CVE-2026-34756: Vllm

Medium severity, CVSS 6.5. EPSS: 0.8% chance of exploitation in the next 30 days.

vLLM is an inference and serving engine for large language models (LLMs). From 0.1.0 to before 0.19.0, a Denial of Service vulnerability exists in the vLLM OpenAI-compatible API server. Due to the lack of an upper bound validation on the n parameter in the ChatCompletionRequest and CompletionRequest Pydantic models, an unauthenticated attacker can send a single HTTP request with an astronomically large n value. This completely blocks the Python asyncio event loop and causes immediate Out-Of-Memory crashes by allocating millions of request object copies in the heap before the request even reaches the scheduling queue. This vulnerability is fixed in 0.19.0.

Affected products

• Vllm Vllm: from 0.1.0, before 0.19.0 (fixed in 0.19.0)

Published 2026-04-06. Last modified 2026-08-25.