CVE-2026-72181 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
mips: sched: Fix CPUMASK_OFFSTACK memory corruption
This patch addresses a critical memory management flaw. When CONFIG_CPUMASK_OFFSTACK is enabled, cpumask_var_t is a pointer. Consequently, sizeof(new_mask) evaluates to the pointer size, causing copy_from_user() to clobber the mask pointer. Furthermore, the old logic performed copy_from_user() before allocating the mask.
Fix this by allocating new_mask first. To handle variable-sized user masks correctly, use cpumask_size() to truncate overly large user masks or pad undersized masks with zeros before copying the data directly into the allocated buffer.
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability resides in the mips architecture implementation of the Linux kernel's scheduler subsystem where a critical memory corruption issue occurs when the CONFIG_CPUMASK_OFFSTACK configuration option is enabled. The flaw manifests in how cpumask_var_t variables are handled during memory operations, creating a dangerous race condition between memory allocation and data copying processes.
The technical root cause involves the improper sequence of operations within the cpumask handling logic where copy_from_user() is executed before allocating sufficient memory for the mask variable. When CONFIG_CPUMASK_OFFSTACK is active, cpumask_var_t is defined as a pointer type rather than a fixed-size array, which means that sizeof(new_mask) returns the pointer size rather than the intended mask size. This fundamental mismatch causes copy_from_user() to overwrite the pointer value itself rather than the memory it points to, leading to immediate memory corruption and potential system instability.
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 or cause system crashes. The flaw affects systems running Linux kernels with MIPS architecture and the specific configuration flag enabled, potentially compromising the integrity of the scheduler's CPU mask management functionality. This type of memory corruption vulnerability aligns with CWE-121 and CWE-787 categories related to buffer overflow conditions and improper lifetime management.
The patch implementation addresses this by reordering the operations to allocate memory for new_mask before performing any data copying operations, ensuring that sufficient space exists for the user-provided mask data. Additionally, the fix incorporates proper size handling through cpumask_size() function calls that either truncate excessively large user masks or pad smaller masks with zeros to maintain data integrity during the copy operation. This approach follows established security practices for preventing memory corruption vulnerabilities and aligns with ATT&CK techniques related to privilege escalation and system compromise.
The mitigation strategy involves ensuring that all systems using MIPS-based Linux kernels with CONFIG_CPUMASK_OFFSTACK enabled receive the patched kernel updates, while also implementing proper configuration management to prevent unintended enabling of problematic kernel features. Organizations should conduct thorough testing of kernel patches in production environments to verify that the fix does not introduce regressions in scheduler functionality or system performance metrics.