Researchers Identify Bit-Flip Vulnerability in Shared KV-Cache Blocks of LLM Serving Systems
Researchers discovered that shared KV-cache blocks in LLM serving systems like vLLM's Prefix Caching are vulnerable to bit-flip attacks without integrity protection. The vulnerability allows adversaries to silently corrupt outputs in ways that are difficult to detect, with damage accumulating over time as more requests use the affected cache. The findings highlight a previously unexamined security risk in widely-used LLM infrastructure that could be addressed with checksum-based protections.
A new study on arXiv identifies a security vulnerability in shared KV-cache blocks used by large language model serving systems, particularly vLLM's Prefix Caching feature. Unlike previous research on bit-flip attacks targeting model weights, this work examines how adversaries could corrupt the key-value cache blocks that multiple requests share. The researchers used software fault injection to characterize the vulnerability, finding three critical properties: silent divergence (where 13 of 16 bit positions in BF16 format produce altered but coherent outputs indistinguishable from legitimate responses), selective propagation (affecting only requests sharing the targeted prefix), and persistent accumulation (damage grows linearly without temporal decay). The authors propose a checksum-based countermeasure that detects single-bit corruption at scheduling time with negligible overhead, bounding cumulative damage to one batch regardless of cache lifetime. The research argues for implementing integrity protection in prefix blocks before real-world exploitation becomes feasible.
What's missing
The study relies on software fault injection under ideal bit-targeting conditions rather than demonstrating end-to-end exploitation via actual Rowhammer attacks on GPU DRAM. The practical feasibility of achieving the precise bit targeting required in real-world scenarios, the specific hardware configurations vulnerable to such attacks, and the likelihood of detection by system administrators remain open questions.
What different sources said
- arXiv cs.LGCenter
Bit-Flip Vulnerability of Shared KV-Cache Blocks in LLM Serving Systems
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