Breaking the Illusion: Automated Reasoning of GDPR Consent Violations

Recent privacy regulations such as the General Data Protection Regulation (GDPR) and the California Consumer Privacy Act (CCPA) have established legal requirements for obtaining user consent regarding the collection, use, and sharing of personal data. These regulations emphasize that consent must be informed, freely given, specific, and unambiguous. However, there are still many violations, which highlight a gap between legal expectations and actual implementation. Consent mechanisms embedded in functional web forms across websites play a critical role in ensuring compliance with data protection regulations such as the GDPR and CCPA, as well as in upholding user autonomy and trust. However, current research has primarily focused on cookie banners and mobile app dialogs. These forms are diverse in structure, vary in legal basis, and are often difficult to locate or evaluate, creating a significant challenge for automated consent compliance auditing. In this work, we present Cosmic, a novel automated framework for detecting consent-related privacy violations in web forms. Cosmic integrates three key innovations: (1) a large language model (LLM)-based framework to extract consent requirements from privacy policies and locate relevant forms using multimodal web agents; (2) a domain-specific language (DSL) to formally describe heterogeneous web form structures, enabling systematic analysis; and (3) machine-interpretable Datalog rules, derived in collaboration with privacy experts, to translate natural-language GDPR requirements into formal logic for automated verification. We evaluate our developed tool for auditing consent compliance in web forms, across 5,823 websites and 3,598 forms. Cosmic detects 3,384 violations on 94.1% of consent forms, covering key GDPR principles such as freely given consent, purpose disclosure, and withdrawal options. It achieves 98.6% and 99.1% TPR for consent and violation detection, respectively, demonstrating high accuracy and real-world applicability.