What’s Vulnerable › Vulnerabilities

CVE-2025-62426: vLLM vulnerable to DoS via large Chat Completion or Tokenization requests with specially crafted `chat_template_kwargs`

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-11-21 · updated 2026-10-19
• Weakness: CWE-770

Description

vLLM is an inference and serving engine for large language models (LLMs). From version 0.5.5 to before 0.11.1, the /v1/chat/completions and /tokenize endpoints allow a chat_template_kwargs request parameter that is used in the code before it is properly validated against the chat template. With the right chat_template_kwargs parameters, it is possible to block processing of the API server for long periods of time, delaying all other requests. This issue has been patched in version 0.11.1.

Affected products

• vllm-project vllm: from 0.5.5 before 0.11.1; 0.11.1-rc0, 0.11.1-rc1 — fixed in 0.11.1

How to fix

Upgrade to a fixed version: vllm-project vllm 0.11.1. Check the vendor advisory for mitigations.

References

• https://github.com/vllm-project/vllm/blob/2a6dc67eb520ddb9c4138d8b35ed6fe6226997fb/vllm/entrypoints/chat_utils.py#L1602-L1610
• https://github.com/vllm-project/vllm/blob/2a6dc67eb520ddb9c4138d8b35ed6fe6226997fb/vllm/entrypoints/openai/serving_engine.py#L809-L814
• https://github.com/vllm-project/vllm/commit/3ada34f9cb4d1af763fdfa3b481862a93eb6bd2b
• https://github.com/vllm-project/vllm/pull/27205
• https://github.com/vllm-project/vllm/security/advisories/GHSA-69j4-grxj-j64p

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