CVE-2026-55574: vLLM denial of service through structured_outputs regex parameter

Summary

CVE-2026-55574 affects vLLM, an inference and serving engine for LLMs, prior to 0.24.0. The structured_outputs.regex API parameter passes a user-supplied regular expression directly to the xgrammar and outlines grammar compiler backends without a compilation timeout, and the outlines validation performs no complexity analysis. A single request with an adversarial regex containing nested quantifiers can cause exponential state-space expansion, hanging an inference worker indefinitely and denying service.

Mitigation

Fixed in version 0.24.0.

Affected packages in the Exposure Registry

Matched by package name and ecosystem. Each entry shows whether the package delegates to a language model and how many tracked packages depend on it.

• vllmPyPILLM dependency since 2023-08-25 · 15 tracked dependents

Topics

• Inference infrastructure

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