{"id":"CVE-2026-34756","aliases":["GHSA-3mwp-wvh9-7528","PYSEC-2026-2298"],"url":"https://o3.security/vulnerability/CVE-2026-34756","summary":"vLLM Affected by Unauthenticated OOM Denial of Service via Unbounded `n` Parameter in OpenAI API Server","details":"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":"2026-08-07T11:50:58.316653865Z","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"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"vllm","fixedVersion":"0.19.0"}],"fix":{"url":"https://github.com/vllm-project/vllm/commit/b111f8a61f100fdca08706f41f29ef3548de7380","label":"vllm-project/vllm@b111f8a"},"references":[{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34756.json"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:36005"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:36006"},{"type":"ADVISORY","url":"https://access.redhat.com/security/cve/CVE-2026-34756"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34756.json"},{"type":"ADVISORY","url":"https://github.com/vllm-project/vllm/security/advisories/GHSA-3mwp-wvh9-7528"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-34756"},{"type":"REPORT","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2455425"},{"type":"FIX","url":"https://github.com/vllm-project/vllm/commit/b111f8a61f100fdca08706f41f29ef3548de7380"},{"type":"FIX","url":"https://github.com/vllm-project/vllm/pull/37952"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T11:50:58.316653865Z"}}