CVE-2018-12233 in Linux
Summary
by MITRE
In the ea_get function in fs/jfs/xattr.c in the Linux kernel through 4.17.1, a memory corruption bug in JFS can be triggered by calling setxattr twice with two different extended attribute names on the same file. This vulnerability can be triggered by an unprivileged user with the ability to create files and execute programs. A kmalloc call is incorrect, leading to slab-out-of-bounds in jfs_xattr.
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Analysis
by VulDB Data Team • 03/22/2023
The vulnerability identified as CVE-2018-12233 represents a critical memory corruption issue within the Linux kernel's JFS (Journaled File System) implementation. This flaw exists in the ea_get function located in fs/jfs/xattr.c and affects Linux kernel versions through 4.17.1, making it a widespread concern across numerous system deployments. The vulnerability stems from improper handling of extended attributes during concurrent operations, specifically when setxattr is invoked twice with different attribute names on the same file. The flaw manifests as an incorrect kmalloc call that results in slab-out-of-bounds memory access patterns, creating potential for arbitrary code execution or system instability.
The technical implementation of this vulnerability involves a race condition within the extended attribute management subsystem of JFS. When an unprivileged user executes the specific sequence of operations, the kernel's memory allocator fails to properly manage the slab allocation for extended attribute storage. The kmalloc call in question does not account for proper bounds checking when allocating memory for attribute storage structures, leading to memory corruption that can overwrite adjacent memory regions within the kernel's slab allocator. This type of vulnerability aligns with CWE-122, which specifically addresses heap-based buffer overflow conditions, and represents a classic case of improper memory management in kernel space operations.
The operational impact of CVE-2018-12233 extends beyond simple system instability, as it creates potential attack vectors for privilege escalation and system compromise. An unprivileged user with basic file creation and execution capabilities can exploit this vulnerability to corrupt kernel memory structures, potentially leading to denial of service conditions or more severe consequences including arbitrary code execution. The vulnerability's accessibility through standard user-level operations makes it particularly dangerous in multi-user environments where users may not have elevated privileges but can still influence kernel memory management through carefully crafted extended attribute operations. This aligns with ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation' through kernel vulnerabilities.
Mitigation strategies for this vulnerability require immediate kernel updates to versions that contain the patched implementation of the ea_get function in JFS. System administrators should prioritize applying security patches that correct the kmalloc allocation logic and implement proper bounds checking for extended attribute operations. Additionally, monitoring for unusual extended attribute operations and implementing proper access controls can help detect potential exploitation attempts. The vulnerability demonstrates the critical importance of proper memory management in kernel space implementations and highlights the need for comprehensive testing of concurrent access patterns in file system operations. Organizations should also consider implementing kernel hardening measures such as stack canaries and memory protection mechanisms to reduce the impact of similar vulnerabilities in the future.