Integrity Validation Bypass in CryptoPro Secure Disk for BitLocker

Summary

The CPSD CryptoPro Secure Disk application boots a small Linux operating system to perform user authentication before using BitLocker to decrypt the Windows partition. The system is located on a separate unencrypted partition which can be reached by anyone with access to the hard disk. Multiple checks are performed to validate the integrity of the Linux operating system and the CryptoPro Secure Disk application files. When files are changed an error is shown on system start. One of the checks is the Linux kernel's Integrity Measurement Architecture (IMA). It was identified that configuration files are not validated by the IMA and can then (if not checked by other measures) be changed. This allows an attacker to execute arbitrary code in the context of the root user and enables an attacker to e.g., plant a backdoor and access data during execution.