db_verify succeeds, rebuilddb segfaults too.

What does rpm -qa -vv say? Alternatively --rebuilddb -vv?
Try rm /var/lib/rpm/Pubkeys, or add --nosignature --nodigest.

If that segfaults, then manual deletion of that header is what is needed.
http://

Manual deletion can be accomplished by downloading
    ftp://people.redhat.com/jbj/t38454.c

You will need the header instance number to be deleted,
the 1st number displayed with -vv output with rpm -qa,
or rpm --rebuilddb, as in:
    D:  read h#    2042 Header ...

Edit the header instance into t38454.c, compile, execute, run
--rebuilddb afterwards to rebuild the indices.