Yuhang Chen, Zhen Tan, Ajay Kumar Jaiswal, Huaizhi Qu, Xinyu Zhao, Qi Lin, Yu Cheng, Andrew Kwong, Zhichao Cao, Tianlong Chen. Proceedings of the 2025 Conference on Empirical Methods in Natural Language Processing. 2025.

As post-quantum cryptography (PQC) nears standardization and eventual deployment, it is increasingly important to understand the security of the implementations of selected schemes. In this paper, we conduct such an investigation, uncovering concerning findings about many of the finalists of the NIST PQC standardization competition. Specifically, we show Rowhammer-based attacks on the Kyber and BIKE Key Exchange Mechanisms and the Dilithium Digital Signature scheme that enable complete recovery of the secret key with only a moderate amount of effort - no supercomputers, or months of precomputation. Moreover, we experimentally carry out our attacks using a combination of Rowhammer, performance degradation, and memory massaging techniques, showing that our attacks are practically feasible. Our results show that such side-channel based attacks are a critical concern and need to be considered when new cryptographic schemes are standardized, when standard implementations are developed, and when instances are deployed. We conclude with recommendations on implementation techniques that harden cryptographic schemes against Rowhammer attacks.

This paper introduces novel attack primitives that enable adversaries to leak (read) and manipulate (write) the path history register (PHR) and the prediction history tables (PHTs) of the conditional branch predictor in high-performance CPUs. These primitives enable two new classes of attacks: first, it can recover the entire control flow history of a victim program by exploiting read primitives, as demonstrated by a practical secret-image recovery based on capturing the entire control flow of libjpeg routines. Second, it can launch extremely high-resolution transient attacks by exploiting write primitives. We demonstrate this with a key recovery attack against AES based on extracting intermediate values.

In this work, we recover the private key material of the FrodoKEM key exchange mechanism as submitted to the NIST Post Quantum Cryptography (PQC) standardization process.

The recent Spectre attacks have revealed how the performance gains from branch prediction come at the cost of weakened security. Spectre Variant 1 (v1) shows how an attacker-controlled variable passed to speculatively executed lines of code can leak secret information to an attacker. Numerous defenses have since been proposed to prevent Spectre attacks, each attempting to block all or some of the Spectre variants. In particular, defenses using taint-tracking are claimed to be the only way to protect against all forms of Spectre v1. However, we show that the defenses proposed thus far can be bypassed by combining Spectre with the well-known Rowhammer vulnerability. By using Rowhammer to modify victim values, we relax the requirement that the attacker needs to share a variable with the victim. Thus, defenses that rely on this requirement, such as taint-tracking, are no longer effective. Furthermore, without this crucial requirement, the number of gadgets that can potentially be used to launch a Spectre attack increases dramatically; those present in Linux kernel version 5.6 increases from about 100 to about 20,000 via Rowhammer bit-flips. Attackers can use these gadgets to steal sensitive information such as stack cookies or canaries, or use new triple gadgets to read any address in memory. We demonstrate two versions of the combined attack on example victims in both user and kernel spaces, showing the attack’s ability to leak sensitive data.

Recent transient-execution attacks, such as RIDL, Fallout, and ZombieLoad, demonstrated that attackers can leak information while it transits through microarchitectural buffers. Named Microarchitectural Data Sampling (MDS) by Intel, these attacks are likened to "drinking from the firehose", as the attacker has little control over what data is observed and from what origin. Unable to prevent the buffers from leaking, Intel issued countermeasures via microcode updates that overwrite the buffers when the CPU changes security domains.In this work we present CacheOut, a new microarchitectural attack that is capable of bypassing Intel’s buffer overwrite countermeasures. We observe that as data is being evicted from the CPU’s L1 cache, it is often transferred back to the leaky CPU buffers where it can be recovered by the attacker. CacheOut improves over previous MDS attacks by allowing the attacker to choose which data to leak from the CPU’s L1 cache, as well as which part of a cache line to leak. We demonstrate that CacheOut can leak information across multiple security boundaries, including those between processes, virtual machines, user and kernel space, and from SGX enclaves.

