CVE-2022-21499: Restricting Kernel Debuggers KGDB and KDB during Lockdown to Prevent Unauthorized Access

CVE-2022-21499 highlights a security vulnerability in the Linux kernel debuggers KGDB and KDB, which allow unauthorized read and write access to kernel memory during lockdown mode. This vulnerability can be exploited by an attacker with access to a serial port, potentially leading to issues with confidentiality, integrity, and availability.

To address this vulnerability, it is essential that these debuggers respect the lockdown mode when/if triggered. The CVSS 3.1 Base Score for this vulnerability is 6.5, while the CVSS Vector is (CVSS:3.1/AV:L/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:H).

Code Snippet

Before diving into the details of the exploit, let's take a look at a simple example code snippet that demonstrates this kernel lockdown bypass vulnerability:

#include <linux/kernel.h>
#include <linux/kdb.h>
#include <linux/kgdb.h>

// Function to trigger KGDB or KDB during lockdown
void trigger_debugger(void) {
    if (!kernel_is_locked_down()) {
        pr_info("Kernel is not locked down; allow debugger access.\n");
        kdb(KDB_REASON_ENTER,1,NULL);
        kgdb_breakpoint();
    } else {
        pr_info("Kernel is locked down; restrict debugger access.\n");
    }
}

This code snippet defines a function trigger_debugger() that attempts to trigger KGDB or KDB debuggers. However, it only allows debugger access if the kernel is not locked down.

Exploit Details

The primary issue with this vulnerability is that the KGDB and KDB debuggers, which are typically used to diagnose kernel problems, could provide an attacker with unauthorized access to kernel memory if not properly restricted during lockdown mode. An attacker with access to a serial port could trigger the debuggers and perform various actions, such as reading kernel memory or modifying kernel structures, leading to confidentiality, integrity, and availability concerns.

To address this vulnerability, the Linux kernel developers have implemented changes to ensure that kernel debuggers KGDB and KDB respect the lockdown status. This includes restricting KGDB and KDB functionality during lockdown mode, as well as preventing the direct access of kernel memory by limiting it to only read-only or invalidating specific memory regions.

Here are some original references for further reading on this vulnerability

1. CVE-2022-21499 Details - NIST National Vulnerability Database (NVD)
2. KGDB Documentation - Kernel.org
3. KDB Documentation - Kernel.org
4. Lockdown Documentation - Kernel.org

Conclusion

In conclusion, if you are using a Linux system with kernel debuggers KGDB or KDB, it is crucial to ensure that these debuggers are restricted during lockdown mode to prevent unauthorized read and write access to kernel memory. By addressing this vulnerability (CVE-2022-21499), you can better protect your system from potential security threats and maintain the confidentiality, integrity, and availability of your information.

Timeline

Published on: 06/09/2022 21:15:00 UTC
Last modified on: 06/17/2022 14:55:00 UTC