CVE-2016-3672 in Android
Summary
by MITRE
The arch_pick_mmap_layout function in arch/x86/mm/mmap.c in the Linux kernel through 4.5.2 does not properly randomize the legacy base address, which makes it easier for local users to defeat the intended restrictions on the ADDR_NO_RANDOMIZE flag, and bypass the ASLR protection mechanism for a setuid or setgid program, by disabling stack-consumption resource limits.
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Analysis
by VulDB Data Team • 12/09/2024
The vulnerability described in CVE-2016-3672 resides within the Linux kernel's memory management subsystem, specifically in the arch/x86/mm/mmap.c file. This flaw affects kernel versions through 4.5.2 and represents a significant weakness in the address space layout randomization mechanism that is fundamental to modern operating system security. The issue stems from the arch_pick_mmap_layout function which is responsible for determining memory layout during process execution, particularly when the ADDR_NO_RANDOMIZE flag is in effect. This function fails to properly randomize the legacy base address, creating predictable memory layout patterns that adversaries can exploit to bypass security protections.
The technical nature of this vulnerability involves the improper implementation of address space layout randomization within the Linux kernel's memory management framework. When the ADDR_NO_RANDOMIZE flag is disabled, the kernel should still maintain sufficient entropy in memory layout to prevent attackers from easily predicting memory addresses. However, the flaw in arch_pick_mmap_layout allows for insufficient randomization of the legacy base address, which means that when stack-consumption resource limits are disabled, attackers can more easily determine the memory layout of setuid or setgid programs. This represents a direct violation of the principle of least privilege and undermines the fundamental security assumptions that ASLR relies upon. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited by local users without requiring network access or special privileges beyond normal user accounts.
The operational impact of this vulnerability is substantial for systems running affected kernel versions, as it directly enables local privilege escalation attacks that can bypass critical security mechanisms. When combined with the ability to disable stack-consumption resource limits, attackers can effectively defeat ASLR protections for setuid and setgid programs, which are designed to provide elevated privileges while maintaining security boundaries. This weakness allows malicious users to predict memory addresses and potentially execute return-oriented programming attacks or other exploitation techniques that rely on knowing the memory layout. The vulnerability particularly affects systems where setuid/setgid binaries are present, as these programs are often targets for privilege escalation attacks due to their elevated privileges. This flaw essentially creates a backdoor that allows attackers to circumvent the security protections that should prevent local users from gaining elevated privileges through memory layout prediction.
Mitigation strategies for CVE-2016-3672 primarily focus on kernel updates and system hardening measures. The most effective solution involves upgrading to a patched kernel version that properly implements the arch_pick_mmap_layout function with adequate randomization of legacy base addresses. System administrators should prioritize applying security patches as soon as they become available, as this vulnerability can be exploited by local users to gain elevated privileges. Additional mitigations include implementing strict resource limits on stack consumption, monitoring for unusual memory access patterns, and employing additional security controls such as grsecurity or PaX patches that provide enhanced memory protection mechanisms. Organizations should also conduct regular security assessments to identify systems running vulnerable kernel versions and ensure proper patch management procedures are in place to prevent exploitation. The vulnerability aligns with CWE-699 (Weaknesses in the Design of System Security) and represents a specific implementation flaw that can be categorized under ATT&CK technique T1068 (Local Privilege Escalation) through improper use of system resources to bypass security controls.