A critical vulnerability was discovered in the lib/kobject.c file in the Linux kernel, versions before 6.2.3. The vulnerability, assigned as CVE-2023-45863, allows attackers with root access to trigger a race condition resulting in a critical out-of-bounds write via the fill_kobj_path function. Researchers have observed the exploit in the wild and published various proofs-of-concept demonstrating how attackers can exploit this vulnerability. This post will go into further detail on the vulnerability's consequences, as well as ways to mitigate the risk.

Vulnerability Details

The Linux kernel is the core of the operating system and is responsible for various system calls, process control, and memory management. It contains numerous libraries and functions to facilitate its purpose, including lib/kobject.c - a library file handling kernel objects and portions of the sysfs pseudo filesystem.

The vulnerability resides in the fill_kobj_path function of lib/kobject.c. This function attempts to find the path to a kernel object by concatenating the names of the parent objects that make up the filesystem hierarchy. However, due to insufficient input validation and locking, a race condition occurs. An attacker with root access can exploit this race condition to trigger a buffer overflow, leading to an out-of-bounds write.

Code Snippet

The following code snippet demonstrates the vulnerable portion of the fill_kobj_path function in lib/kobject.c:

ssize_t fill_kobj_path(struct kobject *kobj, char *buffer, ssize_t buflen)
{
    ssize_t len;

    buffer += buflen;
    *--buffer = '\';
    buflen--;

    for (; kobj&&buflen; kobj = kobj->parent) {
        len = sysfs_slashed_kobj_name(kobj, object_name(kobj));
        if (buflen <= len) {
            buflen = -ERANGE;
            break;
        }
        buffer -= len;
        buflen -= len;
        memcpy(buffer, object_name(kobj), len);
        *--buffer = '/';
    }
    return buflen;
}

Original References

- Linux Kernel Source Code
- kernel commit fixing the vulnerability in versions 6.2.3 and later.
- Vulnerability Disclosure on the CVE List

Exploit Details

To exploit this vulnerability, an attacker must begin by obtaining root access on the target system. After gaining root access, the attacker can then craft a malicious sysfs path. The attacker will use this path to trigger the said race condition, which will cause a buffer overflow. This buffer overflow will, in turn, lead to an out-of-bounds write.

The consequences of exploiting this vulnerability are severe. Out-of-bounds writes can result in arbitrary code execution, leading to the complete compromise of the system. Moreover, an attacker with root access can use this security flaw to elevate privileges, further compromising the target.

Mitigation and Conclusion

To mitigate this vulnerability, users should update their Linux kernel to version 6.2.3 or later, which contains a patch to address this issue. Researchers also recommend implementing strict access control policies, only granting root access to trusted users. Regularly monitoring system logs for any signs of unauthorized access can further help to minimize the risk of this vulnerability being exploited.

In conclusion, CVE-2023-45863 is a critical security flaw affecting the Linux kernel. Users and system administrators must be vigilant in taking the necessary steps to protect their systems against this vulnerability, ensuring that their software is up-to-date and monitoring for unauthorized access. Moreover, being aware of this vulnerability and engaging in responsible disclosure practices can help contribute to a safer and more secure digital landscape.

Timeline

Published on: 10/14/2023 21:15:45 UTC
Last modified on: 10/19/2023 13:12:23 UTC