{"id":"CVE-2026-115918","aliases":["GHSA-x567-49g5-p4cf"],"title":"vLLM: Responses API bypasses trust_request_chat_template for chat_template_kwargs","summary":"vLLM: Responses API bypasses trust_request_chat_template for chat_template_kwargs","severity":"medium","cvss":6.5,"cwe":["CWE-400","CWE-770"],"vendor":"vllm","product":"vllm","ecosystem":"pip","affected":["vllm >= 0.16.0, < 0.32.0"],"patched":["vllm 0.32.0"],"published":"2026-10-28","updated":"2026-10-28","sourceUpdated":"2026-10-28T21:15:00Z","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-x567-49g5-p4cf","references":[{"url":"https://github.com/vllm-project/vllm/security/advisories/GHSA-x567-49g5-p4cf"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-115918"},{"url":"https://github.com/vllm-project/vllm/pull/50300"},{"url":"https://github.com/vllm-project/vllm/commit/cff08b461e086523cee8bba5bd3c66d302625134"},{"url":"https://github.com/vllm-project/vllm/releases/tag/v0.32.0"},{"url":"https://github.com/advisories/GHSA-x567-49g5-p4cf"}],"tags":["ghsa","pip","cve.org"],"epss":0.00324,"epssPercentile":0.25414,"ingestedAt":"2026-10-26T17:33:33.054Z","slug":"CVE-2026-115918","body":"## Overview\n\n## Summary\n\nvLLM's `/v1/responses` endpoint accepts request-level `chat_template_kwargs`, but does not apply the `--trust-request-chat-template` gate that protects Chat Completions, render, tokenize, and pooling paths.\n\nWhen the server is run with the documented default `trust_request_chat_template=False` and no explicit `--chat-template`, a Responses request can pass:\n\n```json\n{\"chat_template_kwargs\": {\"chat_template\": \"<attacker Jinja template>\"}}\n```\n\nThat key is preserved by `ChatParams.get_apply_chat_template_kwargs()` and then bound as the `chat_template` parameter to the shared HF renderer. Prior vLLM advisories establish that request-controlled Jinja chat templates can cause CPU/memory exhaustion. This report covers the current-head Responses sibling path missed by the earlier fixes.\n\n## Technical Details\n\nThe shared OpenAI frontend has a validation helper that rejects request-supplied chat templates unless the trust flag is enabled. It explicitly checks both top-level `chat_template` and `chat_template_kwargs[\"chat_template\"]`.\n\nResponses is a separate serving path:\n\n- `vllm/entrypoints/openai/responses/protocol.py` exposes `chat_template_kwargs`.\n- `ResponsesRequest.build_chat_params()` merges request kwargs.\n- `OpenAIServingResponses._effective_chat_template_kwargs()` uses those kwargs.\n- `ChatParams.get_apply_chat_template_kwargs()` preserves a request `chat_template` key when the server chat template is `None`.\n- `vllm/renderers/hf.py` unpacks the result into `safe_apply_chat_template`.\n\nThere is no equivalent trust gate in `vllm/entrypoints/openai/responses/serving.py`.\n\n## Impact\n\nAn authenticated caller who can submit `/v1/responses` requests can supply a request-controlled Jinja chat template despite the trust flag being disabled. The expected fixed behavior is the same as Chat Completions: reject `chat_template_kwargs[\"chat_template\"]` unless the server was started with `--trust-request-chat-template`.\n\n## Suggested Fix\n\n- Add `trust_request_chat_template` to `OpenAIServingResponses`.\n- Pass `args.trust_request_chat_template` when constructing the Responses serving object.\n- Reject `request.chat_template_kwargs[\"chat_template\"]` before rendering when trust is false.\n- Keep ordinary kwargs such as `enable_thinking` working.\n- Add regression tests for default-deny and opt-in-allow behavior on `/v1/responses`.\n\n## Affected Package/Versions\n\nSource sweep found the affected shape in:\n\n- `v0.16.0`\n- `v0.18.0`\n- `v0.20.0`\n- `v0.21.0`\n- `v0.22.0`\n- `v0.22.1`\n- `v0.23.0`\n- current checkout `470229c37efaf69c86e8bc97482b0b1ff7551c65`\n- current `origin/main` `b3f0a0a0df76dda92ec4b2c9335f77e84adad911`\n\nSuggested affected range:\n\n```text\n>= 0.16.0, <= 0.23.0\n```\n\n## Appendix: Duplicate Research\n\nThis is related to, but distinct from:\n\n- `GHSA-6fvq-23cw-5628` / `CVE-2025-61620`\n- `GHSA-69j4-grxj-j64p` / `CVE-2025-62426`\n\nThose advisories establish the security impact of request-controlled Jinja templates and `chat_template_kwargs`, but they cover older Chat Completions/tokenize implementations. This report covers a current `/v1/responses` sibling path that still lacks the trust gate.\n\nLocal prior submissions this report..029 do not cover this root cause.\n\nThis advisory was fixed in [MR50300](https://github.com/vllm-project/vllm/pull/50300).\n\n## Affected packages\n\n- `vllm >= 0.16.0, < 0.32.0`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `vllm 0.32.0`","depth":"sunlit","depthScore":36,"depthScoreParts":{"impact":35.8,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}