vLLM is an inference and serving engine for large language models.
CVE-2026-115918
Summary vLLM's /v1/responses endpoint accepts request-level chattemplatekwargs, but does not apply the --trust-request-chat-template gate that protects Chat Completions, render, tokenize, and pooling paths. When the server is run with the documented default trustrequestchattemplate=False and no explicit --chat-template, a Responses request can pass: json {"chattemplatekwargs": {"chattemplate": " "}} That key is preserved by ChatParams.getapplychattemplatekwargs() and then bound as the chattemplate 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. Technical Details The 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 chattemplate and chattemplatekwargs["chattemplate"]. Responses is a separate serving path: vllm/entrypoints/openai/responses/protocol.py exposes chattemplatekwargs. ResponsesRequest.buildchatparams() merges request kwargs. OpenAIServingResponses.effectivechattemplatekwargs()…
Part of the AI stack
This affects vLLM, in Inference & serving.
Assessment
- CVSS
- 6.5 (v3.1)
- Severity
- Medium
- EPSS
- 0.0035% chance of exploitation in the next 30 days
- Known exploited
- Not listed in CISA KEV
- Exploit availability
- Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
- Published
- 26 October 2026
- Last updated
- 30 October 2026
- Affected
- pip · vllm
- Weakness
- CWE-400, CWE-770
- Assigner
- security-advisories@github.com
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
At the source
References
- https://github.com/vllm-project/vllm/commit/cff08b461e086523cee8bba5bd3c66d302625134
- https://github.com/vllm-project/vllm/pull/50300
- https://github.com/vllm-project/vllm/releases/tag/v0.32.0
- https://github.com/vllm-project/vllm/security/advisories/GHSA-x567-49g5-p4cf
- https://nvd.nist.gov/vuln/detail/CVE-2026-115918
- https://github.com/advisories/GHSA-x567-49g5-p4cf
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