vLLM Affected by Unauthenticated OOM Denial of Service via Unbounded `n` Parameter in OpenAI API Server_CVE-2026-34756

{
    "lastseen": "",
    "description": "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.",
    "published": "2026-04-06T15:40:03.448Z",
    "modified": "2026-04-07T14:17:12.597Z",
    "type": "cve",
    "title": "vLLM Affected by Unauthenticated OOM Denial of Service via Unbounded `n` Parameter in OpenAI API Server",
    "source": "GitHub_M",
    "references": "https://github.com/vllm-project/vllm/security/advisories/GHSA-3mwp-wvh9-7528\nhttps://github.com/vllm-project/vllm/pull/37952\nhttps://github.com/vllm-project/vllm/commit/b111f8a61f100fdca08706f41f29ef3548de7380",
    "id": "CVE-2026-34756",
    "bulletinFamily": "",
    "cwe": [
        "CWE-770"
    ],
    "cvelist": null,
    "sourceData": "vllm-project vllm >= 0.1.0, < 0.19.0",
    "sourceHref": "",
    "cvss": {
        "score": 6.5,
        "severity": "MEDIUM",
        "vector": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
        "version": "3.1"
    },
    "cvss2": [],
    "cvss3": {
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        "baseScore": 0,
        "baseSeverity": "",
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        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
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            "baseScore": 0,
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        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "vllm",
    "version": ">= 0.1.0, < 0.19.0",
    "vendor": "vllm-project",
    "ai_description": "",
    "ai_severity": "",
    "ai_vendor": "",
    "ai_product": "",
    "ai_version": "",
    "ai_score": 0
}