source: https://www.securityfocus.com/bid/5238/info

A vulnerability has been reported in the IMHO Roxen webmail module which may enable a malicious user of the webmail system to gain access to the account of another user. This issue is due to an error in configuration which may leak the REFERER for a session with the webmail system, which an attacker may use to access another webmail account. 

- Login with an valid user/passwd,
- Logout
- Goto URL : (((webmail_URL)))/(old_error,plain)/mail/error?error=1

This will cause the webserver to display a REFERER. This REFERER may be submitted to access another user's session.