  A fundamental assumption in software security is that memory contents do not
change unless there is a legitimate deliberate modification. Classical fault
attacks show that this assumption does not hold if the attacker has physical
access. Rowhammer attacks showed that local code execution is already
sufficient to break this assumption. Rowhammer exploits parasitic effects in
DRAM to modify the content of a memory cell without accessing it. Instead,
other memory locations are accessed at a high frequency. All Rowhammer attacks
so far were local attacks, running either in a scripted language or native
code. In this paper, we present Nethammer. Nethammer is the first truly remote
Rowhammer attack, without a single attacker-controlled line of code on the
targeted system. Systems that use uncached memory or flush instructions while
handling network requests, e.g., for interaction with the network device, can
be attacked using Nethammer. Other systems can still be attacked if they are
protected with quality-of-service techniques like Intel CAT. We demonstrate
that the frequency of the cache misses is in all three cases high enough to
induce bit flips. We evaluated different bit flip scenarios. Depending on the
location, the bit flip compromises either the security and integrity of the
system and the data of its users, or it can leave persistent damage on the
system, i.e., persistent denial of service. We investigated Nethammer on
personal computers, servers, and mobile phones. Nethammer is a security
landslide, making the formerly local attack a remote attack.
