CVE-2024-20154 - Critical Out-of-Bounds Write in Modem Firmware

Summary: In June 2024, security researchers identified a severe vulnerability (CVE-2024-20154) affecting modem firmware used in many smartphones and IoT devices. The flaw is due to a missing bounds check that allows out-of-bounds memory write – making it a prime candidate for remote code execution (RCE). Alarmingly, exploitation requires no user interaction and no elevated permissions. Attackers only need to lure a victim’s device to connect to a rogue base station, placing millions of devices at risk.

What Is CVE-2024-20154?

CVE-2024-20154 is a vulnerability discovered in the modem firmware integrated into several mobile devices. Specifically, the flaw resides in the way the modem processes certain network messages (e.g., through LTE or 5G baseband protocols). A missing bounds check in the handling of these messages makes it possible to write data beyond the intended memory buffer, potentially overwriting critical structures and hijacking device execution flow.

How Does the Vulnerability Work?

The vulnerable code fails to check if data being copied into a memory buffer fits in the allocated space. This classic out-of-bounds write can be exploited remotely – *before* the data ever reaches the device’s normal Android, iOS, or Linux OS.

Here’s a pseudocode illustrating the vulnerable part

#define MAX_DATA 512

void handle_network_message(char *data, int length) {
    char buffer[MAX_DATA];
    // Missing check: should ensure length <= MAX_DATA
    memcpy(buffer, data, length);
    ...
}

What’s wrong?
If the attacker sends a length argument larger than 512 bytes, the memcpy function will overwrite memory *past* buffer, possibly controlling code execution.

Setup a Rogue Base Station.

Using open-source tools like srsLTE or OpenBTS, the attacker sets up a fake LTE/5G base station.

Target a UE (User Equipment) Device.

When a victim’s device (phone, IoT device) attempts to connect, the rogue base station sends specially crafted network messages triggering the vulnerable handler in the modem firmware.

The attacker jams an overlong message, causing the modem to overwrite its memory.

4. Hijack Control Flow / Achieve RCE.
By precisely crafting the overflow, the attacker can overwrite critical function pointers or return addresses, leading to execution of code injected in the rogue message. This code runs with the privileges of the modem firmware, often *below* the main OS (so even OS-level protections won’t help).

No user action is required beyond the device connecting to the rogue cell (which can be done passively in real world scenarios).

How Serious Is This?

- Remote code execution in modem firmware is one of the most powerful attacks: it can implant persistent malware, steal secrets, track users, or even enable remote wiretapping.
- The vulnerability exists *below* the operating system – bypassing most standard security protections.

Detection and Mitigation

- Patch: Device manufacturers using MediaTek (or other impacted brands) should apply Patch ID *MOLY00720348* immediately. Check with your vendor/carrier for official firmware updates.
- Prevention: Do not connect to unknown or suspicious mobile networks, especially in high-risk areas or during security conferences.

Proof-of-Concept (PoC) Snippet

Here’s a simplified, illustrative Python snippet showing how an attacker could trigger the overflow in a testbed:

# Pseudo code for a rogue LTE base station sending overlong messages

def send_crafted_message():
    # Construct malicious message larger than modem expects
    message = b"A" * 1024  # Overflows 512-byte buffer
    length = len(message)
    # Send to device via rogue base station interface
    rogue_base_station.send_network_message(message, length)

*Note: Real-world exploitation requires specialized hardware and knowledge of baseband protocol details.*

References and Further Reading

- Original CVE Record
- MediaTek Security Bulletins
- Baseband Attacks Explained – Project Zero
- Open-Source Fake Base Station Tools

Conclusion

CVE-2024-20154 is a prime example of how deeply-buried firmware vulnerabilities, especially in modem or baseband code, can undermine device security. It shows that even with a locked-down operating system, a sophisticated attacker with the right tools can sidestep protections – just by exploiting wireless protocols. As always, update your devices as soon as fixes are available and consider disabling automatic mobile network selection, especially in hostile environments.

Timeline

Published on: 01/06/2025 04:15:07 UTC
Last modified on: 01/06/2025 15:15:13 UTC