Change groups before changing uid. Once you've dropped root permissions you're dropping the permission to modify your groups.
$GID = $new_gid;
$EGID = "$new_gid $new_gid";
$UID = $new_uid;
$EUID = $new_uid;

[download]
should work.

In reply to Re: changing uid/gid in suid cgi script by Anonymous Monk
in thread changing uid/gid in suid cgi script by bless$self=>perlmonks;

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