Summary

Netsparker detected that Elmah.axd is accessible remotely, and Elmah has been used for error logging.

This vulnerability can cause highly sensitive data leaks on current sessions.

Impact
Elmah is a powerful tool that helps developers debug and resolve problems in their applications. However, it is configured improperly on target website, and that allows attackers to gain information about requests and responses to the application. An attacker can obtain 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.
Remediation
Apply the following changes in your web.config file to disable remote access to the Elmah.axd error log:
<elmah>
     <security allowRemoteAccess="no"/> 
</elmah>
You can also use ASP.NET's own authorization mechanism to protect your Elmah.axd error log from attackers. The following configuration makes your Elmah.axd error log viewable by only authorized Administrators:
<configuration>
  <location path="elmah.axd">
    <system.web>
      <authorization>
        <allow roles="Administrators"/>
        <deny users="*"/>
      </authorization>
    </system.web>
  </location>
</configuration>
Classifications
PCI v3.1-6.5.6, PCI v3.2-6.5.6, CAPEC-347, WASC-15, OWASP 2013-A5