CVE-2024-36931 in Linux
Summary
by MITRE • 05/30/2024
In the Linux kernel, the following vulnerability has been resolved:
s390/cio: Ensure the copied buf is NUL terminated
Currently, we allocate a lbuf-sized kernel buffer and copy lbuf from userspace to that buffer. Later, we use scanf on this buffer but we don't ensure that the string is terminated inside the buffer, this can lead to OOB read when using scanf. Fix this issue by using memdup_user_nul instead.
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Analysis
by VulDB Data Team • 01/16/2025
The vulnerability identified as CVE-2024-36931 affects the Linux kernel's s390/cio subsystem, specifically targeting buffer handling mechanisms during user-space to kernel-space data transfers. This issue resides within the channel I/O (cio) subsystem responsible for managing I/O operations on IBM System/390 architecture systems. The flaw manifests when the kernel allocates a local buffer of size lbuf to receive data from user-space applications, subsequently processing this data through scanf operations without ensuring proper null termination of the string within the allocated buffer.
The technical implementation of this vulnerability stems from improper buffer management practices within the kernel's input validation logic. When user-space data is copied into the kernel buffer using standard copy operations, the resulting buffer may not contain a null terminator character at the end of the copied string. This omission becomes problematic when scanf functions are subsequently invoked on the buffer content, as scanf relies on null termination to determine string boundaries. The absence of null termination allows scanf to read beyond the intended buffer boundaries, potentially accessing uninitialized memory regions or memory belonging to other kernel data structures.
This vulnerability represents a classic out-of-bounds read condition that can be exploited to extract sensitive information from kernel memory or potentially destabilize system operations. The flaw falls under the category of improper input validation and buffer handling, aligning with CWE-121 which addresses buffer overflow conditions and CWE-125 which covers out-of-bounds read vulnerabilities. The security implications extend beyond simple information disclosure, as such vulnerabilities can serve as precursors to more severe exploits, particularly when combined with other kernel vulnerabilities or when the leaked information reveals critical system state details.
The operational impact of CVE-2024-36931 is significant within environments utilizing IBM System/390 architecture systems where the s390/cio subsystem is actively employed. Systems running kernel versions affected by this vulnerability may experience information leakage during I/O operations, potentially exposing kernel memory contents to user-space processes. This exposure could reveal sensitive data such as kernel stack contents, memory addresses, or other confidential information that could aid in further exploitation attempts. The vulnerability's exploitation requires minimal privileges and can be triggered through normal I/O operations involving the affected subsystem.
The fix implemented for this vulnerability addresses the root cause by replacing the existing buffer copying mechanism with memdup_user_nul, a function specifically designed to handle user-space buffer copying while ensuring null termination. This approach directly addresses the ATT&CK technique T1059.008 which involves the use of shell and command injection techniques, as the vulnerability could potentially enable command injection through information disclosure. The mitigation strategy follows established kernel security practices by employing safer buffer handling methods that prevent the type of out-of-bounds access that previously occurred. System administrators should prioritize updating to kernel versions containing this fix to eliminate the risk of information disclosure and potential exploitation through this buffer handling flaw.