vllm-project vLLM up to 0.18.x HTTP Request allocation of resources

Summaryinfo

A vulnerability identified as problematic has been detected in vllm-project vLLM up to 0.18.x. Affected by this vulnerability is an unknown functionality of the component HTTP Request Handler. The manipulation leads to allocation of resources. This vulnerability is listed as CVE-2026-34756. The attack may be initiated remotely. There is no available exploit. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in vllm-project vLLM up to 0.18.x. It has been rated as problematic. This issue affects some unknown functionality of the component HTTP Request Handler. The manipulation with an unknown input leads to a allocation of resources vulnerability. Using CWE to declare the problem leads to CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. Impacted is availability. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-34756 since 03/30/2026. The exploitation is known to be easy. The attack may be initiated remotely. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 0.19.0 eliminates this vulnerability. Applying the patch b111f8a61f100fdca08706f41f29ef3548de7380 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Project Management Software

Vendor

• vllm-project

Name

• vLLM

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7
• 0.8
• 0.9
• 0.10
• 0.11
• 0.12
• 0.13
• 0.14
• 0.15
• 0.16
• 0.17
• 0.18

License

• open-source

Website

• Product: https://github.com/vllm-project/vllm/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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