CVE-2026-103646

Status: DeferredCritical (9.8)—

The Ultimate Multisite WordPress plugin before 2.17.0 does not require authentication before a logged-out checkout is linked to, and logged in as, an existing WordPress account matching the submitted email address, and its duplicate-account check normalizes that address differently from the lookup used to create the customer, so an unauthenticated attacker can log in as any existing user, including a Network Super Admin, whose email address they know.

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This bypass is not addressed by the 2.15.1 fix for CVE-2026-75957 and remains exploitable in all versions up to and including 2.16.1, the releases that fix was expected to cover. Exploitation requires a checkout form configured without a password field (auto-generated password) and a target account that has no existing customer record in the Ultimate Multisite WordPress plugin before 2.17.0.

CVSS

Version: 3.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Base score: 9.8

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days: 0.44%
Percentile among all scored CVEs: 37
Score date: 10/17/2026

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.

ExploitationT1190 Exploit Public-Facing Applicationinitial access95 %
Primary impactT1078.001 Default Accountsstealth · persistence · privilege escalation · initial access90 %
Secondary impactT1098.001 Additional Cloud Credentialspersistence · privilege escalation80 %

Vulnerabilidad en plugin WordPress accesible sin autenticación (AV:N, PR:N, UI:N) permite acceso a cuentas existentes mediante normalización diferenciada de direcciones de email. Impacto: autenticación como usuario legítimo incluso Network Super Admin.

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

Privileged Account Management Network Segmentation Multi-factor Authentication Vulnerability Scanning User Account Management Password Policies

Affected technologies (1)

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

Ultimate Multisite — Ultimate Multisite^AI

CWEs

CWE-287

References

https://wpscan.com/vulnerability/a05da0ad-5d92-406f-b182-b3ed1f8389f3/

Raw JSON (NVD)

Show

{
  "id": "CVE-2026-103646",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-103646",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-10-08T10:58:10.240709Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 9.8,
          "attackVector": "NETWORK",
          "baseSeverity": "CRITICAL",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 3.9
      }
    ]
  },
  "affected": [
    {
      "source": "contact@wpscan.com",
      "affectedData": [
        {
          "vendor": "Unknown",
          "product": "Ultimate Multisite",
          "versions": [
            {
              "status": "affected",
              "version": "0",
              "lessThan": "2.17.0",
              "versionType": "semver"
            }
          ],
          "defaultStatus": "unaffected"
        }
      ]
    }
  ],
  "published": "2026-10-08T06:16:37.957",
  "references": [
    {
      "url": "https://wpscan.com/vulnerability/a05da0ad-5d92-406f-b182-b3ed1f8389f3/",
      "source": "contact@wpscan.com"
    }
  ],
  "vulnStatus": "Deferred",
  "weaknesses": [
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      "description": [
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    {
      "lang": "en",
      "value": "The Ultimate Multisite  WordPress plugin before 2.17.0 does not require authentication before a logged-out checkout is linked to, and logged in as, an existing WordPress account matching the submitted email address, and its duplicate-account check normalizes that address differently from the lookup used to create the customer, so an unauthenticated attacker can log in as any existing user, including a Network Super Admin, whose email address they know.\nThis bypass is not addressed by the 2.15.1 fix for CVE-2026-75957 and remains exploitable in all versions up to and including 2.16.1, the releases that fix was expected to cover. Exploitation requires a checkout form configured without a password field (auto-generated password) and a target account that has no existing customer record in the Ultimate Multisite  WordPress plugin before 2.17.0."
    }
  ],
  "lastModified": "2026-10-08T20:51:18.123",
  "sourceIdentifier": "contact@wpscan.com"
}