CVE-2026-89043 in passport-saml-encrypted
Summary
by MITRE • 09/10/2026
passport-saml-encrypted through 0.1.13 contains an XML signature wrapping vulnerability where signature verification and assertion extraction use independent XPath lookups with no cross-validation. Attackers holding any validly signed SAML message can prepend a forged unsigned assertion that gets accepted as the verified identity while the genuine signature validates against the original assertion.
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Analysis
by VulDB Data Team • 09/10/2026
The vulnerability identified in passport-saml-encrypted versions through 0.1.13 represents a critical authentication bypass rooted in improper XML signature validation logic, specifically classified under CWE-749: Exposed Dangerous Method or Function and more precisely as an XML Signature Wrapping attack. This flaw arises from the architectural decision to perform independent XPath lookups for both signature verification and assertion extraction without implementing cross-validation between these two processes. In a standard SAML authentication flow, the service provider must ensure that the cryptographic signature corresponds exactly to the identity assertion being processed by the application logic. However, in this implementation, the mechanism used to locate the XML digital signature is distinct from the mechanism used to extract the user attributes or identity claims from the Security Assertion Markup Language document. This separation creates a structural gap that attackers can exploit through manipulation of the XML structure itself rather than breaking cryptographic protections.
The operational impact of this vulnerability allows an attacker who possesses any validly signed SAML message, potentially obtained from a previous legitimate authentication session or intercepted traffic, to forge a new assertion containing arbitrary identity data. By prepending a forged unsigned assertion to the original document and carefully manipulating element identifiers such as ID attributes, the attacker can cause the signature verification process to validate against the original, genuine assertion while the application logic extracts credentials from the newly inserted, unverified assertion. This effectively decouples the cryptographic proof of integrity from the actual identity data used for authentication. Consequently, an attacker can impersonate any user whose SAML response structure is known or predictable, leading to a complete compromise of the authentication mechanism without needing access to private keys or breaking encryption algorithms.
This type of attack aligns with MITRE ATT&CK technique T1652: Impersonation within cloud environments and general identity-based attacks, as it involves forging credentials to gain unauthorized access. It also relates to CWE-839: Numeric Race Condition if the vulnerability relies on timing or ordering ambiguities in XML parsing, though primarily it is a structural logic flaw akin to CWE-611: Improper Restriction of XML External Entity Reference when considering the broader context of XML processing vulnerabilities. The root cause lies in the failure to enforce that the signed content and the processed content are identical entities within the document tree. Secure implementations must ensure that the XPath expression used for signature verification targets the same node or set of nodes as those targeted by the assertion extraction logic, thereby preventing an attacker from inserting decoy elements that satisfy one check but not the other.
Mitigation strategies require immediate updates to versions newer than 0.1.13 where this issue has been addressed through stricter validation protocols. For systems unable to upgrade immediately, defensive measures include implementing strict XML schema validation before processing SAML responses and ensuring that signature verification is performed on a canonicalized form of the entire assertion or specific critical elements rather than relying on loose XPath matches. Additionally, applications should verify that the ID referenced by the Signature element corresponds exactly to the ID of the Assertion being processed. Enforcing one-to-one mapping between signatures and assertions eliminates the possibility of wrapping attacks where multiple assertions exist in a single document but only one is signed. Organizations must also audit their SAML configurations for similar XPath injection or parsing inconsistencies across other identity providers to prevent broader exploitation vectors within their authentication infrastructure.