CVE-2016-4805 in Android
Summary
by MITRE • 01/25/2023
Use-after-free vulnerability in drivers/net/ppp/ppp_generic.c in the Linux kernel before 4.5.2 allows local users to cause a denial of service (memory corruption and system crash, or spinlock) or possibly have unspecified other impact by removing a network namespace, related to the ppp_register_net_channel and ppp_unregister_channel functions.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability identified as CVE-2016-4805 represents a critical use-after-free condition within the Linux kernel's Point-to-Point Protocol (PPP) implementation, specifically in the ppp_generic.c driver file. This flaw exists in kernel versions prior to 4.5.2 and demonstrates a fundamental memory management error that can be exploited by local attackers to compromise system stability. The vulnerability manifests when network namespaces are manipulated through the ppp_register_net_channel and ppp_unregister_channel functions, creating a scenario where freed memory locations are accessed after being deallocated, leading to unpredictable behavior and potential system compromise.
The technical nature of this vulnerability aligns with CWE-416, which categorizes use-after-free conditions as a critical memory safety issue. The flaw occurs when the PPP subsystem fails to properly manage reference counts and memory pointers during network namespace operations, particularly when transitioning between different network contexts. When a network namespace is removed, the ppp_unregister_channel function attempts to clean up resources while the ppp_register_net_channel function may still hold references to the same memory structures, creating a race condition that results in the premature deallocation of memory that subsequent operations attempt to access. This memory corruption scenario can trigger kernel oops messages, system crashes, or more insidiously, allow for privilege escalation or persistent system instability.
The operational impact of CVE-2016-4805 extends beyond simple denial of service, as local attackers with basic system access can leverage this vulnerability to cause system-wide disruptions or potentially escalate privileges. The vulnerability's exploitation can result in immediate system crashes, forcing administrators to reboot systems and potentially leading to data loss or service interruptions in production environments. From an adversarial perspective, this vulnerability maps to ATT&CK technique T1068, which involves exploiting local privileges to gain elevated access, and T1499, which encompasses system disruption through resource exhaustion or memory corruption. The vulnerability particularly affects systems running kernel versions before 4.5.2 where PPP is actively used for network connectivity, including virtual private networks, dial-up connections, and various network virtualization scenarios.
Mitigation strategies for this vulnerability require immediate kernel version updates to 4.5.2 or later, where the memory management issues have been addressed through proper reference counting and resource cleanup mechanisms. System administrators should also implement network namespace monitoring to detect anomalous PPP channel operations and consider disabling unnecessary PPP functionality on systems where it is not required. The fix implemented in the patched kernel versions addresses the root cause by ensuring proper synchronization between channel registration and unregistration operations, preventing the premature deallocation of memory structures that are still in use. Organizations should also conduct comprehensive vulnerability assessments to identify systems running vulnerable kernel versions and establish patch management processes that prioritize kernel updates, particularly in environments where local privilege escalation risks are significant. The vulnerability serves as a reminder of the critical importance of memory safety in kernel-level code and the potential for seemingly benign network operations to create severe security implications when proper resource management is not implemented.