You can fix the query string by stripping the f's, then re-interpret it:
<sandr "%ffffff=\xdigit{2}" "%\2" $QUERY_STRING>
<readvars "" $ret>
The <sandr> removes the ffffff's, and <readvars> re-reads all the variables listed in the query string from the new value.
<sandr "%ffffff=\xdigit{2}" "%\2" $QUERY_STRING>
<readvars "" $ret>
The <sandr> removes the ffffff's, and <readvars> re-reads all the variables listed in the query string from the new value.