Elmah is an application-wide error logging facility that is completely pluggable.This vulnerability can cause highly sensitive data leaks on current sessions. It is a powerful tool that helps developers debug and resolve problems in their applications.it is configured improperly on target websites, and that allows attackers to gain information about requests and responses to the application. Information such as:
Session cookies
Session state
Query string and post variables
Physical path of the requested file
This means that the attacker can hijack any active user’s session by using their session details.
Apply the changes in web.config file to disable remote access to the Elmah.axd error log.
Also uses ASP.NET’s own authorization mechanism to protect Elmah.axd error log from attackers. It makes the Elmah.axd error log viewable by only authorized Administrators.