TF2 Item Format helps users format TF2 items to the community standards. Versions of tf2-item-format since at least 4.2.6 and prior to 5.9.14 are vulnerable to a Regular Expression Denial of Service (ReDoS) attack when parsing crafted user input. This vulnerability can be exploited by an attacker to perform DoS attacks on any service that uses any tf2-item-format to parse user input. Version 5.9.14 contains a fix for the issue.
The product uses a regular expression that either (1) contains an executable component with user-controlled inputs, or (2) allows a user to enable execution by inserting pattern modifiers.