

ATT&CK mitigations that cover these techniques

Vulnerability ScanningThreat Intelligence ProgramPrivileged Account ManagementNetwork SegmentationFilter Network TrafficDisable or Remove Feature or Program

Affected technologies (1)

⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.

Mattermost — MattermostAI

CWEs

References

Show 1 references

Raw JSON (NVD)

Show
{
  "id": "CVE-2026-19867",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-19867",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-10-16T11:59:55.782423Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "responsibledisclosure@mattermost.com",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 4.3,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "LOW",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 1.4,
        "exploitabilityScore": 2.8
      }
    ]
  },
  "affected": [
    {
      "source": "responsibledisclosure@mattermost.com",
      "affectedData": [
        {
          "vendor": "Mattermost",
          "product": "Mattermost",
          "versions": [
            {
              "status": "affected",
              "version": "11.10.0",
              "versionType": "semver",
              "lessThanOrEqual": "11.10.0"
            },
            {
              "status": "affected",
              "version": "11.9.0",
              "versionType": "semver",
              "lessThanOrEqual": "11.9.1"
            },
            {
              "status": "affected",
              "version": "11.8.0",
              "versionType": "semver",
              "lessThanOrEqual": "11.8.5"
            },
            {
              "status": "affected",
              "version": "11.7.0",
              "versionType": "semver",
              "lessThanOrEqual": "11.7.10"
            },
            {
              "status": "unaffected",
              "version": "11.11.0"
            },
            {
              "status": "unaffected",
              "version": "11.10.1"
            },
            {
              "status": "unaffected",
              "version": "11.9.2"
            },
            {
              "status": "unaffected",
              "version": "11.8.6"
            },
            {
              "status": "unaffected",
              "version": "11.7.11"
            }
          ],
          "defaultStatus": "unaffected"
        }
      ]
    }
  ],
  "published": "2026-10-16T07:17:13.353",
  "references": [
    {
      "url": "https://mattermost.com/security-updates",
      "source": "responsibledisclosure@mattermost.com"
    }
  ],
  "vulnStatus": "Undergoing Analysis",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "responsibledisclosure@mattermost.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-770"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Mattermost versions 11.10.x <= 11.10.0, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10 fail to cap the number and size of mention keys stored in a user's notification properties, and to bound the quadratic multibyte-keyword matching performed for each post, which allows an authenticated user to degrade post-processing latency and consume excessive CPU on behalf of other members of any channel they share via storing an oversized notify_props.mention_keys list on their own profile.. Mattermost Advisory ID: MMSA-2026-00773"
    }
  ],
  "lastModified": "2026-10-16T19:23:18.623",
  "sourceIdentifier": "responsibledisclosure@mattermost.com"
}