Vulnerable bid (6)
I believe the answer is:
tender
I believe this is a double definition.
'vulnerable' is the first definition.
('tender' can be a synonym of 'vulnerable')
'bid' is the second definition.
('tender' can be a synonym of 'bid')
(Other definitions for tender that I've seen before include "Bid - not toughened" , "Dinghy towed by a yacht" , "Former railway vehicle is sensitive" , "Easy to cut or chew" , "Fragile" .)