What’s Vulnerable › Vulnerabilities

CVE-2026-115911: vLLM: DoS via unbounded chat_template Jinja2 rendering exhausts the renderer thread pool

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-26 · updated 2026-10-30
• Weakness: CWE-400

Description

vLLM is an inference and serving engine for large language models. From 0.19.0 until 0.32.0, authenticated callers can supply a request chat template when no server-side --chat-template is configured, or a malicious model repository can provide a template that is compiled and rendered by tokenizer.apply_chat_template() without a wall-clock timeout, output-size limit, or iteration bound. Rendering runs in a ThreadPoolExecutor with one worker by default, so a nonterminating render can block /v1/responses and other chat-template users after the request ends, while an output-expanding render can exhaust server memory. Harmony models are not affected because they do not use this Jinja path. This issue is fixed in version 0.32.0.

Affected products

• vllm-project vllm: from 0.19.0 before 0.32.0 — fixed in 0.32.0
• vllm-project vllm: from 0.19.0, < 0.32.0

How to fix

Upgrade to a fixed version: vllm-project vllm 0.32.0. Check the vendor advisory for mitigations.

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-542m-9234-8gvf

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