The vulnerability centers on improper certificate chain validation leading to DoS. The X509Chain.Build() method is the primary entry point for certificate chain validation in .NET's cryptography stack. The advisory explicitly mentions infinite X509Chain recursion as the attack vector, which would manifest in this chain-building function. While no direct patch code is shown, the vulnerability description and affected component (X509Certificates package) strongly implicate this critical security boundary function as the vulnerable entry point.