{"id":"GHSA-542m-9234-8gvf","summary":"vLLM: DoS via unbounded chat_template Jinja2 rendering exhausts the renderer thread pool","details":"### Summary\nvLLM renders chat templates by passing the resolved Jinja2 source to `tokenizer.apply_chat_template()`, which compiles and `.render()`s it in an `ImmutableSandboxedEnvironment`. The sandbox prevents code-execution escapes but imposes **no wall-clock timeout, no output-size cap, and no nested-loop or binop limit**. The render runs in a `ThreadPoolExecutor` whose `max_workers` defaults to **1**, and CPython worker threads cannot be interrupted. An authenticated API client (or a malicious model repo loaded with `trust_remote_code=False`) can therefore submit a single short template and permanently wedge **all** chat-style endpoints (`/v1/chat/completions`, `/v1/responses`, `/tokenize`, `/pooling`-chat, `/invocations`-chat) for every tenant until the process is restarted. A string-multiplication variant instead OOM-kills the API-server process. Because of a separately-reported (GHSA-jmjw-q4x3-hmc2) gate omission on `/v1/responses`, the remote authenticated attacker vector works in **default `vllm serve` configuration** with no operator opt-in.\n\n### Impact\nA single authenticated request of \u003c100 bytes permanently denies all chat-style inference (`/v1/chat/completions`, `/v1/responses`, `/tokenize`, `/pooling`-chat, `/invocations`-chat) to **every tenant** of the API-server replica until the operator restarts the process. The string-multiplication variant OOM-kills the process. In a multi-tenant deployment this is a cross-tenant denial-of-service from any one tenant. From the malicious-model angle, a model repo whose `tokenizer_config.json` carries the hostile template wedges every replica that loads it on the first legitimate chat request, with `trust_remote_code=False`.\n\n**Preconditions:** any non-harmony model (`model_type != gpt_oss`); `renderer_num_workers` at its default of 1; for the default-config authenticated API attacker vector, `--chat-template` must be unset (the default because most HF models ship their own).\n**Blast radius:** API-server process, per replica. Engine/worker processes unaffected by the CPU variant (event loop survives); affected by the memory variant (process OOM).\n**Persistence:** until process restart. Survives client disconnect.\n\nThis advisory was fixed in [MR50300](https://github.com/vllm-project/vllm/pull/50300).","aliases":["CVE-2026-115911"],"modified":"2026-10-28T21:30:03.953993336Z","published":"2026-10-28T21:14:52Z","database_specific":{"cwe_ids":["CWE-400","CWE-770","CWE-834"],"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2026-10-28T21:14:52Z","nvd_published_at":"2026-10-26T17:17:18Z"},"references":[{"type":"WEB","url":"https://github.com/vllm-project/vllm/security/advisories/GHSA-542m-9234-8gvf"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-115911"},{"type":"WEB","url":"https://github.com/vllm-project/vllm/pull/50300"},{"type":"WEB","url":"https://github.com/vllm-project/vllm/commit/cff08b461e086523cee8bba5bd3c66d302625134"},{"type":"PACKAGE","url":"https://github.com/vllm-project/vllm"},{"type":"WEB","url":"https://github.com/vllm-project/vllm/releases/tag/v0.32.0"}],"affected":[{"package":{"name":"vllm","ecosystem":"PyPI","purl":"pkg:pypi/vllm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.19.0"},{"fixed":"0.32.0"}]}],"versions":["0.19.0","0.19.1","0.20.0","0.20.1","0.20.2","0.21.0","0.22.0","0.22.1","0.23.0","0.24.0","0.25.0","0.25.1","0.26.0","0.27.0","0.27.1","0.28.0","0.29.0","0.30.0","0.31.0"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-542m-9234-8gvf/GHSA-542m-9234-8gvf.json"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"}]}