Modern cryptography requires the ability to securely generate pseudorandom numbers. However, despite decades of work on side-channel attacks, there is little discussion of their application to pseudorandom number generators (PRGs). In this work we set out to address this gap, empirically evaluating the side-channel resistance of common PRG implementations.We find that hard-learned lessons about side-channel leakage from encryption primitives have not been applied to PRGs, at all abstraction levels. At the design level, the NIST-recommended CTR_DRBG does not have forward security if an attacker is able to compromise the state (e.g., via a side-channel). At the primitive level, popular implementations of CTR_DRBG such as OpenSSL's FIPS module and NetBSD's kernel use leaky T-table AES as their underlying cipher, enabling cache side-channel attacks. Finally, we find that many implementations make parameter choices that enable an attacker to fully exploit side-channels and recover secret keys from TLS connections.We empirically demonstrate our attack in two scenarios. First, we carry out a cache attack that recovers the private state from vulnerable CTR_DRBG implementations when the TLS client connects to an attacker-controlled server. We then subsequently use the recovered state to compute the client's long-term authentication keys, thereby allowing the attacker to impersonate the client. In the second scenario, we show that an attacker can exploit the high temporal resolution provided by Intel SGX to carry out a blind attack to recover CTR_DRBG's state within three AES encryptions, without viewing output, and thus decrypt passively collected TLS connections from the victim.

The Rowhammer bug is a reliability issue in DRAM cells that can enable an unprivileged adversary to flip the values of bits in neighboring rows on the memory module. Previous work has exploited this for various types of fault attacks across security boundaries, where the attacker flips inaccessible bits, often resulting in privilege escalation. It is widely assumed however, that bit flips within the adversary's own private memory have no security implications, as the attacker can already modify its private memory via regular write operations.We demonstrate that this assumption is incorrect, by employing Rowhammer as a read side channel. More specifically, we show how an unprivileged attacker can exploit the data dependence between Rowhammer induced bit flips and the bits in nearby rows to deduce these bits, including values belonging to other processes and the kernel. Thus, the primary contribution of this work is to show that Rowhammer is a threat to not only integrity, but to confidentiality as well.Furthermore, in contrast to Rowhammer write side channels, which require persistent bit flips, our read channel succeeds even when ECC memory detects and corrects every bit flip. Thus, we demonstrate the first security implication of successfully-corrected bit flips, which were previously considered benign.To demonstrate the implications of this read side channel, we present an end-to-end attack on OpenSSH 7.9 that extracts an RSA-2048 key from the root level SSH daemon. To accomplish this, we develop novel techniques for massaging memory from user space into an exploitable state, and use the DRAM rowbuffer timing side channel to locate physically contiguous memory necessary for double-sided Rowhammering. Unlike previous Rowhammer attacks, our attack does not require the use of huge pages, and it works on Ubuntu Linux under its default configuration settings.

Security conscious individuals may take considerable measures to disable sensors in order to protect their privacy. However, they often overlook the cyberphysical attack surface exposed by devices that were never designed to be sensors in the first place. Our research demonstrates that the mechanical components in magnetic hard disk drives behave as microphones with sufficient precision to extract and parse human speech. These unintentional microphones sense speech with high enough fidelity for the Shazam service to recognize a song recorded through the hard drive. This proof of concept attack sheds light on the possibility of invasion of privacy even in absence of traditional sensors. We also present defense mechanisms, such as the use of ultrasonic aliasing, that can mitigate acoustic eavesdropping by synthesized microphones in hard disk drives.

Intentional acoustic interference causes unusual errors in the mechanics of magnetic hard disk drives in desktop and laptop computers, leading to damage to integrity and availability in both hardware and software such as file system corruption and operating system reboots. An adversary without any special purpose equipment can co-opt built-in speakers or nearby emitters to cause persistent errors. Our work traces the deeper causality of these risks from the physics of materials to the I/O request stack in operating systems for audible and ultrasonic sound. Our experiments show that audible sound causes the head stack assembly to vibrate outside of operational bounds; ultrasonic sound causes false positives in the shock sensor, which is designed to prevent a head crash. The problem poses a challenge for legacy magnetic disks that remain stubbornly common in safety critical applications such as medical devices and other highly utilized systems difficult to sunset. Thus, we created and modeled a new feedback controller that could be deployed as a firmware update to attenuate the intentional acoustic interference. Our sensor fusion method prevents unnecessary head parking by detecting ultrasonic triggering of the shock sensor.