{"id":"GHSA-hf3c-wxg2-49q9","aliases":[],"url":"https://o3.security/vulnerability/GHSA-hf3c-wxg2-49q9","summary":"vLLM vulnerable to Denial of Service by abusing xgrammar cache","details":"### Impact\n\nThis report is to highlight a vulnerability in XGrammar, a library used by the structured output feature in vLLM. The XGrammar advisory is here: https://github.com/mlc-ai/xgrammar/security/advisories/GHSA-389x-67px-mjg3\n\nThe [xgrammar](https://xgrammar.mlc.ai/docs/) library is the default backend used by vLLM to support structured output (a.k.a. guided decoding). Xgrammar provides a required, built-in cache for its compiled grammars stored in RAM. xgrammar is available by default through the OpenAI compatible API server with both the V0 and V1 engines.\n\nA malicious user can send a stream of very short decoding requests with unique schemas, resulting in an addition to the cache for each request. This can result in a Denial of Service by consuming all of the system's RAM.\n\nNote that even if vLLM was configured to use a different backend by default, it is still possible to choose xgrammar on a per-request basis using the `guided_decoding_backend` key of the `extra_body` field of the request with the V0 engine. This per-request choice is not available when using the V1 engine. \n### Patches\n\n* https://github.com/vllm-project/vllm/pull/16283\n\n### Workarounds\n\nThere is no way to workaround this issue in existing versions of vLLM other than preventing untrusted access to the OpenAI compatible API server.\n\n### References\n\n* https://github.com/mlc-ai/xgrammar/security/advisories/GHSA-389x-67px-mjg3","published":"2025-04-15T21:21:04Z","modified":"2025-04-15T21:21:04Z","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":"0.8.4"}],"fix":{"url":"https://github.com/vllm-project/vllm/pull/16283","label":"vllm-project/vllm#16283"},"references":[{"type":"WEB","url":"https://github.com/mlc-ai/xgrammar/security/advisories/GHSA-389x-67px-mjg3"},{"type":"WEB","url":"https://github.com/vllm-project/vllm/security/advisories/GHSA-hf3c-wxg2-49q9"},{"type":"WEB","url":"https://github.com/vllm-project/vllm/pull/16283"},{"type":"WEB","url":"https://github.com/vllm-project/vllm/commit/cb84e45ac75b42ba6795145923e8eb323bb825ad"},{"type":"PACKAGE","url":"https://github.com/vllm-project/vllm"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2025-04-15T21:21:04Z"}}