backuppc: cross-site scripting

From the Ubuntu advisory:

It was discovered that BackupPC did not properly sanitize its input when processing RestoreFile error messages, resulting in a cross-site scripting (XSS) vulnerability. With cross-site scripting vulnerabilities, if a user were tricked into viewing server output during a crafted server request, a remote attacker could exploit this to modify the contents, or steal confidential data, within the same domain.