Researchers from three universities in Hong Kong have published a paper demonstrating a method of eavesdropping through fiber-optic cables. Fiber optics have long been the gold standard for data transmission due to their ability to transfer information at high speeds over long distances. Fiber-optic cabling utilizes ultra-thin glass threads for transmission, and is widely used not only for backbone data lines but also for connecting individual premises. And as it turns out, these very glass threads are sensitive enough to vibrations that they subtly alter the parameters of the optical signal.

Potentially, this allows a fiber-optic cable to be turned into a microphone and intercept room conversations while being kilometers away from the sound source. In other words, this exploits so-called side channels — non-obvious characteristics of everyday home or office appliances that enable information leaks. Of course, this work is largely theoretical, much like other similar studies we’ve covered previously — eavesdropping through mouse sensors, using RAM modules as radio transmitters, exfiltrating data from CCTV sensors, or screen snooping through HDMI cables. However, several news outlets have reported on the Hong Kong researchers’ study as if it were a turnkey method, so let’s try to determine just how dangerous it really is in practice.

Hurdles of optical eavesdropping

The unique characteristics of fiber-optic cables were first considered back in 2012 by Russian researchers, who conceded the theoretical possibility of such an attack. The goal of the Hong Kong researchers was to demonstrate at least some level of practical implementation for eavesdropping.

Diagram of a provider’s fiber-optic network showing the location of the attacker and the room targeted for eavesdropping. Source

The diagram above illustrates a typical FTTH (fiber-to-the-home) network architecture, where end users or organizations connect directly to a fiber-optic cable. The ISP manages the so-called Optical Distribution Network (ODN), to which end-users are connected. The device on the user’s end is called an Optical Networking Unit (ONU).

An attack leveraging this equipment is quite difficult to execute. To eavesdrop on a specific ONU endpoint, a potential adversary would need access to the provider’s infrastructure and control over the ODN equipment. What exactly is this device? It’s a network router or an optical-to-Ethernet converter — a small box usually tucked away in an office utility closet. Inside the premises, connectivity is provided either by Wi-Fi or a local network using Ethernet cabling. Crucially, the fiber-optic cable is unlikely to run directly into a sensitive area like a CEO’s office — the very place where eavesdropping would be most relevant.

Schematic representation of the eavesdropping setup on the attacker’s side. Source

And here’s a rough idea of what the attacker’s equipment would look like. Using special tech, they send optical pulses down the fiber-optic cable and measure the parameters of their transmission. Minor vibrations from footsteps in a room near the cable and nearby conversations trigger an effect known as Rayleigh scattering. This effect, in turn, causes minute deviations in the reflected signal’s parameters, which are then captured on the attacker’s end using a photosensor.

Recording the sound of footsteps in a room through a fiber-optic cable. Source

Before moving on to voice recording, the researchers decided to test a simpler scenario. To streamline the task, they ran the fiber-optic cable around the perimeter of the room and recorded footsteps — which generate significant vibration — rather than quiet conversation. This experiment was quite successful — the footsteps were audible. However, human speech proved to be far more challenging to capture. It turned out that even in laboratory conditions, intercepting a conversation between two people was impossible. To make further stages of the attack possible, the researchers assumed the presence of a bug at the fiber’s entry point into the room. This module is essentially a microphone that converts audio signals into vibrations on the optical cable. This amplifies the signal, making it possible to intercept on the attacker’s side.

Not-so-obvious advantages

But wait — if we’re talking about planting a bug in a room, why go through all the trouble with fiber optics? Why not just have the bug transmit the conversation on its own through cellular data or the building’s landline — especially since it’s already sitting right on top of it? Because there’s a distinct advantage to the researchers’ proposed attack scenario.

A regular bug transmitting audio over a cellular network or through the internet is fairly easy to detect, whereas a transmitter relaying data via fiber-optic cable vibrations can operate much more stealthily. Such a tap would be relatively easy to implant during the installation of network equipment, and harder to detect using traditional bug-sweeping tools.

Another major benefit of this hypothetical attack is that the eavesdropping can take place kilometers away from the target room — the attacker wouldn’t have to put themselves at extra risk by being near the target. Theoretically, one could also imagine a scenario where a separate fiber-optic cable is run into a room solely for surveillance purposes without raising much suspicion from those being surveilled.

Practical takeaways

If we frame the question as, “Can attackers remotely eavesdrop on any room that has fiber-optic cabling?” the answer is no; it’s still impossible. However, this work by the Hong Kong researchers, which highlights quirks of a common data transmission medium, demonstrates a technically feasible — albeit unlikely and quite expensive to execute — scenario for a targeted attack.

