Ghost Vectors: Soft-Deleted Embeddings Remain Reconstructible in HNSW Vector Databases
Retrieval-augmented generation (RAG) allows large language models to access external and private corpora for factual, domain-specific responses. Modern RAG pipelines use hierarchical navigable small world (HNSW) vector databases for efficient similarity search. When a user requests data deletion, the systems typically only mark the record as deleted, leaving the embedding on disk physically unchanged. This soft-delete operation raises compliance concerns under data-erasure and retention requirements such as GDPR Article 17 and HIPAA. Analysis on three HNSW implementations confirms that deleted vectors remain physically recoverable by accessing the raw index files at the storage layer, byp...
| Authors | Chandranil Chakraborttii, Jackeline García Alvarado, Sitora Abdulofizova et al. |
|---|---|
| Primary category | cs.CR |
| Published | 16 June 2026 |
| Last updated at source | 16 June 2026 |
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