CVE-2016-9755 in Linux
Summary
by MITRE
The netfilter subsystem in the Linux kernel before 4.9 mishandles IPv6 reassembly, which allows local users to cause a denial of service (integer overflow, out-of-bounds write, and GPF) or possibly have unspecified other impact via a crafted application that makes socket, connect, and writev system calls, related to net/ipv6/netfilter/nf_conntrack_reasm.c and net/ipv6/netfilter/nf_defrag_ipv6_hooks.c.
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Analysis
by VulDB Data Team • 10/12/2022
The vulnerability identified as CVE-2016-9755 resides within the Linux kernel's netfilter subsystem, specifically affecting versions prior to 4.9. This flaw manifests during IPv6 packet reassembly operations and represents a critical security issue that can be exploited by local attackers to trigger system instability or potentially achieve more severe consequences. The vulnerability impacts the core networking functionality of Linux systems and demonstrates the dangerous implications of kernel-level memory management errors in network processing components. The affected code paths are located in net/ipv6/netfilter/nf_conntrack_reasm.c and net/ipv6/netfilter/nf_defrag_ipv6_hooks.c, which handle connection tracking and IPv6 defragmentation respectively.
The technical root cause of this vulnerability involves an integer overflow condition that occurs during IPv6 reassembly operations within the netfilter framework. When processing crafted IPv6 packets, the kernel fails to properly validate integer values used in memory allocation calculations, leading to an integer overflow that subsequently causes an out-of-bounds write condition. This memory corruption can result in a general protection fault (GPF) that crashes the kernel and brings the entire system to a halt. The vulnerability is particularly dangerous because it requires only local user privileges to exploit, making it accessible to any user account on the system. The flaw stems from inadequate input validation and memory boundary checking during the packet reassembly process, where the kernel does not properly sanitize the length parameters of fragmented IPv6 packets before performing memory operations.
The operational impact of CVE-2016-9755 extends beyond simple denial of service to potentially enable more sophisticated attacks. While the primary effect is a system crash leading to denial of service, the out-of-bounds write condition could theoretically be leveraged to execute arbitrary code if properly exploited, though this would require additional attack vectors. The vulnerability affects all Linux systems running kernel versions before 4.9, making it particularly concerning for enterprise environments where kernel updates may be delayed or where legacy systems are maintained. Network services that rely heavily on IPv6 connectivity become particularly vulnerable, as attackers can craft malicious packets to trigger the vulnerability. The low privilege requirement means that even unprivileged users can cause system-wide disruptions, making this a significant concern for multi-user systems and cloud environments where isolation between user accounts is paramount.
Mitigation strategies for CVE-2016-9755 primarily focus on kernel version upgrades to 4.9 or later, which contain the necessary patches to address the integer overflow and memory corruption issues. System administrators should prioritize updating their kernel versions as a critical security measure, particularly in environments where local privilege escalation risks are high. Additionally, network administrators can implement firewall rules to limit IPv6 traffic or disable IPv6 functionality on systems where it is not required, though this approach may not be practical in IPv6-enabled environments. The vulnerability aligns with CWE-190, Integer Overflow or Wraparound, and CWE-787, Out-of-bounds Write, demonstrating how integer arithmetic errors can cascade into memory corruption vulnerabilities. From an ATT&CK framework perspective, this vulnerability maps to T1068, Exploitation for Privilege Escalation, and T1499, Endpoint Detection and Response Evasion, as it can be used to disrupt system operations and potentially enable further attack vectors. Organizations should also implement monitoring solutions to detect unusual network traffic patterns that might indicate exploitation attempts, and maintain regular patch management processes to ensure timely remediation of such kernel-level vulnerabilities.