What’s Vulnerable › Vulnerabilities

CVE-2026-73559: vLLM: Completion prompt lists fan out into unbounded engine requests

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-08-13 · updated 2026-09-28
• Weakness: CWE-400

Description

vLLM is an inference and serving engine for large language models. From 0.19.0 until 0.26.0, the /v1/completions CompletionRequest.prompt field in vllm/entrypoints/openai/completion/protocol.py accepts an unbounded list[str] or list[list[int]], prompt_to_seq() in vllm/renderers/inputs/preprocess.py and OnlineRenderer.preprocess_completion() in vllm/renderers/online_renderer.py expand every element, and vllm/entrypoints/openai/completion/serving.py creates one engine generator and response slot per prompt, allowing an authenticated API client to exhaust CPU, memory, async scheduling capacity, engine request slots, and response buffering with one request. This issue is fixed in version 0.26.0.

Affected products

• vllm-project vllm: from 0.19.0 before 0.26.0 — fixed in 0.26.0

How to fix

Upgrade to a fixed version: vllm-project vllm 0.26.0. Check the vendor advisory for mitigations.

References

• https://github.com/vllm-project/vllm/commit/675f4295cdfe0d870471c2b51bfeca3a68a9569e
• https://github.com/vllm-project/vllm/pull/47845
• https://github.com/vllm-project/vllm/releases/tag/v0.26.0
• https://github.com/vllm-project/vllm/security/advisories/GHSA-87x5-vmc3-756j
• https://github.com/vllm-project/vllm/security/advisories/GHSA-87x5-vmc3-756j

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