Abstract—Given the increasing impact of Rowhammer, and the dearth of adequate other hardware defenses, many in the security community have pinned their hopes on error-correcting code (ECC) memory as one of the few practical defenses against Rowhammer attacks. Specifically, the expectation is that the ECC algorithm will correct or detect any bits they manage to flip in memory in real-world settings. However, the extent to which ECC really protects against Rowhammer is an open research question, due to two key challenges. First, the details of the ECC implementations in commodity systems are not known. Second, existing Rowhammer exploitation techniques cannot yield reliable attacks in presence of ECC memory.