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Response snapshot Oct 29, 2026, 01:26 UTC

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VulnerabilityCVE-2026-115918

vLLM: Responses API bypasses trust_request_chat_template for chat_template_kwargs

vLLM'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.

At a glance

Exploited
Not known
Severity
6.5 Medium (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: vllm: 0.32.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-x567-49g5-p4cf (opens a new tab)

What happened

Summary

vLLM'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.

When the server is run with the documented default trust_request_chat_template=False and no explicit --chat-template, a Responses request can pass:

{"chat_template_kwargs": {"chat_template": " "}}
Continue reading

That 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.

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 chat_template and chat_template_kwargs["chat_template"].

Responses is a separate serving path:

- vllm/entrypoints/openai/responses/protocol.py exposes chat_template_kwargs. - ResponsesRequest.build_chat_params() merges request kwargs. - OpenAIServingResponses._effective_chat_template_kwargs() uses those kwargs. - ChatParams.get_apply_chat_template_kwargs() preserves a request chat_template key when the server chat template is None. - vllm/renderers/hf.py unpacks the result into safe_apply_chat_template.

There is no equivalent trust gate in vllm/entrypoints/openai/responses/serving.py.

Impact

An 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.

Suggested Fix

- Add trust_request_chat_template to OpenAIServingResponses. - Pass args.trust_request_chat_template when constructing the Responses serving object. - Reject request.chat_template_kwargs["chat_template"] before rendering when trust is false. - Keep ordinary kwargs such as enable_thinking working. - Add regression tests for default-deny and opt-in-allow behavior on /v1/responses.

Affected Package/Versions

Source sweep found the affected shape in:

- v0.16.0 - v0.18.0 - v0.20.0 - v0.21.0 - v0.22.0 - v0.22.1 - v0.23.0 - current checkout 470229c37efaf69c86e8bc97482b0b1ff7551c65 - current origin/main b3f0a0a0df76dda92ec4b2c9335f77e84adad911

Suggested affected range:

>= 0.16.0, <= 0.23.0

Appendix: Duplicate Research

This is related to, but distinct from:

- GHSA-6fvq-23cw-5628 / CVE-2025-61620 - GHSA-69j4-grxj-j64p / CVE-2025-62426

Those 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.

Local prior submissions this report..029 do not cover this root cause.

This advisory was fixed in [MR50300](https://github.com/vllm-project/vllm/pull/50300).

Affected package ranges reported by GitHub: vllm: >= 0.16.0, < 0.32.0

Scores and how they were measured

CVSS base severity

6.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-x567-49g5-p4cf (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-x567-49g5-p4cf, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 28). vLLM: Responses API bypasses trust_request_chat_template for chat_template_kwargs (CVE-2026-115918). https://kevwire.com/record/CVE-2026-115918

MLA

"vLLM: Responses API bypasses trust_request_chat_template for chat_template_kwargs (CVE-2026-115918)." KEVWire, 28 Oct. 2026, kevwire.com/record/CVE-2026-115918.

Chicago

KEVWire. "vLLM: Responses API bypasses trust_request_chat_template for chat_template_kwargs (CVE-2026-115918)." Last modified October 28, 2026. https://kevwire.com/record/CVE-2026-115918.

Evidence summary (plain text)

vLLM: Responses API bypasses trust_request_chat_template for chat_template_kwargs (Oct 28, 2026).
vLLM'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.

When the server is run with the documented default trust_request_chat_template=False and no explicit --chat-template, a Responses request can pass:

That key is preserved by ChatParams.get_apply_chat_template_kwargs() and then bound as the chat_template parameter to the shared HF renderer.
CVSS 6.5 (version 3.1; evidence as of Oct 28, 2026; https://github.com/advisories/GHSA-x567-49g5-p4cf).
Sources:
GitHub-reviewed advisory GHSA-x567-49g5-p4cf: https://github.com/advisories/GHSA-x567-49g5-p4cf
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-115918.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 29, 2026, 00:55 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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