The vulnerability stemmed from three key issues: 1) Explicit error messages revealing user existence (CWE-200) in password reset flow, 2) Exposure of email addresses in API responses, and 3) Observable differences between existing/non-existing user responses. The commit diff shows critical changes in user existence checking logic (removed exceptions for non-existent users), removal of email return values in authentication APIs, and test case modifications to prevent user enumeration through response validation. The vulnerable functions directly handled these information disclosure paths by providing distinct error states that attackers could observe.