Hostile SIMs exploit spec-compliant commands

In a finding that could rewire how the mobile industry thinks about SIM card security, researchers have demonstrated that a malicious SIM can command a phone to leak data, downgrade its connection to 2G, or even execute code—all by abusing standardized features that are supposed to be there.

Presented at the USENIX WOOT conference in Baltimore this week, the research examines proactive SIM functionality, which allows a SIM to issue commands to the device hosting it. Among those commands is RUN AT, which lets the SIM request execution of AT commands—an instruction set that has controlled modems since the 1980s. Put that capability into hostile hands, and the attack surface widens considerably.

CATANA: A Toolkit to Probe SIM Attack Surface

Tomasz Piotr Lisowski and Marius Muench of the University of Birmingham, working with Kristian Covic from Fuzzware, developed a toolkit called CATANA to explore what a malicious SIM could achieve. Their goal was to systematically test whether the proactive SIM interface could be abused, and if so, to what extent.

The team tested 26 devices: 18 smartphones and eight IoT modems. They found that nine exposed an AT command interface to the SIM. The IoT devices were especially accommodating—seven of the eight modems exposed it. This asymmetric exposure suggests that while smartphone vendors have increasingly locked down the interface, the IoT world remains far more permissive.

Four Vulnerabilities Uncovered

Through their testing, the researchers identified four distinct vulnerabilities and demonstrated practical attacks including code execution, arbitrary file reads, denial of service, and downgrading connections to 2G. Each of these attacks leverages the proactive SIM functionality that is explicitly defined in cellular specifications.

“The fascinating part here is that the proactive capabilities of a SIM and the resulting attack surface is explicitly defined in the technical specifications for cellular communication,” said Muench, making the attacks “specification-compliant.” He also noted that hostile SIMs are still absent from many threat models, despite earlier research and leaked intelligence documents demonstrating the risks.

Real-World Exploits: From EV Chargers to File Theft

The researchers didn't stop at theoretical analysis. They put the method to work on an Autel EV charger fitted with a Quectel EC25-AFX cellular module. By sending commands from the SIM, they exploited a command injection bug in the modem's Linux-based application processor and achieved code execution.

On an Oppo Reno14 F 5G, they uncovered 198 AT commands and variants available through the SIM interface. Some could power down the handset, kill its modem, or force it back to 2G. That last trick proved especially stubborn: toggling airplane mode, disabling the SIM, and changing the phone's network settings all failed to reverse the downgrade.

They also demonstrated file theft against a Quectel EG25-G modem. By combining a malicious symbolic link with SIM-originating commands, they were able to email a targeted file to an attacker-controlled server.

Attack Prerequisites: Control of the SIM

Before you start eyeing your SIM tray suspiciously, there is a catch: the attacks require control of the SIM itself. That could come through compromised SIM software, physical tampering, abuse of remote administration by a malicious or breached operator, or supply chain shenanigans.

In other words, these are not remote attacks that can be launched over the air. An attacker needs to have already planted a malicious SIM in the victim's device, which is a significant practical hurdle but not an impossible one—especially in scenarios involving physical access or compromised supply chains.

Android Flaw and Patching Timeline

The researchers also discovered that vulnerable versions of Android allowed a hostile SIM to invoke the standardized LAUNCH BROWSER command, which could open an attacker-controlled website without user interaction, even while the phone was locked. Google tracked this as CVE-2025-48618 and patched Android 13 through 16 in December 2025.

The patch was part of Google's regular Android security update process. Users on those versions who have not applied the December 2025 update remain exposed to this particular vector, though the broader range of attacks demonstrated may affect a wider set of devices.

Disclosures and Industry Response

The researchers disclosed their findings to Google, Oppo, Quectel, Semtech, and Qualcomm in March, followed by the GSMA in May. Qualcomm has since produced a hardened configuration that disables the SIM AT interface by default. The GSMA is tracking the wider issue as CVD-2026-0122.

These steps represent a first line of defense, but the researchers believe the most durable fix lies elsewhere: retiring RUN AT and other risky proactive SIM functionality altogether. Modern smartphones appear to have largely gotten the memo—the low exposure rate among handsets suggests some vendors have already moved away from this risky interface. The IoT world, however, still has a ways to go.

What This Means for the Ecosystem

The findings carry significant implications for anyone who relies on cellular-connected devices—which, these days, is nearly everyone. For consumers, the threat may seem abstract, but the persistence of the 2G downgrade is particularly concerning: it suggests an attacker could force a device onto a legacy network with weaker encryption, making interception easier.

For enterprises deploying IoT devices, the risk is more concrete. The researchers' success against an EV charger demonstrates that these attacks can have physical-world consequences, potentially affecting critical infrastructure or industrial systems. The fact that 2G downgrades resisted common countermeasures suggests that a determined attacker could achieve a persistent degradation of security.

While the practical difficulty of planting a malicious SIM offers some reassurance, the specification-compliant nature of the attacks means they're likely to persist unless the industry takes proactive steps. The GSMA's tracking of the issue and Qualcomm's hardened configuration are positive signs, but the researchers' call to retire RUN AT outright may be the only definitive solution—one that would require broad industry coordination to implement.