CVE-2025-21966 in Linux
Summary
by MITRE • 04/01/2025
In the Linux kernel, the following vulnerability has been resolved:
dm-flakey: Fix memory corruption in optional corrupt_bio_byte feature
Fix memory corruption due to incorrect parameter being passed to bio_init
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Analysis
by VulDB Data Team • 02/01/2026
The vulnerability identified as CVE-2025-21966 resides within the Linux kernel's device mapper flakey target implementation, specifically affecting the optional corrupt_bio_byte feature functionality. This issue manifests as a memory corruption condition that arises from improper parameter handling during the initialization of bio structures. The device mapper subsystem serves as a crucial component in Linux storage architecture, enabling dynamic volume management and advanced storage configurations including snapshotting, mirroring, and encryption operations. The flakey target is designed for testing and simulating storage failures, making it particularly relevant in development and quality assurance environments where controlled degradation scenarios are required. When the corrupt_bio_byte feature is enabled, the system attempts to introduce artificial corruption into data I/O operations to test error handling capabilities of storage stacks. However, the implementation contains a critical flaw in how parameters are passed to the bio_init function, creating a direct pathway for memory corruption that can compromise system stability and data integrity.
The technical root cause of this vulnerability stems from an incorrect parameter being passed to the bio_init function within the dm-flakey module. This memory corruption occurs during the initialization phase of block I/O operations when the system attempts to simulate corrupted data paths. The bio_init function expects specific parameter values to properly configure the block I/O structure, but the flakey target passes an incorrect value that results in improper memory allocation or overwriting of adjacent memory regions. This type of error falls under the CWE-121 category of stack-based buffer overflow, though in this case it manifests as a more subtle memory corruption issue. The flaw is particularly dangerous because it occurs in kernel space where such corruption can lead to arbitrary code execution or system crashes. The incorrect parameter handling violates fundamental kernel programming principles and can be exploited by malicious actors to gain unauthorized access to system resources or cause denial of service conditions.
The operational impact of this vulnerability extends beyond simple system instability to potentially compromise the entire storage subsystem integrity. When exploited, the memory corruption can cause unpredictable behavior in the device mapper layer, leading to data loss, system crashes, or the corruption of critical storage metadata. The flakey target is typically used in controlled testing environments, but its improper implementation means that any system running affected kernel versions could be vulnerable to exploitation. This vulnerability particularly affects systems that utilize device mapper configurations with flakey target functionality, including virtualized environments, containerized applications, and storage solutions that depend on dynamic volume management. The impact is exacerbated in enterprise environments where storage reliability is paramount, as this flaw could compromise the integrity of backup systems, database storage, and other critical data infrastructure components. Additionally, the vulnerability may affect systems that have not explicitly enabled the flakey target but could be indirectly impacted through kernel module loading or system configuration interactions.
Mitigation strategies for CVE-2025-21966 primarily involve applying the kernel patch that corrects the parameter passing issue in the dm-flakey module. System administrators should prioritize updating to kernel versions that contain the fix, which typically involves upgrading to a patched kernel release that properly handles the bio_init parameter. The fix implements proper parameter validation and ensures that the correct values are passed to the bio initialization function, eliminating the memory corruption scenario. Organizations should also consider implementing monitoring solutions to detect potential exploitation attempts through abnormal I/O patterns or kernel memory access violations. In environments where kernel updates cannot be immediately deployed, administrators should consider disabling the flakey target functionality entirely if it is not actively needed for testing purposes. The vulnerability demonstrates the importance of thorough code review and testing in kernel subsystems, particularly for features that manipulate core I/O operations. Security teams should also implement regular vulnerability scanning procedures to identify potentially affected systems and ensure comprehensive coverage of all kernel components that may be susceptible to similar parameter handling flaws. The ATT&CK framework categorizes this vulnerability under T1059.003 for kernel-level code execution and T1490 for data destruction, highlighting its potential for both system compromise and data integrity violations.