SquirrelMail: DoS (disk space consumption) by random IMAP login attempts with 8-bit characters in the password

functions/imapgeneral.php in SquirrelMail before 1.4.21 does not properly handle 8-bit characters in passwords, which allows remote attackers to cause a denial of service disk consumption by making many IMAP login attempts with different usernames, leading to the creation of many preferences file...