vLLM vulnerable to Regular Expression Denial of Service

Summary

A recent review identified several regular expressions in the vllm codebase that are susceptible to Regular Expression Denial of Service (ReDoS) attacks. These patterns, if fed with crafted or malicious input, may cause severe performance degradation due to catastrophic backtracking.

1. vllm/lora/utils.py Line 173

https://github.com/vllm-project/vllm/blob/2858830c39da0ae153bc1328dbba7680f5fbebe1/vllm/lora/utils.py#L173 Risk Description:

• The regex r"\((.*?)\)\$?$" matches content inside parentheses. If input such as ((((a|)+)+)+) is passed in, it can cause catastrophic backtracking, leading to a ReDoS vulnerability.
• Using .*? (non-greedy match) inside group parentheses can be highly sensitive to input length and nesting complexity.

Remediation Suggestions:

• Limit the input string length.
• Use a non-recursive matching approach, or write a regex with stricter content constraints.
• Consider using possessive quantifiers or atomic groups (not supported in Python yet), or split and process before regex matching.

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2. vllm/entrypoints/openai/tool_parsers/phi4mini_tool_parser.py Line 52

https://github.com/vllm-project/vllm/blob/2858830c39da0ae153bc1328dbba7680f5fbebe1/vllm/entrypoints/openai/tool_parsers/phi4mini_tool_parser.py#L52

Risk Description:

• The regex r'functools\[(.*?)\]' uses .*? to match content inside brackets, together with re.DOTALL. If the input contains a large number of nested or crafted brackets, it can cause backtracking and ReDoS.

Remediation Suggestions:

• Limit the length of model_output.
• Use a stricter, non-greedy pattern (avoid matching across extraneous nesting).