Description

A flaw was found in Picketlink's SP signature validation; a SAML response containing zero assertion elements matching the signature check can allow an attacker to forge a SAML response and auth as any principal with any roles on the protected application.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.1",
  "pubDate": "2026-08-11T09:17:12.687Z",
  "pubdate": "2026-08-11T09:17:12.687Z",
  "executiveSummary": "A critical vulnerability exists in Picketlink's Service Provider (SP) signature validation mechanism, specifically concerning the processing of SAML responses. The flaw manifests as an improper validation implementation when handling SAML responses that contain zero assertion elements matching the intended signature check. This cryptographic validation weakness allows an unauthorized remote attacker to bypass authentication controls entirely by forging arbitrary SAML responses. The primary impact of this vulnerability is complete authentication bypass, enabling the attacker to impersonate and authenticate as any principal, including administrative users, and acquire any arbitrary roles within the protected target application. The affected product is Picketlink, specifically within its SAML protocol handling and signature verification subsystems. The risk implications are severe, as successful exploitation leads to total compromise of application confidentiality, integrity, and availability through unauthorized privilege escalation and identity spoofing. Exploitation requires the attacker to craft a maliciously structured SAML response that evades signature verification constraints due to the absence of matching assertion elements during the cryptographic validation phase, without requiring prior valid authentication credentials or special user privileges within the vulnerable system.",
  "technicalDetails": "The vulnerability resides within the cryptographic signature validation logic of Picketlink's Service Provider (SP) implementation when processing Security Assertion Markup Language (SAML) responses. The root cause of the flaw is an inadequate assertion validation routine that fails to properly enforce signature constraints and assertion matching when a SAML response contains zero assertion elements that match the expected signature check criteria. Instead of rejecting the malformed or unverified SAML payload, the validation engine improperly handles the absence of matching signed assertions, resulting in a validation bypass.\nDuring a standard SAML authentication flow, the SP receives a SAML response from the Identity Provider (IdP) containing assertions that must be cryptographically verified using XML Signature standards (XMLDSIG). In the vulnerable Picketlink implementation, an attacker can construct a crafted SAML response where the cryptographic signature does not bind to or validate the specific assertions containing the malicious identity claims. Because the validation routine encounters zero matching assertion elements against the signature, it fails to invalidate the payload correctly and proceeds to trust the unverified claims asserted within the response body.\nThe step-by-step attack flow proceeds as follows: First, the attacker crafts a malicious SAML response XML document. This document includes arbitrary assertion elements specifying an arbitrary principal identity (e.g., administrator) and arbitrary roles. Second, the attacker bypasses the signature enforcement by exploiting the logic flaw where zero assertions match the signature check, preventing the validation engine from detecting the forgery. Third, the attacker submits the forged SAML response via HTTP POST to the protected application's Assertion Consumer Service (ACS) endpoint. Fourth, the Picketlink SP component processes the response, incorrectly validates or skips the necessary signature checks due to the missing matching assertion elements, and accepts the forged assertions as authentic. Finally, the application establishes a valid session for the attacker mapped to the specified forged principal and roles, granting unauthorized access.\nThe vulnerable component is the Picketlink SP signature validation and SAML parsing subsystem. The affected protocol is SAML. Network exposure includes any web application utilizing vulnerable versions of Picketlink as a SAML Service Provider accessible over the network. Authentication and privilege requirements to execute this specific attack are zero, as the attack itself is designed to forge authentication and bypass privilege boundaries ab initio. The post-exploitation impact includes full account takeover, horizontal and vertical privilege escalation, unauthorized data access, and administrative control over the protected application."
}