vLLM AIBrix xxhash64 seed collision vulnerability (CVE-2025-1953)
AIBrix's prefix caching mechanism used xxhash64 with a predictable fixed seed value, allowing attackers to craft malicious prompts that collide with target hashes and cause cache pollution. The vulnerability was fixed by implementing random seed generation for xxhash on gateway initialization.
What happened
AIBrix's prefix caching mechanism relied on the xxhash64 hash algorithm with a fixed seed value (seed=0) in its default configuration, making hash outputs predictable.
Attackers could exploit this determinism to craft specific inputs that generate hash collisions with target prompts, causing cache pollution and subsequent response errors.
Reported impact
Maliciously crafted prompts could cause hash collisions, leading to prefix cache reuse that would interfere with subsequent responses and result in unintended behavior.
Governance controls
The issue was fixed by implementing random seed generation for xxhash on every gateway initialization, preventing attackers from predicting or forcing collisions.
The fix was merged on February 27, 2025, and enables global cache sharing across the cluster while maintaining security.
Classification
Sources and evidence
This record was researched and written by the Index, based on the following original reporting.