CVE-2017-5546 in Linux
Summary
by MITRE
The freelist-randomization feature in mm/slab.c in the Linux kernel 4.8.x and 4.9.x before 4.9.5 allows local users to cause a denial of service (duplicate freelist entries and system crash) or possibly have unspecified other impact in opportunistic circumstances by leveraging the selection of a large value for a random number.
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Analysis
by VulDB Data Team • 11/11/2022
The vulnerability identified as CVE-2017-5546 resides within the Linux kernel's memory management subsystem, specifically in the slab allocator implementation located in mm/slab.c. This flaw affects kernel versions 4.8.x and 4.9.x prior to 4.9.5 and represents a critical security issue that can be exploited through the freelist-randomization feature designed to prevent certain types of memory corruption attacks. The vulnerability stems from improper handling of random number selection during slab allocation processes, creating conditions where malicious actors can manipulate the system's memory management behavior.
The technical root cause of this vulnerability lies in the slab allocator's attempt to randomize free list entries to prevent cache timing attacks and other memory-based exploitation techniques. When a large random number is selected during the freelist randomization process, the algorithm fails to properly validate or constrain the generated values, leading to potential duplicate entries within the freelist structure. This condition creates a cascade of issues where the memory allocator's internal data structures become corrupted, potentially causing kernel panics and system crashes. The flaw operates at the kernel level, making it particularly dangerous as it can be triggered by local users without requiring elevated privileges, though it may also present opportunities for more sophisticated exploitation under specific circumstances.
The operational impact of CVE-2017-5546 manifests primarily as denial of service conditions where system stability is compromised through kernel crashes and potential system hangs. However, the vulnerability's implications extend beyond simple service disruption as the opportunistic nature of the flaw suggests potential for more severe consequences including information disclosure or privilege escalation under certain conditions. Attackers can leverage this vulnerability to repeatedly trigger system instability, effectively creating a persistent denial of service condition that can be difficult to detect and mitigate. The vulnerability operates through the kernel's memory management subsystem, making it particularly challenging to defend against since it resides in the core operating system components that handle all memory allocation requests.
Security professionals should consider this vulnerability in the context of CWE-129, which addresses improper validation of the length/size of a buffer, and potentially CWE-362, which deals with concurrent execution using shared data structures. The attack pattern aligns with techniques described in the ATT&CK framework under T1059 for system execution and T1499 for endpoint denial of service. Organizations should prioritize immediate patching of affected kernel versions to address this vulnerability, as the exploitation can occur through local user access without requiring network connectivity or specialized privileges. The mitigation strategy should include comprehensive kernel updates, implementation of kernel lockdown mechanisms, and monitoring for unusual system behavior that might indicate exploitation attempts, particularly in environments where local user access is not strictly controlled.