CVE-2023-21492: Kernel Pointers Leakage in Log File Prior to SMR May-2023 Release 1, Allowing a Privileged Local Attacker to Bypass ASLR

A recently discovered vulnerability (tagged as CVE-2023-21492) has been identified that allows a privileged local attacker to bypass Address Space Layout Randomization (ASLR). This vulnerability specifically impacts systems using the kernel version prior to SMR May-2023 Release 1. The vulnerability exists due to the kernel inadvertently disclosing kernel pointers in log files, which can pave the way for an attacker to exploit the ASLR protection mechanism. In this blog post, we will discuss the details of the vulnerability, the code snippet in question, the original references, and potential exploit details.

Vulnerability Details

Address Space Layout Randomization (ASLR) is a crucial security feature in modern operating systems, responsible for randomizing the memory layout to make it more difficult for attackers to predict the addresses they need to target in their exploits. This is helpful in mitigating attacks, such as buffer overflows and code execution attempts.

The discovered vulnerability (CVE-2023-21492) specifically revolves around the leakage of kernel pointers in log files generated by the affected systems. A privileged local attacker could, in turn, use these leaked kernel pointers to bypass the ASLR protection mechanism, thereby exploiting the system more easily.

Code Snippet

Below is a representative code snippet highlighting the kernel pointer leakage issue. The leakage occurs due to incorrect usage of a macro function:

...
    /* Print kernel pointers in log file */
    printk(KERN_INFO "Function Address: %p\n", function_address);
    printk(KERN_INFO "Buffer Address: %p\n", buffer_address);
...

The above code prints the kernel pointers (function_address and buffer_address) in the log file using the printk function, which, when accessed by a privileged attacker, can reveal crucial information related to the kernel address space layout.

The vulnerability has been officially acknowledged and documented in the following references

1. CVE-2023-21492 - Official CVE entry in the MITRE database
2. Kernel Pointers Disclosure Advisory - Security advisory published by the affected vendor
3. SMR May-2023 Release 1 Patch Notes - Patch notes detailing the specific kernel versions addressing this vulnerability

Exploit Details

To exploit this vulnerability, an attacker would need privileged local access to the system, as the leaked kernel pointers are typically accessible only by users with administrative or superuser privileges. Once the attacker has access to the log files containing leaked kernel pointers, they can de-randomize the ASLR and accurately target specific memory addresses. This process may facilitate further attacks, such as privilege escalation, code execution, or unauthorized access to sensitive information.

Mitigation

It is strongly advised to update the kernel to the latest version (SMR May-2023 Release 1 onwards), as it resolves CVE-2023-21492. Additionally, system administrators can restrict access to log files, ensuring only trusted users with appropriate privileges can view kernel logs.

Conclusion

CVE-2023-21492 underscores the significance of keeping systems up-to-date and maintaining robust access controls to protect sensitive system information. Regularly updating your kernel and closely monitoring access to log files will go a long way in mitigating vulnerabilities like this and maintaining a secure computing environment.

Timeline

Published on: 05/04/2023 21:15:00 UTC
Last modified on: 05/10/2023 18:25:00 UTC