The Vaultjacking technique described in the PhishU research represents a fundamental shift from per-site credential harvesting to wholesale compromise of Google's security domain, where a single 6-digit PIN unlocks an entire synced vault of passwords and passkeys. Unlike traditional AiTM attacks that struggle with rate limits and origin binding, this method exploits the cloud-side device enrollment flow, allowing operators to replay the PIN on attacker-controlled infrastructure and decrypt all stored credentials without device access. This builds on earlier work such as Brazzell's 2020 Medium post on password manager autofill weaknesses and aligns with documented AiTM campaigns tracked by Mandiant in their 2023 report on phishing-as-a-service operations. Google’s reliance on a short PIN for security domain joins, rather than hardware-bound or multi-factor enrollment, creates a single point of failure that affects millions of users leveraging Chrome sync for banking, enterprise SSO, and crypto accounts. The technique's integration into the PhishU framework, including automated persistence via added passkeys, underscores how it evades existing reauthentication checks during new-device flows. Broader implications include accelerated erosion of passkey trust models, as the sync layer remains the weakest link despite WebAuthn's per-site protections. Infrastructure operators and governments monitoring credential theft should prioritize detection of anomalous security domain joins, as this vector could facilitate espionage or ransomware targeting high-value accounts within months.