Denial of Service Vulnerability in Chroma 1.5.9 via HNSW Index Parameters

Chroma version 1.5.9 contains a high-severity vulnerability (CVE-2026-85664) within its handling of Hierarchical Navigable Small World (HNSW) index parameters. The application fails to perform proper bounds validation on the 'max_neighbors', 'ef_construction', and 'ef_search' parameters when processing collection-create API requests. An unauthenticated attacker can exploit this flaw by sending crafted requests containing arbitrarily large integer values for these parameters. Upon processing, the server attempts to allocate excessive memory resources to support the requested index dimensions, leading to heap exhaustion and a denial-of-service condition during the subsequent index compaction phase. This vulnerability poses a significant risk to the stability of self-hosted Chroma instances, as it does not require prior authentication to trigger.

Impact

Successful exploitation results in an immediate service denial for the target Chroma instance. By repeatedly sending these malformed requests, an attacker can prevent the service from recovering, effectively rendering the vector database unavailable for legitimate application traffic. The impact is primarily local availability, affecting any dependent AI or data pipeline relying on the Chroma instance for storage and retrieval operations.

Recommendation

Prioritize the identification and patching of Chroma instances running version 1.5.9. As the vendor releases security updates or patches addressing CVE-2026-85664, apply them to all internet-facing and internal Chroma deployments immediately. Until a patch is available, implement network-level access control lists (ACLs) or API gateway request validation to filter requests targeting the collection-create endpoint, ensuring that the integer values for HNSW index parameters fall within reasonable, documented operational limits.