Description

CVE-2021-215551, a collection of five vulnerabilities in Dell computer drivers, was discovered and fixed in May 2021, after a 12-year period of exploitability. However, according to reports, Dell's fix was limited to administrative users and did not address the write-what-where vulnerability, making it an excellent option for future Bring Your Own Vulnerable Driver (BYOVD) attacks. Bring Your Own Vulnerable Driver (BYOVD) attacks is an attack technique in which threat actors drop a legitimate vulnerable driver on targeted systems. Additionally, even Microsoft's strict Windows DSE (Driver Signature Enforcement) rules failed to prevent these attacks. Dell's 'dbutil 2 3.sys' driver is reportedly vulnerable to CVE-2021-21551, and the write-what-where condition persists in dbutil 2 3.sys, dbutildrv2.sys, and dbutildrv2.sys (version 2.5 and 2.7). These three vulnerable signed drivers can be used by attackers to execute kernel code. Threat actors still require administrator access to exploit the vulnerability (CVE-2021-21551), but high-skilled actors can attack in kernel mode, or ring 0, the maximum privilege on Windows systems. Attackers can install UEFI rootkits, execute targeted commands, and sustain persistence on infected machines after successful exploitation. Researchers reported the vulnerability to Dell, the company states that, after a thorough review, it is classified a weakness rather than a flaw owing to the privilege level required to launch an attack, and that it is not yet intended to publish a security advisory for the issue.