MCPToolIndex.search_tools() in PraisonAI accepts a user‑supplied string and compiles it directly as a Python regular expression without any validation, sanitization or timeout. An attacker can send a specially crafted pattern that triggers catastrophic backtracking in Python’s re engine, causing the thread to block for hundreds of seconds and resulting in a full service outage. The main consequence is a denial of service, affecting system availability.

The flaw exists in the PraisonAI platform developed by MervinPraison. Versions prior to 4.5.90 are vulnerable. The 4.5.90 release and later contain the necessary patch.

This vulnerability has a CVSS score of 6.5, indicating moderate severity. The EPSS score is below 1%, suggesting a low probability of exploitation in the wild, and it is not listed in the CISA KEV catalog. If the search_tools() function is exposed to external input—through an API or other interface—a remote attacker could send a crafted expression to trigger the denial of service. No additional exploitation requirements are stated in the description, so an attacker would need the ability to submit a custom regex.