Researchers from the University of Birmingham and Fuzzware demonstrated that a malicious SIM card can use the standard proactive SIM commands mechanism to send AT commands to the modem, which in some cases leads to arbitrary code execution, file reading, disruption of connectivity, and forced downgrade of the device to 2G mode. Of the 26 tested devices — 18 smartphones and 8 IoT modems — the vulnerable interface was accessible on nine: six modems and three smartphones. The issue has been assigned identifiers CVE-2026-57550 (Qualcomm) and CVD-2026-0122 (GSMA). According to the researchers, the highest risk is posed by unattended IoT devices such as EV charging stations, industrial routers, and telematics modules.
Attack mechanism: standard, not a bug
The problem is based on the RUN AT command from the proactive SIM commands set — a mechanism that allows the SIM card to initiate actions on the device. According to the researchers, this command instructs the modem to execute an arbitrary AT instruction, and this is not an undocumented feature but part of cellular specifications. AT commands are a set of instructions for controlling the modem that has existed since the 1980s and has been repeatedly extended by equipment manufacturers.
For systematic testing, the researchers created the CATana toolkit, which determines which AT commands a SIM card can send to a specific modem and what the consequences will be. Among the vulnerable smartphones were the Oppo Find X5, Oppo Reno 14 F 5G, and Asus Zenfone 9. Of the eight tested IoT modems, six exposed the AT interface to the SIM card.
Attack demonstrations: from code execution to file theft
Arbitrary code execution on a charging station
The most critical attack was demonstrated on a commercial Autel charging station with a Quectel EC25-AFX module. By exploiting a command injection vulnerability in the modem’s Linux environment, the researchers achieved arbitrary code execution. This means that an attacker who gains control over the SIM card in such a device could potentially fully compromise it.
Forced downgrade to 2G
On an Oppo Reno 14 F 5G smartphone, 198 AT commands and their variants turned out to be accessible via the SIM card. Among them were commands to power off the device, disable the modem, and force a switch to 2G. According to the researchers, the forced downgrade to 2G persisted even after enabling airplane mode, disabling the SIM card, and changing network settings. Since 2G lacks mutual authentication, such a downgrade significantly simplifies attacks using fake base stations.
Reading and exfiltrating files
A separate exploit made it possible to read arbitrary files from a Quectel EG25-G module and send them to a remote server using the AT+QSMTP command. However, a malicious SIM card alone was not enough for this attack: a specially crafted symbolic link had to be present in the module’s file system in advance.
Opening a website on a locked smartphone
The researchers also point to a related issue: a malicious SIM card was able, without user interaction, to open an attacker-controlled website even on a locked Android smartphone, including Pixel 6, Pixel 8, and Pixel 9 models. This bug, identified as CVE-2025-48618, was fixed by Google in the Android security bulletin for December 2025, although rollout of updates to Android devices remains uneven.
Impact assessment and SIM compromise vectors
To carry out the attack, the attacker must control the SIM card. According to the researchers, this can be achieved in several ways:
- Physical replacement of the SIM card in the device
- Software compromise of the SIM card
- Injection of malicious code at the manufacturing stage
- Gaining control via a hacked or malicious mobile operator
This is why unattended IoT devices with a physically accessible SIM slot are, in the researchers’ view, the most attractive targets. Charging stations, industrial routers, and automotive telematics systems are often installed in locations with limited physical access control, and their SIM cards are rarely inspected.
It is important to emphasize that at this time there are no confirmed cases of these vulnerabilities being exploited in real-world attacks. All demonstrations were performed as research proof-of-concept.
Vendor response and recommendations
The researchers notified Google, Oppo, Quectel, Semtech, and Qualcomm in March 2026, and GSMA in May. Current response status:
- Qualcomm has prepared a protection mechanism that disables SIM card access to AT commands by default
- Quectel reported that it fixed the file-reading issue but is continuing work on eliminating access to the AT interface itself
- Google fixed CVE-2025-48618 in December 2025
For organizations operating IoT devices with cellular modems, the following is recommended:
- Audit the physical accessibility of SIM slots on unattended equipment and restrict access where necessary
- Request information from modem vendors about support for the RUN AT command and options for disabling it
- For devices based on Qualcomm chipsets, apply firmware updates that disable SIM access to AT commands by default as soon as they become available
- For Android devices, ensure the December 2025 security patch or a newer one is installed
- Consider using SIM cards from trusted operators with controlled supply chains for mission-critical IoT equipment
This research highlights a systemic problem: the standardized proactive SIM commands mechanism embedded in cellular specifications turns the SIM card into a full-fledged attack vector against the modem and, through it, the entire device. Organizations with fleets of cellular IoT equipment should already be assessing the physical security of SIM slots and planning modem firmware updates as Qualcomm and Quectel patches become available.
