What is it about?

Modern computers allow many apps to run at the same time, and for security, they are supposed to be fully isolated from each other. However, because these apps share the same internal hardware—like the Last Level Cache (LLC)—they can sometimes “peek” at each other through tiny timing differences. These hidden pathways are called covert channels, and they allow one program to secretly send information to another without using normal communication methods. Our work studies this problem and shows that even some existing security defenses designed to stop such leaks can themselves be bypassed. We discovered a new technique called the Buffer Saturation Attack (BSA), where a malicious program overwhelms an internal hardware buffer to force the system into revealing timing clues. This creates a secret communication link between two programs even when they are strictly isolated. To solve this, we designed a lightweight defence called ReCap, which quietly limits how many rapid requests any single program can send. This prevents attackers from overrunning the buffer while keeping the computer fast for normal users. Our study explains how the attack works, why the defence succeeds, and how both behave across different hardware settings.

Featured Image

Why is it important?

Hidden communication channels inside processors are becoming a major concern as modern systems increasingly run untrusted apps side-by-side—on laptops, servers, cloud platforms, and even mobile devices. These covert channels don’t rely on software bugs, so traditional security measures like access control or encryption cannot stop them. Our discovery is important for two reasons: ● We uncovered a previously unknown weakness in a widely-studied defence mechanism used to protect processors from timing-based attacks. This shows that even well-designed hardware defences can introduce new vulnerabilities if not carefully evaluated. ● We provide a practical fix. Our defence, ReCap, is simple to implement in hardware and avoids the performance penalties that many other solutions create. It stops the new attack without slowing down regular applications. By revealing this vulnerability and offering a low-cost defence, our work helps hardware designers, system architects, and cloud providers build safer processors. It also encourages the research community to examine security countermeasures more critically, ensuring that future systems are protected not only from known attacks but also from the unintended side effects of the defences themselves.

Perspectives

Working on this article was a meaningful experience for me. It helped me understand how even small design choices deep inside computer hardware can open doors to serious security risks. I hope this study encourages more research into building safer processors—especially as our devices become increasingly interconnected and dependent on shared resources. If this work can contribute even a little toward more secure hardware designs in the future, I’ll feel that it has served its purpose.

Ankur Srivastava
Indian Institute of Information Technology Guwahati

Read the Original

This page is a summary of: Breaking The Buffer : Covert Channel Attacks by Overrunning Buffer and Countermeasures, ACM Transactions on Design Automation of Electronic Systems, November 2025, ACM (Association for Computing Machinery),
DOI: 10.1145/3777554.
You can read the full text:

Read

Contributors

The following have contributed to this page