Overview
The vulnerability CVE-2023-4818 is a critical security flaw found in the PAX A920 device that allows attackers to downgrade the bootloader, potentially compromising the entire system. This vulnerability is particularly significant as it could lead to a total system takeover or data leakage if exploited successfully. With a CVSS score of 7.6, it’s of high severity and demands immediate attention.
Vulnerability Summary
CVE ID: CVE-2023-4818
Severity: High (CVSS: 7.6)
Attack Vector: Physical
Privileges Required: None
User Interaction: Required
Impact: Potential system compromise or data leakage
Affected Products
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Product | Affected Versions
PAX A920 Device | All versions to date
How the Exploit Works
The exploit takes advantage of a bug in the version check of the PAX A920 device’s bootloader. An attacker with physical USB access to the device can downgrade the bootloader to a version with known vulnerabilities. Although the signature is correctly checked, and only a bootloader signed by PAX can be used, the version check bug allows for the installation of older, vulnerable bootloaders, making the system susceptible to further attacks.
Conceptual Example Code
Although it is not a real exploit code, the below conceptual example illustrates how an attacker might use a USB device to exploit this vulnerability:
# On the attacker's machine
$ dd if=vulnerable_bootloader.img of=/dev/sdX
# On the target PAX A920 device
$ mount /dev/sdX /mnt
$ cp /mnt/vulnerable_bootloader.img /boot
$ rebootIn this example, `vulnerable_bootloader.img` refers to an older, vulnerable version of the bootloader signed by PAX. The `dd` command writes this image to a USB device (`/dev/sdX`) on the attacker’s machine. The attacker then connects this USB device to the target PAX A920 device, copies the vulnerable bootloader image to the `/boot` directory, and reboots the system. Upon reboot, the target device uses the vulnerable bootloader, rendering it susceptible to further attacks.
