A vulnerability (CVE-2024-54507) was discovered in the XNU kernel, affecting macOS and iOS, which allows malicious actors to leak kernel memory. The flaw resides in the sysctl interface, specifically the kern.hv_vmm_vcpu_state handler. This handler failed to properly validate the size of the buffer provided by the user, resulting in an out-of-bounds read. By crafting a request with a larger buffer than expected, an attacker could read data beyond the intended memory region, potentially exposing sensitive kernel information. This vulnerability was patched by Apple in October 2024 and is relatively simple to exploit.
The blog post by Jann Horn, titled "Susctl CVE-2024-54507: A particularly 'sus' sysctl in the XNU kernel," details a vulnerability (CVE-2024-54507) discovered in Apple's XNU kernel, impacting macOS and iOS. This vulnerability stems from improper handling of the kern.sysctlbyname sysctl, specifically when dealing with nested structures within sysctl MIBs (Management Information Bases).
Horn explains that kern.sysctlbyname allows userspace programs to access kernel data structures by specifying a name-based path, akin to navigating a file system. The issue arises when a MIB entry points to a structure containing further nested structures or pointers. Normally, sysctlbyname should only allow access to the top-level structure specified in the MIB. However, the flawed implementation permitted traversing deeper into these nested structures by simply appending the names of the inner members to the sysctl name, even if those inner members weren't explicitly exposed by any MIB entry.
This effectively bypassed intended access restrictions, granting access to kernel memory regions that should have been inaccessible to userspace. The specific example provided in the post demonstrates reading the version field of an embedded os_unfair_lock structure within another structure exposed via a sysctl. Although this example only disclosed kernel version information, Horn highlights that this vulnerability could potentially be exploited to leak more sensitive data or even achieve arbitrary memory read, depending on the structures accessible through vulnerable sysctl entries.
The post delves into the technical details of the vulnerability, explaining how the kernel's internal sysctl_name function mishandled the traversal of these nested structures. It misinterprets the presence of a sub-structure within a returned buffer as an indicator that further traversal is permissible, even if no MIB entry exists for the sub-structure. This logic flaw allows an attacker to construct arbitrary paths by appending the names of nested members, essentially crafting a "fake" MIB entry on the fly.
Horn's analysis includes a detailed breakdown of the vulnerable code path within the kernel, illustrating the faulty logic. He further illustrates the exploitation process by showcasing a proof-of-concept code snippet that successfully reads the version field of the nested os_unfair_lock structure. The post concludes by mentioning that Apple has addressed this vulnerability in their security updates and encourages users to update their systems. The fix likely involves restricting traversal beyond the top-level structure specified in the MIB, preventing access to nested members not explicitly exposed.
Summary of Comments ( 8 )
https://news.ycombinator.com/item?id=42808801
Hacker News commenters discuss the CVE-2024-54507 vulnerability, focusing on the unusual nature of the vulnerable sysctl and the potential implications. Several express surprise at the existence of a sysctl that directly modifies kernel memory, questioning why such a mechanism exists and speculating about its intended purpose. Some highlight the severity of the vulnerability, emphasizing the ease of exploitation and the potential for privilege escalation. Others note the fortunate aspect of the bug manifesting as a kernel panic rather than silent memory corruption, making detection easier. The limited practical impact due to System Integrity Protection (SIP) is also mentioned, alongside the difficulty of exploiting the vulnerability remotely. A few commenters also delve into the technical details of the exploit, discussing the specific memory manipulation involved and the resulting kernel crash. The overall sentiment reflects concern about the unusual nature of the vulnerability and its potential implications, even with the mitigating factors.
The Hacker News post discussing the CVE-2024-54507 vulnerability in the XNU kernel, titled "Susctl CVE-2024-54507: A particularly 'sus' sysctl in the XNU kernel," has generated several comments.
Many commenters focus on the unusual nature of the vulnerability and its exploitation. One commenter points out the irony of a vulnerability existing in a mechanism designed to improve security, specifically the
sysctlinterface intended for secure configuration adjustments. They express surprise that such a fundamental component could be susceptible to this type of issue.Another commenter delves into the technical details of the exploit, highlighting the unexpected behavior of the
sysctlhandler. They discuss how the vulnerability arises from an incorrect handling of specific input, leading to a kernel panic. The comment emphasizes the severity of the issue, as it can be triggered remotely, potentially allowing for denial-of-service attacks.Several commenters also discuss the implications of the vulnerability for Apple users. Some express concern about the potential impact on macOS and iOS devices, given the widespread use of the XNU kernel. Others raise questions about the timeline for a patch and the potential for exploitation in the wild.
A few comments touch on the broader security implications of this type of vulnerability. One commenter notes the increasing complexity of modern operating systems and the challenges of ensuring their security. They suggest that this vulnerability highlights the need for more robust security testing and validation processes.
Some of the more technically inclined comments delve into the specifics of the kernel code and the mechanisms that led to the vulnerability. These comments offer insights into the inner workings of the XNU kernel and provide a deeper understanding of the exploit's technical details.
A couple of commenters also discuss the responsible disclosure process and commend the researchers for reporting the vulnerability to Apple before publicly disclosing it. They emphasize the importance of responsible disclosure in mitigating the potential impact of security vulnerabilities.
Overall, the comments on the Hacker News post reflect a mixture of surprise, concern, and technical analysis. The commenters acknowledge the severity of the vulnerability and its potential impact on Apple users, while also delving into the technical intricacies of the exploit and its implications for kernel security.