CVE-2026-49284: Simplesamlphp/simplesamlphp SimpleSAMLphp SP Accepts A Response Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-q8r6-xj3f-wrrm",
  "modified" : "2026-07-02T20:47:21Z",
  "published" : "2026-07-02T20:47:21Z",
  "aliases" : [ "CVE-2026-49284" ],
  "summary" : "SimpleSAMLphp SP accepts a response from an unexpected IdP when unsigned `Response/InResponseTo` is combined with a signed assertion lacking `SubjectConfirmationData/InResponseTo`",
  "details" : "## Summary\n\nSimpleSAMLphp's SAML SP ACS path does not enforce the IdP selected for an SP-initiated login. If a saved SP state contains `ExpectedIssuer = IdP A`, but the ACS receives a valid response from `IdP B`, the code logs a warning and continues processing instead of rejecting the response.\n\nThat behavior becomes security-relevant when combined with the response-processing rule that accepts an unsigned `samlp:Response/@InResponseTo` outside the signed assertion whenever the signed assertion's `SubjectConfirmationData` does not carry its own `InResponseTo`. A response issued by one trusted IdP can therefore be bound to SP state created for another IdP.\n\n## Impact\n\nIn a multi-IdP deployment, a lower-trust IdP can satisfy SP state created for a different expected IdP. This can bypass an SP flow that intentionally routes the user to a specific IdP, including deployments that set `enable_unsolicited` to `false` to prevent IdP-initiated logins.\n\nThe impact is highest when the SP trusts multiple IdPs with different assurance levels, tenant boundaries, or attribute namespaces, and application authorization depends on the selected/expected IdP. In those deployments this is an authentication/authorization bypass candidate. Impact strongly depends on whether an attacker can obtain a signed IdP-initiated assertion from a lower-trust trusted IdP and whether the downstream application maps identifiers globally.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "simplesamlphp/simplesamlphp"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.5.0"
      }, {
        "fixed" : "2.5.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.5.1"
    }
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "simplesamlphp/simplesamlphp"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.4.7"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.4.6"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/simplesamlphp/simplesamlphp/security/advisories/GHSA-q8r6-xj3f-wrrm"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/simplesamlphp/simplesamlphp"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-345" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-02T20:47:21Z",
    "nvd_published_at" : null
  }
}