In 2022, researchers uncovered a significant vulnerability in the SD card upgrade mode of certain devices, tracked as CVE-2022-44563. This vulnerability is a race condition, which means that under certain timing circumstances, malicious code can interfere with a process and achieve unauthorized actions—in this case, leaking confidential data. In this post, we’ll break down how this flaw works, what SD upgrade mode is, show code snippets, discuss exploit methods, and give references for further reading.

What’s SD Upgrade Mode?

SD upgrade mode is a special boot state in many embedded devices, where the device reads special files from an SD card in order to upgrade firmware or restore software. This is a trusted operation, and the expectation is that only known, good files are read and applied.

The Race Condition Explained

A *race condition* vulnerability happens when two or more operations run at the same time and interact in a way the designer didn’t expect. In the case of CVE-2022-44563, when the device is in SD upgrade mode, there’s a narrow moment when the system verifies the integrity of a file before actually performing the operation with that file.

Here’s a simplified version of what happens

// Pseudocode illustrating the flaw

open(file);
if (verify_signature(file)) {
    // TIME WINDOW: file can be changed here!
    read_and_apply_file(file);
}


In this gap—between verifying the signature and actually using the file—a malicious actor can swap the file on the SD card. The system will then trust the now-swapped file, as it assumes the previously verified file is still present, leading to privilege escalation or data leakage.

Trigger Upgrade: SD upgrade mode is initiated—by physical access or sometimes remotely.

3. File Swap: When the system opens and verifies the good file, the attacker times their action to quickly replace the file with the malicious one.

4. Execution: The system, thinking the file is validated, proceeds to read and execute/apply the malicious file.

5. Data Leak: The payload in the malicious file reads sensitive info and writes it back to the SD card or sends over a network.

Example Exploit Code

While real-world exploitation requires precise timing (sometimes hard to do remotely), here’s a concept in pseudo-shell code using Linux tools:

# Prepare good.bin (valid, signed) and bad.bin (malicious)
# Use inotifywait (Linux tool) to watch for read events

inotifywait -m /mnt/sdcard/good.bin -e open |
while read; do
    cp bad.bin /mnt/sdcard/good.bin
done


This watches for when the device opens good.bin. When that happens, it immediately replaces it with bad.bin—hopefully, right in the vulnerable time window.

The malicious file could contain code that copies private configuration files, user data, or keys from the system:

#!/bin/sh
cp /etc/shadow /mnt/sdcard/leaked_shadow


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Why Is This a Big Deal?

This bug can break data confidentiality—meaning private data stored on your device can be stolen. It’s more likely to be exploited in situations where physical SD card access is possible (e.g. lost, stolen devices, or maintenance scenarios), but sometimes remote exploitation can be engineered if there’s SD upgrade mode exposure.

Mitigating this is about closing the window for the race condition

- Re-verify the file after loading, or lock the file descriptor, so the file can’t be swapped between verification and use.

References for Further Reading

- Official CVE Record for CVE-2022-44563
- Google Project Zero: Race Conditions Explained
- Common Race Condition Vulnerabilities
- inotifywait man page
- Race Condition Exploit Techniques (YouTube)

Conclusion

CVE-2022-44563 is a clear reminder that even the most trusted system operations—like firmware upgrades—need robust security. Race conditions are tricky, often subtle, and can lead to unexpected critical data leaks. Always have proper checks in place, especially when handling files from removable storage under sensitive circumstances.

Share this post to keep your team aware of subtle attack vectors in embedded firmware!

Timeline

Published on: 11/09/2022 21:15:00 UTC
Last modified on: 11/10/2022 13:56:00 UTC