  Federated recommendation is a prominent use case within federated learning,
yet it remains susceptible to various attacks, from user to server-side
vulnerabilities. Poisoning attacks are particularly notable among user-side
attacks, as participants upload malicious model updates to deceive the global
model, often intending to promote or demote specific targeted items. This study
investigates strategies for executing promotion attacks in federated
recommender systems.
  Current poisoning attacks on federated recommender systems often rely on
additional information, such as the local training data of genuine users or
item popularity. However, such information is challenging for the potential
attacker to obtain. Thus, there is a need to develop an attack that requires no
extra information apart from item embeddings obtained from the server. In this
paper, we introduce a novel fake user based poisoning attack named PoisonFRS to
promote the attacker-chosen targeted item in federated recommender systems
without requiring knowledge about user-item rating data, user attributes, or
the aggregation rule used by the server. Extensive experiments on multiple
real-world datasets demonstrate that PoisonFRS can effectively promote the
attacker-chosen targeted item to a large portion of genuine users and
outperform current benchmarks that rely on additional information about the
system. We further observe that the model updates from both genuine and fake
users are indistinguishable within the latent space.
