CVE-2019-9213 in Linux
Summary
by MITRE
In the Linux kernel before 4.20.14, expand_downwards in mm/mmap.c lacks a check for the mmap minimum address, which makes it easier for attackers to exploit kernel NULL pointer dereferences on non-SMAP platforms. This is related to a capability check for the wrong task.
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Analysis
by VulDB Data Team • 12/22/2024
The vulnerability identified as CVE-2019-9213 represents a critical flaw in the Linux kernel's memory management subsystem that specifically affects versions prior to 4.20.14. This issue resides within the expand_downwards function located in the mm/mmap.c file, which handles memory mapping operations in the kernel space. The vulnerability stems from an inadequate validation mechanism that fails to properly enforce the mmap minimum address restriction, creating a potential pathway for malicious exploitation. The flaw is particularly concerning because it weakens the kernel's defenses against NULL pointer dereference attacks, which can lead to system instability and potential privilege escalation.
The technical implementation of this vulnerability demonstrates a fundamental oversight in the kernel's capability checking mechanism. The expand_downwards function does not properly validate whether the current task has sufficient privileges to perform memory mapping operations at the specified address range. This misconfiguration creates a scenario where attackers can manipulate memory allocation patterns to bypass intended security controls. The vulnerability is specifically amplified on non-SMAP (Supervisor Mode Access Prevention) platforms, where the lack of hardware-based memory protection mechanisms makes the kernel's software safeguards even more critical. This flaw represents a classic case of improper access control where the kernel fails to validate the correct task context before permitting memory mapping operations.
The operational impact of CVE-2019-9213 extends beyond simple memory management issues, as it creates opportunities for attackers to exploit kernel vulnerabilities through carefully crafted memory mapping sequences. When combined with other kernel flaws, this vulnerability can potentially allow attackers to execute arbitrary code with kernel privileges, leading to complete system compromise. The weakness in the mmap minimum address check means that malicious processes can attempt to map memory regions that should be restricted, potentially enabling techniques such as kernel address space layout randomization (ASLR) bypasses or privilege escalation attacks. The vulnerability's exploitation requires careful targeting of non-SMAP platforms, but the potential consequences remain severe enough to warrant immediate attention.
Security mitigations for CVE-2019-9213 primarily focus on updating to kernel versions 4.20.14 or later, where the proper mmap minimum address validation has been implemented. System administrators should prioritize patching affected systems, particularly those running on non-SMAP hardware platforms where the vulnerability is most exploitable. Additional defensive measures include implementing proper kernel lockdown mechanisms, enabling kernel address space layout randomization, and monitoring for suspicious memory mapping patterns. Organizations should also consider implementing runtime protection solutions that can detect and prevent exploitation attempts targeting this specific vulnerability. The fix addresses the core issue by ensuring that the expand_downwards function properly validates the minimum address requirements before allowing memory mapping operations, thereby preventing attackers from exploiting the capability check for the wrong task scenario. This vulnerability aligns with CWE-284 Access Control Issues and can be mapped to ATT&CK techniques involving privilege escalation and kernel exploitation.