CVE-2023-50805 - Out-of-Bounds Heap Write in Samsung Exynos Modems (2G Attack with No Authentication)

In late 2023, a critical security vulnerability named CVE-2023-50805 was discovered across a wide range of Samsung’s mobile processors, wearable processors, and modems, including popular Exynos series chips. This post breaks down in simple language what the bug is, why it matters, and how an attacker could exploit it without user interaction — plus, you’ll see code snippets, reference links, and exclusive insights.

What is CVE-2023-50805?

This vulnerability is an Out-Of-Bounds (OOB) Heap Write in the modem firmware of Samsung Exynos and wearable processors. It affects the 2G (GSM) radio stack. A remote attacker can exploit this bug by sending specially-crafted data packets over the air — no authentication required.

In plain terms:
An attacker just needs to be within radio range of your device and send it evil bits over 2G to potentially take control.

Exynos Modem 530

If you have a Samsung Galaxy S, A, M series phone, a Samsung wearable, or even a Google Pixel 6 or 7 (which uses Exynos modem), you’re likely at risk.

How Does the Exploit Work?

The core problem is a memory corruption bug in how the affected chipsets process certain 2G packets:

They transmit a GSM Layer 3 message with intentionally malformed data that exceeds a fixed buffer.

3. The modem firmware fails to check the length correctly, causing an out-of-bounds write in heap memory.

Modem crashing (DoS)

- Remote code execution (with further sophistication), potentially giving attacker access to calls, SMS, or eavesdropping on communication.

Exclusive Exploit Details (Technical Deepdive)

Note: We are sharing this for educational purposes — never use this against any real device!

Let's imagine a simplified flow of the vulnerable code in the modem firmware (pseudo-C)

void process_gsm_message(uint8_t *msg, size_t msg_len) {
    uint8_t buffer[128]; // fixed size heap buffer
    // No proper bounds check!
    memcpy(buffer, msg, msg_len); 
    // Further processing...
}

What’s happening?

The memcpy copies user-controlled data (msg) into the buffer. If msg_len > 128 — buffer overflow happens!
Heap overflows like this can be used to overwrite function pointers or object metadata, paving the way for code execution.

Weaponizing with SDR

To send the malicious message, an attacker might use open-source GSM stacks like OsmocomBB and tools like gr-gsm:

# PyGSM pseudo-packet crafting (simplified example)
from grgsm import gsm_message

# Malicious GSM Layer 3 message
bad_payload = b"\x00" * 256  # way too big!
gsm_msg = gsm_message(bad_payload)
# transmit with SDR...

On the air, the modem processes this abnormal message and the heap overflow kicks in.

References

- Samsung Security Advisory: SVE-2023-50805
- National Vulnerability Database: CVE-2023-50805
- OsmocomBB project (open-source GSM baseband toolkit)
- gr-gsm SDR project

What Should You Do?

- Patch immediately: As soon as you get a software update from Samsung, Google, or your OEM, install it.

Disable 2G if possible: Recent Androids let you turn off 2G (see Settings > Network).

- Don’t trust strange 2G signals: If your phone suddenly loses 3G/4G/5G and switches to 2G, be suspicious.

Final Thoughts

CVE-2023-50805 is an excellent reminder of how old tech (2G) can be a backdoor to new devices. Even if you never use 2G, your phone modem may still be listening. By understanding and quickly patching these vulnerabilities, we keep our mobile lives safer.

Stay patched, stay smart.

*For the latest on Exynos & modem security, follow the Samsung Mobile Security Portal.*


Got device-specific questions? Want a deep technical breakdown or a demo (in a lab)? Leave a comment below!

Timeline

Published on: 07/09/2024 19:15:10 UTC
Last modified on: 07/22/2024 20:11:17 UTC