XML Signature Wrapping is an attack pattern against signed XML documents, especially in SAML and SOAP systems. It works by changing the structure of an XML message so that the signature verifier still validates a trusted element, while the application reads a different element for the actual security decision. The result is a mismatch between what was signed and what is used.
This matters because signature checks can create a false sense of safety if the code does not bind the signature to the exact assertion, recipient, and context being consumed. Attackers may duplicate, move, or hide signed nodes and place malicious data where the parser will find it first. Defenses include strict reference resolution, rejecting duplicate IDs, hardened XML parsing, schema and audience checks, and library designs that connect signature validation to the precise element the application trusts.