{"cve":"CVE-2026-34756","nvd":{"published":"2026-04-06T16:16:36.610","modified":"2026-08-25T13:18:39.567","status":"Modified","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":6.5},"cwes":["CWE-770","CWE-1284"],"references":["https://github.com/vllm-project/vllm/commit/b111f8a61f100fdca08706f41f29ef3548de7380","https://github.com/vllm-project/vllm/pull/37952","https://github.com/vllm-project/vllm/security/advisories/GHSA-3mwp-wvh9-7528","https://access.redhat.com/errata/RHSA-2026:36005","https://access.redhat.com/errata/RHSA-2026:36006"],"products":["vllm:vllm"],"source":"nvd","synced_at":"2026-10-19T22:28:59.047572785+00:00"},"epss":{"cve":"CVE-2026-34756","score":0.00421,"percentile":0.36488,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-3mwp-wvh9-7528","url":"https://osv.dev/vulnerability/GHSA-3mwp-wvh9-7528","summary":"vLLM: Unauthenticated OOM Denial of Service via Unbounded `n` Parameter in OpenAI API Server","modified":"2026-09-10T03:50:42.430496411Z","packages":[{"ecosystem":"PyPI","name":"vllm","purl":"pkg:pypi/vllm","ranges":[">=0.1.0 <0.19.0"],"fixed":["0.19.0"]}]},{"id":"PYSEC-2026-2298","url":"https://osv.dev/vulnerability/PYSEC-2026-2298","summary":"","modified":"2026-07-13T07:15:12.502269986Z","packages":[{"ecosystem":"PyPI","name":"vllm","purl":"pkg:pypi/vllm","ranges":[">=0.1.0 <0.19.0"],"fixed":["0.19.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}