Jane, a security analyst, while analyzing IDS logs, detected an event matching Regex /((\%3C)|)/|.

The regular expression provided in the question is designed to detect patterns that are typically found in XSS (Cross-Site Scripting) attacks. Here’s a breakdown of the regex pattern:

/((\%3C)|<) - This part of the pattern matches the encoded version of < which is %3C, or the symbol < itself. In HTML, this symbol denotes the start of a tag.

((\%69)|i|(\%49)) - This matches the encoded version of i which is %69, the lowercase i, or the encoded version of I which is %49.

((\%6D)|m|(\%4D)) - This matches the encoded version of m which is %6D, the lowercase m, or the encoded version of M which is %4D.

((\%67)|g|(\%47)) - This matches the encoded version of g which is %67, the lowercase g, or the encoded version of G which is %47.

[^\n]+ - This part of the pattern matches one or more characters that are not a newline character.

((\%3E)|>) - This matches the encoded version of > which is %3E, or the symbol > itself, denoting the end of an HTML tag.

The combination of these patterns is looking for a string that resembles an HTML img tag, which is a common vector for XSS attacks. XSS attacks involve injecting malicious scripts into webpages viewed by other users, exploiting the trust a user has for a particular site. XSS attacks can occur when a web application uses unsanitized user input in the output it generates.

References: The EC-Council’s Certified SOC Analyst (CSA) program covers the knowledge required to detect and analyze various types of cyber threats, including XSS attacks. The CSA program’s curriculum includes understanding of IDS logs and the ability to interpret and respond to potential security events indicated by such logs. For further study and verification, please refer to the official EC-Council CSA study guides and course materials.