CVE-2015-7872 in Linux
Summary
by MITRE
The key_gc_unused_keys function in security/keys/gc.c in the Linux kernel through 4.2.6 allows local users to cause a denial of service (OOPS) via crafted keyctl commands.
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Analysis
by VulDB Data Team • 06/23/2022
The vulnerability identified as CVE-2015-7872 represents a critical flaw in the Linux kernel's key management subsystem that enables local attackers to trigger a kernel panic or system crash through carefully crafted keyctl commands. This issue resides within the key_gc_unused_keys function located in security/keys/gc.c, which is responsible for garbage collecting unused kernel keys. The vulnerability affects Linux kernel versions through 4.2.6 and demonstrates a classic buffer over-read or improper memory handling condition that can lead to system instability and denial of service conditions.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the kernel's key garbage collection mechanism. When local users execute crafted keyctl commands, they can manipulate the key management system in such a way that the key_gc_unused_keys function processes invalid or malformed key references. This improper handling leads to kernel memory corruption and ultimately results in an OOPS condition, which is the Linux kernel's mechanism for reporting serious errors and typically results in system crash or reboot. The vulnerability specifically manifests when the kernel attempts to access memory locations that have already been freed or are otherwise invalid, creating a scenario where the kernel's memory management subsystem fails catastrophically.
From an operational perspective, this vulnerability presents significant risks for systems running affected kernel versions as it allows any local user to potentially cause a denial of service condition that could impact system availability and stability. The attack vector is particularly concerning because it requires only local access to the system, making it accessible to users with minimal privileges. In enterprise environments, this vulnerability could be exploited by malicious insiders or compromised accounts to disrupt system operations, potentially leading to service interruptions and data unavailability. The impact extends beyond simple system crashes as the OOPS condition can corrupt kernel memory structures and potentially provide opportunities for privilege escalation or further exploitation.
The vulnerability maps directly to CWE-125, which describes "Out-of-bounds Read" conditions in software systems, and aligns with ATT&CK technique T1068, which covers "Local Privilege Escalation" through kernel vulnerabilities. Organizations should implement immediate mitigations including kernel updates to versions 4.3 or later where the vulnerability has been patched, along with monitoring for suspicious keyctl command usage patterns. System administrators should also consider implementing access controls to limit local user privileges and establish robust logging mechanisms to detect potential exploitation attempts. Additionally, regular security assessments of kernel components and proactive patch management strategies are essential to prevent exploitation of similar vulnerabilities in the key management subsystem and other kernel components that may present similar attack surfaces.