It’s one of those coincidences: independent university research teams stumble onto something new and prep their papers for publication — only to realize they’ve solved the exact same puzzle using slightly different methods. That’s exactly what happened with GDDRHammer and GeForge. These two studies describe Rowhammer-style attacks that are so similar the researchers decided to publish them as a joint effort. Then, while we were putting this post together, a third study surfaced — GPUBreach — detailing yet another comparable attack. So today we’re looking at all three.

All three theoretical attacks target graphics accelerators, though this term is not entirely accurate anymore since these devices are so good at parallel processing, they’ve moved far beyond just rendering frames in a game and are now the backbone of AI systems. It’s this industrial use case that is most at risk. Picture a cloud provider renting out GPU resources to all comers. These new attacks demonstrate how, in theory, a single malicious customer could go beyond seizing control of an accelerator to compromise the entire server, access sensitive data, and potentially hack the provider’s entire infrastructure. Let’s break down why this kind of attack is even possible.

Rowhammer in a nutshell

We covered Rowhammer in-depth in previous posts, but here’s the quick version. The original attack was first proposed back in 2014, and it exploits the actual physical properties of RAM chips. Individual memory cells are simple components arranged in tight rows. In theory, reading or writing to one cell shouldn’t affect its neighbors. However, because these chips are packed so densely — with millions or even billions of cells per chip — writing to one spot can sometimes modify the cells next to it.

The 2014 study showed that this isn’t just a recipe for random data corruption; it can be weaponized. By repeatedly accessing (or “hammering”, hence the name) a specific area of memory, an attacker can intentionally flip bits in adjacent cells. If an attacker manages to flip the right bits, he can bypass critical security measures to snag sensitive data or run unauthorized code with full privileges.

Since that first discovery, we’ve seen a constant arms race between new Rowhammer defenses and clever ways to bypass them. We’ve also seen the attack evolve to target newer standards like DDR4 and DDR5. That’s a key takeaway here: for every new type of memory that hits the market, researchers essentially have to reinvent the attack from scratch.

Attacking GDDR6 video memory

The first Rowhammer attack on GPUs was presented back in 2025, but the results were relatively modest. At the time, researchers were able to force bit-flips in GDDR6 memory cells, and show how that data corruption could degrade the performance of an AI system.

These latest papers, however, warn of much more damaging attacks on video memory. Using slightly different techniques, GDDRHammer and GeForge manipulate the page tables — basically the master structures that track where data lives in the GPU’s memory. This enables an attacker to read or write to any part of the video memory, and even reach into the main system RAM managed by the CPU. Modifications to page tables are possible because the researchers have found a way to hammer memory cells much more efficiently. They pulled this off despite the hardware using Target Row Refresh, a core defense designed specifically to stop Rowhammer. TRR detects repeated access to specific cells, and forces a data refresh in the neighboring rows to hamper the attack. However, the researchers discovered a specific pattern of access that can bypass TRR.

How realistic are these GPU attacks?

As is usually the case with this type of research, pulling off these attacks in the real world comes with a lot of contingencies. First off, different GPUs behave differently. For instance, the GeForge attack was significantly more effective on the consumer-grade GeForce RTX 3060. On the industrial-strength Nvidia RTX A6000, the attack’s efficiency dropped by more than five times — even though both cards use the exact same GDDR6 memory standard. Going back to our hypothetical scenario of a malicious cloud customer: for an attack to work, they’d first need to identify exactly which accelerator they’ve been assigned, then profile their exploit specifically for that hardware. In short, this would have to be an incredibly sophisticated and expensive targeted attack.

It’s also worth noting that GDDR6 isn’t the latest and greatest anymore. Consumer devices are moving to GDDR7, while professional-grade hardware often uses high-speed HBM memory. These systems come with ECC (Error Correction Code), a built-in mechanism that checks data integrity. ECC can actually be enabled on cards like the Nvidia A6000; while it might take a small bite out of performance, it effectively makes both of these attacks impossible.

Another tool available to owners of AI-focused servers is enabling the IOMMU (input–output memory management unit) — a system that isolates the GPU’s memory from the CPU’s memory. This will prevent an attack from escalating from the graphics accelerator to the main processor and compromising the entire server. This is where the third study, GPUBreach, comes into play. Its main differentiator from GDDRHammer and GeForge is that it can actually bypass even IOMMU protection! It pulls this off by exploiting some fairly traditional bugs found in NVIDIA drivers.

So, despite the existing hurdles, these three studies prove that Rowhammer attacks remain a potent threat. This is especially true in our current AI boom, which relies on massive, expensive, and potentially vulnerable infrastructure packed with dozens or even hundreds of thousands of computing devices. The Rowhammer timeline goes to show that technical barriers almost never hold for long. In standard RAM, researchers have managed to bypass not only basic fixes like Target Row Refresh, but also more advanced — and theoretically bulletproof — solutions like ECC memory. While the extreme complexity of these exploits means they’ll likely never become a mass-market threat, for anyone running expensive computing systems, they’re definitely a risk factor that can’t be ignored.