Moov signedxml: Unauthenticated denial of service in exclusive XML canonicalization

Moov signedxml is a pure Go library for processing signed XML documents. Prior to 1.4.1, ExclusiveCanonicalization in exclusivecanonicalization.go copies the complete accumulated namespace map at every nested element before reference digest or signature checks. Attacker-controlled XML containing deeply nested elements with many unused namespace declarations causes quadratic allocation growth with depth and linear growth with prefixes per level, allowing a comparatively small document to consume multiple gigabytes of memory and terminate the process. The condition is reachable through ValidateReferences without a valid signature, matching certificate, or prior authentication, and it does not bypass signature verification. This issue is fixed in version 1.4.1.