24 CFR §81.99

1. (a)Additional requirements. In any case or any class of cases arising under these regulations, a GSE may require such additional evidence and a bond of indemnity, with or without surety, as may in the judgment of the GSE be necessary for the protection of the interests of the GSE.
2. (b)Notice of attachment for GSE Securities in Book-entry system. The interest of a debtor in a Security Entitlement may be reached by a creditor only by legal process upon the Securities Intermediary with whom the debtor's securities account is maintained, except where a Security Entitlement is maintained in the name of a secured party, in which case the debtor's interest may be reached by legal process upon the secured party. These regulations do not purport to establish whether a Federal Reserve Bank is required to honor an order or other notice of attachment in any particular case or class of cases.