FAULT+PROBE: A Generic Rowhammer-based Bit Recovery Attack

Abstract: Rowhammer is a security vulnerability that allows unauthorized attackers to induce errors within DRAM cells. To prevent fault injections from escalating to successful attacks, a widely accepted mitigation is implementing fault checks on instructions and data. We challenge the validity of this assumption by examining the impact of the fault on the victim's functionality. Specifically, we illustrate that an attacker can construct a profile of the victim's memory based on the directional patterns of bit flips. This profile is then utilized to identify the most susceptible bit locations within DRAM rows. These locations are then subsequently leveraged during an online attack phase with side information observed from the change in the victim's behavior to deduce sensitive bit values. Consequently, the primary objective of this study is to utilize Rowhammer as a probe, shifting the emphasis away from the victim's memory integrity and toward statistical fault analysis (SFA) based on the victim's operational behavior. We show FAULT+PROBE may be used to circumvent the verify-after-sign fault check mechanism, which is designed to prevent the generation of erroneous signatures that leak sensitive information. It does so by injecting directional faults into key positions identified during a memory profiling stage. The attacker observes the signature generation rate and decodes the secret bit value accordingly. This circumvention is enabled by an observable channel in the victim. FAULT+PROBE is not limited to signing victims and can be used to probe secret bits on arbitrary systems where an observable channel is present that leaks the result of the fault injection attempt. To demonstrate the attack, we target the fault-protected ECDSA in wolfSSL's implementation of the TLS 1.3 handshake. We recover 256-bit session keys with an average recovery rate of 22 key bits/hour and a 100% success rate.