CVE-2019-3896 in Linux
Summary
by MITRE
A double-free can happen in idr_remove_all() in lib/idr.c in the Linux kernel 2.6 branch. An unprivileged local attacker can use this flaw for a privilege escalation or for a system crash and a denial of service (DoS).
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Analysis
by VulDB Data Team • 10/06/2023
The vulnerability identified as CVE-2019-3896 represents a critical double-free error within the Linux kernel's internal data structure management system. This flaw exists in the idr_remove_all() function located in lib/idr.c within the 2.6 kernel branch, making it particularly concerning as it affects a foundational component of the operating system's memory management infrastructure. The issue stems from improper handling of reference counting mechanisms when removing all entries from an IDR (Integer Dense Range) structure, which is a core data structure used throughout the kernel for managing various resources including file descriptors, network connections, and other system objects. The vulnerability classifies under CWE-415 as a double free condition, where the same memory block is freed twice, potentially leading to memory corruption and arbitrary code execution.
The operational impact of this vulnerability extends beyond simple system instability, as it provides an unprivileged local attacker with a pathway for privilege escalation. When an attacker can manipulate the IDR data structure to trigger the double-free condition, they can potentially overwrite critical kernel memory locations with controlled data, enabling them to execute arbitrary code with kernel-level privileges. This represents a significant escalation from a simple denial of service scenario to a full system compromise. The vulnerability is particularly dangerous because it requires no special privileges to exploit, making it accessible to any user account on the system. The attack vector involves careful manipulation of the IDR subsystem through legitimate kernel interfaces, exploiting the lack of proper bounds checking and reference counting validation in the idr_remove_all() function. This flaw can be triggered through various kernel APIs that utilize IDR structures, including but not limited to device management interfaces and system call handlers that maintain reference counts for kernel objects.
The exploitation of this vulnerability demonstrates the classic ATT&CK technique of privilege escalation through kernel memory corruption, specifically leveraging the T1068 technique of "Local Privilege Escalation" by corrupting kernel data structures. The double-free condition creates a memory layout that allows attackers to manipulate kernel memory in ways that can be used to gain root privileges or cause system crashes. Mitigation strategies include applying the official kernel patches released by the Linux kernel security team, which address the specific reference counting logic in the idr_remove_all() function. System administrators should prioritize updating affected kernel versions, particularly those in the 2.6 branch, as this version series is no longer actively maintained and contains multiple known vulnerabilities. Additionally, implementing kernel hardening measures such as stack canaries, kernel address space layout randomization, and control flow integrity checks can provide additional defense in depth. The vulnerability also highlights the importance of proper memory management practices in kernel code, specifically the need for robust reference counting mechanisms and proper validation of data structure integrity before memory deallocation operations. Organizations should conduct thorough vulnerability assessments to identify systems running affected kernel versions and ensure that all kernel components are updated to versions that contain the necessary fixes for this and related memory corruption vulnerabilities.