The vulnerability lies in the improper sanitization of LDFLAGS directives used with cgo. The provided patch commit 356a419e2f811b65d227abcea1a346f8dcb154e0 modifies the regular expressions in validLinkerFlags within src/cmd/go/internal/work/security.go. These regexes are used by the checkLinkerFlags function in the same file to validate linker flags. The changes make the validation stricter, specifically for flags like -Wl,-O, -Wl,-e, and -Wl,-R, ensuring they are followed by mandatory arguments. This directly addresses the vulnerability described, where non-optional arguments were treated as optional, allowing flag smuggling. Therefore, cmd/go/internal/work.checkLinkerFlags is the function that, prior to the patch, would process and incorrectly sanitize the malicious input, making it the key vulnerable function in the runtime profile during exploitation.