The Investigative Committee said the 39-year-old woman was injured by an improvised explosive device in a forest in the central Russian city of Kursk.
She had gone to the forest to collect a package that an anonymous note said would contain the documents needed to settle her father's financial problems.
As the woman picked up the package, the explosive device went off.
Police detained her ex-husband, who confessed to manufacturing and planting the explosive device and luring the woman to the spot where he had hidden it.
The man said his plan was to get his former spouse, who had divorced him in October 2010, to return to him "by having her believe that he is her sole protector", the committee said in a statement.
The woman lost a finger and part of another in the blast, which also broke several of her wrist bones and other fingers.
A criminal case has been opened on attempted murder charges.