CVE-2015-5706 in Android
Summary
by MITRE
Use-after-free vulnerability in the path_openat function in fs/namei.c in the Linux kernel 3.x and 4.x before 4.0.4 allows local users to cause a denial of service or possibly have unspecified other impact via O_TMPFILE filesystem operations that leverage a duplicate cleanup operation.
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Analysis
by VulDB Data Team • 10/27/2022
The CVE-2015-5706 vulnerability represents a critical use-after-free condition within the Linux kernel's filesystem subsystem that affects kernel versions 3.x through 4.x prior to 4.0.4. This flaw exists in the path_openat function located in the fs/namei.c file, which is responsible for handling path resolution operations in the kernel's virtual filesystem layer. The vulnerability specifically manifests during O_TMPFILE filesystem operations, which are designed to create temporary files atomically without requiring a separate unlink operation. The underlying issue stems from improper handling of cleanup operations when multiple references to the same filesystem object exist simultaneously, creating a scenario where memory allocated to a structure becomes freed while still being referenced by subsequent operations.
The technical exploitation of this vulnerability requires local user privileges and leverages the specific interaction between the O_TMPFILE flag and the kernel's path resolution mechanisms. When a process creates a temporary file using O_TMPFILE and subsequently triggers a cleanup operation that duplicates or interferes with the normal reference counting behavior, the kernel's memory management system can end up freeing a structure while other code paths still maintain references to it. This use-after-free condition can result in memory corruption that manifests as system instability or potentially more severe consequences depending on the memory layout and access patterns. The vulnerability's impact extends beyond simple denial of service as the corrupted memory state could potentially enable privilege escalation or arbitrary code execution under certain conditions, though the primary documented impact remains denial of service.
The operational implications of CVE-2015-5706 are significant for any system running affected kernel versions, as local users can exploit this vulnerability to disrupt system services or potentially gain elevated privileges. The vulnerability affects systems where O_TMPFILE operations are commonly used, which includes many modern applications and system components that rely on temporary file creation for various operations. The exploitability is relatively straightforward since it only requires local user access and knowledge of the specific filesystem operations that trigger the condition. System administrators should be particularly concerned about this vulnerability in environments where users have access to shell or application interfaces that might invoke temporary file creation operations. The vulnerability's presence in both kernel 3.x and 4.x series demonstrates the persistence of this flaw across multiple kernel releases, indicating that the root cause was not adequately addressed in the codebase.
Mitigation strategies for CVE-2015-5706 should prioritize immediate kernel updates to versions 4.0.4 or later where the vulnerability has been patched. The fix implemented by the Linux kernel team addresses the race condition in the cleanup path by ensuring proper reference counting and preventing the premature freeing of structures that remain in use. Organizations should also implement monitoring for suspicious filesystem operations involving O_TMPFILE flags and consider restricting access to such operations where possible. The vulnerability aligns with CWE-416, which addresses use-after-free conditions in software systems, and could potentially map to ATT&CK technique T1068, which covers local privilege escalation through kernel vulnerabilities. Additional defensive measures include implementing proper kernel hardening configurations, enabling security modules like SELinux or AppArmor, and conducting regular vulnerability assessments to identify similar race conditions in other kernel subsystems.