CVE-2024-38587 in Linux
Summary
by MITRE • 06/19/2024
In the Linux kernel, the following vulnerability has been resolved:
speakup: Fix sizeof() vs ARRAY_SIZE() bug
The "buf" pointer is an array of u16 values. This code should be using ARRAY_SIZE() (which is 256) instead of sizeof() (which is 512), otherwise it can the still got out of bounds.
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Analysis
by VulDB Data Team • 10/04/2025
The vulnerability identified as CVE-2024-38587 resides within the Linux kernel's speakup subsystem, which is responsible for speech synthesis and text-to-speech functionality for visually impaired users. This subsystem provides accessibility features that convert text output from the system into audible speech, making computer interfaces more accessible to users with visual impairments. The flaw manifests in how the code handles memory buffer sizing calculations, specifically within the array management logic that governs how speech data is processed and transmitted to audio devices.
The technical root cause involves a fundamental misunderstanding in memory management calculations where the code incorrectly uses sizeof() instead of ARRAY_SIZE() when determining buffer boundaries. The affected buffer named "buf" is defined as an array of u16 values, which means each element occupies two bytes of memory. When sizeof() is applied to the array, it returns the total byte size of the entire array, which in this case would be 512 bytes for 256 elements. However, the code should be using ARRAY_SIZE() which correctly returns the count of elements in the array, which is 256. This discrepancy creates a buffer overflow scenario where the code attempts to access memory beyond the intended array boundaries, potentially leading to memory corruption or arbitrary code execution.
The operational impact of this vulnerability extends beyond simple memory corruption, as it represents a classic buffer overflow condition that could be exploited by malicious actors to gain unauthorized access to system resources. The vulnerability specifically affects the speakup subsystem's ability to process speech data correctly, potentially allowing attackers to manipulate how text is converted to speech or to execute malicious code within the kernel context. This type of vulnerability is particularly concerning in kernel space where privilege escalation is possible, as it could allow attackers to bypass security controls and gain elevated system privileges. The flaw aligns with CWE-121, which describes stack-based buffer overflow conditions, and could potentially map to ATT&CK technique T1068, which involves exploiting legitimate credentials or privileges to execute malicious code.
The fix implemented addresses this by correcting the memory calculation to properly use ARRAY_SIZE() instead of sizeof(), ensuring that the code correctly references the number of array elements rather than the total memory footprint. This correction prevents the out-of-bounds memory access that could occur when the code attempts to process speech data beyond the intended buffer limits. System administrators should prioritize applying this patch as it resolves a critical memory safety issue within the kernel's accessibility subsystem, particularly important for systems serving users who rely on assistive technologies. The vulnerability demonstrates the importance of careful memory management in kernel code and highlights how seemingly minor calculation errors can create significant security risks in operating system components that handle user input and system output processing.