CVE-2026-56191

Estado: AnalizadaCrítica (10)—

Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Puntuación base: 10

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.90%
Percentil entre todas las CVEs puntuadas: 58
Fecha de la puntuación: 4/10/2026

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

ExplotaciónT1190 Exploit Public-Facing Applicationinitial access85 %
Impacto principalT1078 Valid Accountsstealth · persistence · privilege escalation · initial access90 %
Impacto secundarioT1565 Data Manipulationimpact75 %

AV:N/PR:N sin interacción permite acceso remoto sin autenticación (T1190). CWE-287 y 'tampering' indican manipulación de datos (T1565) tras obtener acceso no autenticado (T1078).

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Privileged Account Management Network Segmentation Application Developer Guidance Active Directory Configuration Vulnerability Scanning User Training

Tecnologías afectadas (1)

Microsoft — Exchange Online

CWE

CWE-287

Referencias

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56191

JSON original (NVD)

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  "id": "CVE-2026-56191",
  "cveTags": [
    {
      "tags": [
        "exclusively-hosted-service"
      ],
      "sourceIdentifier": "secure@microsoft.com"
    }
  ],
  "metrics": {
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      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-56191",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-07-24T00:00:00+00:00"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "secure@microsoft.com",
        "cvssData": {
          "scope": "CHANGED",
          "version": "3.1",
          "baseScore": 10,
          "attackVector": "NETWORK",
          "baseSeverity": "CRITICAL",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 6,
        "exploitabilityScore": 3.9
      }
    ]
  },
  "affected": [
    {
      "source": "secure@microsoft.com",
      "affectedData": [
        {
          "vendor": "Microsoft",
          "product": "Microsoft Exchange Online",
          "versions": [
            {
              "status": "affected",
              "version": "-"
            }
          ]
        }
      ]
    }
  ],
  "published": "2026-07-24T01:17:36.417",
  "references": [
    {
      "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56191",
      "tags": [
        "Vendor Advisory"
      ],
      "source": "secure@microsoft.com"
    }
  ],
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "secure@microsoft.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-287"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network."
    }
  ],
  "lastModified": "2026-07-29T14:55:55.733",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:microsoft:exchange_online:-:*:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "DA6C3728-2BB2-4BA9-BB20-D784F18AD402"
            }
          ],
          "operator": "OR"
        }
      ]
    }
  ],
  "sourceIdentifier": "secure@microsoft.com"
}