CVE-2023-5941 in FreeBSD
Summary
by MITRE • 11/08/2023
In versions of FreeBSD 12.4-RELEASE prior to 12.4-RELEASE-p7 and FreeBSD 13.2-RELEASE prior to 13.2-RELEASE-p5 the __sflush() stdio function in libc does not correctly update FILE objects' write space members for write-buffered streams when the write(2) system call returns an error. Depending on the nature of an application that calls libc's stdio functions and the presence of errors returned from the write(2) system call (or an overridden stdio write routine) a heap buffer overflow may occur. Such overflows may lead to data corruption or the execution of arbitrary code at the privilege level of the calling program.
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Analysis
by VulDB Data Team • 12/05/2023
The vulnerability described in CVE-2023-5941 affects FreeBSD operating system versions prior to specific release points, specifically impacting the standard C library implementation of stdio functions. This flaw exists within the __sflush() function which manages buffered I/O operations for write-buffered streams. The issue stems from improper handling of error conditions during file writing operations, creating a scenario where internal FILE structure state becomes inconsistent with actual system behavior. The vulnerability is classified under CWE-121 as a heap-based buffer overflow, representing a critical weakness in memory management that can be exploited by malicious actors.
The technical implementation of this vulnerability involves the interaction between the libc library's stdio subsystem and the underlying write(2) system call. When a write operation fails, the __sflush() function fails to properly update the internal write space members of FILE objects that represent buffered streams. This inconsistency occurs because the function does not account for error conditions that may alter the expected buffer state, particularly when the write(2) system call returns an error code. The flaw becomes exploitable when an application relies on libc's stdio functions and encounters write errors during buffered output operations, leading to memory corruption that can manifest as heap buffer overflows.
The operational impact of this vulnerability extends beyond simple data corruption to potentially enable arbitrary code execution within the privilege context of the calling application. Attackers can leverage this flaw by crafting specific input sequences that trigger write errors during buffered I/O operations, causing the corrupted FILE structure to be processed in ways that can be manipulated for malicious purposes. The vulnerability's exploitability depends on the application's specific usage patterns of stdio functions and the presence of error conditions that would cause write(2) to fail. This makes the vulnerability particularly dangerous in environments where applications perform extensive I/O operations and may encounter various error conditions during normal operation.
Mitigation strategies for CVE-2023-5941 focus primarily on upgrading to the patched versions of FreeBSD releases mentioned in the advisory. System administrators should prioritize updating affected systems to FreeBSD 12.4-RELEASE-p7 or 13.2-RELEASE-p5, which contain the necessary fixes for the __sflush() function's error handling. Additionally, organizations should implement monitoring for applications that perform intensive buffered I/O operations, particularly those that may encounter error conditions during write operations. The ATT&CK framework categorizes this vulnerability under T1059.007 for command and scripting interpreter execution, as exploitation may involve manipulating application behavior to trigger the vulnerable code path. Security teams should also consider implementing runtime protections and code analysis tools to detect potential exploitation attempts targeting this specific memory corruption vulnerability.