Inefficient Regular Expression Complexity

Summary

A vulnerability in the `preprocess_string()` function of the `transformers.testing_utils` module in huggingface/transformers version through v4.49.0 allows for a Regular Expression Denial of Service (ReDoS) attack. The regular expression used to process code blocks in docstrings contains nested quantifiers, leading to exponential backtracking when processing input with a large number of newline characters. An attacker can exploit this by providing a specially crafted payload, causing high CPU usage and potential application downtime, effectively resulting in a Denial of Service (DoS) scenario.