An undercut attack, as described in this article, is a mining strategy in which new blocks are not created in the longest known chain, but "undercut" the longest chain by creating a block that costs less for the available transactions, shorter chain charges. This behavior creates a direct incentive for another miner to create new blocks in the "undercutting" chain because they have a higher amount of transaction fees to collect.
In the thesis, the authors describe how this can lead to a situation in which a 51% attack can be successfully carried out with less than 51% of the hashing performance of the network. This is possible because the undercut orphaned blocks and the effective hashing performance of the network are reduced (the 51% attackers have the advantage that they do not have to orphan their own blocks, but the honest or underbidding miners work with a cumulatively lower hashing rate. Rate due on the possible orphanation of higher value blocks).
Are there solutions that affect undercutting behavior? Or can the behavior be mitigated by changing the protocol?