CVE-2019-9162 in Linux
Summary
by MITRE
In the Linux kernel before 4.20.12, net/ipv4/netfilter/nf_nat_snmp_basic_main.c in the SNMP NAT module has insufficient ASN.1 length checks (aka an array index error), making out-of-bounds read and write operations possible, leading to an OOPS or local privilege escalation. This affects snmp_version and snmp_helper.
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Analysis
by VulDB Data Team • 12/22/2024
The vulnerability identified as CVE-2019-9162 represents a critical flaw in the Linux kernel's SNMP NAT module that emerged prior to version 4.20.12. This issue resides within the file net/ipv4/netfilter/nf_nat_snmp_basic_main.c and specifically targets the ASN.1 length validation mechanisms that are fundamental to proper network protocol handling. The flaw manifests as inadequate bounds checking during ASN.1 parsing operations, creating a condition where array index calculations can exceed valid memory boundaries. This fundamental deficiency in input validation creates a pathway for malicious actors to exploit the kernel's network filtering capabilities through crafted SNMP packets that manipulate the NAT module's internal state.
The technical implementation of this vulnerability stems from insufficient validation of ASN.1 encoded data structures within the SNMP NAT processing pipeline. When the kernel receives SNMP packets that contain malformed ASN.1 length fields, the parsing logic fails to properly validate the boundaries of array operations, leading to potential out-of-bounds memory access patterns. This condition creates two primary attack vectors: the possibility of read operations that access memory locations beyond allocated buffers, and write operations that can overwrite adjacent memory regions. The vulnerability specifically impacts the snmp_version and snmp_helper components of the NAT module, which are responsible for maintaining state information about SNMP traffic passing through the network filter. The lack of proper bounds checking in these critical processing paths allows attackers to manipulate kernel memory structures through carefully crafted network traffic.
The operational impact of CVE-2019-9162 extends beyond simple denial of service conditions to encompass potential local privilege escalation capabilities. An attacker who successfully exploits this vulnerability can achieve kernel-level code execution, effectively gaining root privileges on the affected system. The out-of-bounds read operations can expose sensitive kernel memory contents, potentially revealing information about kernel structures, memory layouts, or security credentials. More critically, the write operations can corrupt kernel data structures, leading to system instability or complete system compromise. The vulnerability affects systems running Linux kernel versions prior to 4.20.12, making it particularly concerning for organizations maintaining older kernel versions in production environments. The attack surface is broad as the vulnerability can be triggered through normal network traffic processing, requiring minimal privileges to exploit and potentially allowing for remote code execution in network-facing systems.
Mitigation strategies for CVE-2019-9162 primarily focus on kernel version updates and immediate system patching. Organizations should prioritize upgrading to Linux kernel version 4.20.12 or later, which contains the necessary fixes for the ASN.1 length validation issues. System administrators should also implement network segmentation and firewall rules to limit exposure of affected systems to untrusted network traffic. The vulnerability aligns with CWE-129, which addresses insufficient validation of length of input buffers, and corresponds to ATT&CK technique T1068, which involves exploiting local privileges to gain elevated access. Additional defensive measures include enabling kernel hardening features such as stack canaries, address space layout randomization, and kernel module signing to prevent exploitation of similar vulnerabilities. Monitoring network traffic for anomalous SNMP patterns and implementing intrusion detection systems can help identify potential exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation in kernel space operations, where insufficient bounds checking can lead to catastrophic system compromise and highlights the necessity of maintaining up-to-date security patches across all system components.