CVE-2011-1171 in Linux
Summary
by MITRE
net/ipv4/netfilter/ip_tables.c in the IPv4 implementation in the Linux kernel before 2.6.39 does not place the expected \0 character at the end of string data in the values of certain structure members, which allows local users to obtain potentially sensitive information from kernel memory by leveraging the CAP_NET_ADMIN capability to issue a crafted request, and then reading the argument to the resulting modprobe process.
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Analysis
by VulDB Data Team • 11/13/2021
The vulnerability identified as CVE-2011-1171 represents a classic kernel memory disclosure flaw within the Linux kernel's netfilter framework, specifically affecting the ip_tables subsystem. This issue resides in the net/ipv4/netfilter/ip_tables.c file and impacts Linux kernel versions prior to 2.6.39, creating a significant security risk for systems that utilize iptables for packet filtering and network address translation. The flaw manifests as a buffer overread condition where the kernel fails to properly null-terminate string data within certain structure members, allowing for information leakage from kernel memory space.
The technical mechanism behind this vulnerability involves the improper handling of string data within kernel structures when processing netfilter operations. When a local user with CAP_NET_ADMIN capability issues a crafted iptables request, the kernel processes this input through the netfilter subsystem without properly terminating string values in structure members. This oversight creates a situation where adjacent kernel memory contents are exposed when the system subsequently passes arguments to the modprobe process, which is typically invoked during network operations to load kernel modules. The vulnerability specifically affects how the kernel handles string data in structure members related to iptables rule processing, where the missing null terminator allows for memory contents to be read beyond the intended boundaries.
From an operational perspective, this vulnerability creates a serious information disclosure risk that can expose sensitive kernel memory contents to local attackers. The requirement for CAP_NET_ADMIN capability means that the attack vector is limited to users who already possess significant network administration privileges, but this still represents a privilege escalation concern within the kernel space. The exposure of kernel memory can potentially reveal sensitive information including cryptographic keys, passwords, system configuration data, or other confidential information stored in kernel memory regions. This information leakage can be particularly dangerous in multi-tenant environments or systems where different users share the same host, as it provides attackers with additional attack surface and potential credential information that could be leveraged for further exploitation.
The security implications of this vulnerability extend beyond simple information disclosure, as the leaked memory contents could contain critical system information that aids in developing more sophisticated attacks. Attackers could potentially use the leaked data to identify system configurations, memory layouts, or other sensitive information that would otherwise remain hidden from local users. This vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and represents a specific instance where improper string handling in kernel space creates a memory exposure. The attack requires a user to have the capability to modify netfilter rules, which is typically restricted to privileged users but still represents a significant risk when combined with other potential vulnerabilities or when the system is compromised through other attack vectors.
Mitigation strategies for CVE-2011-1171 focus primarily on upgrading to Linux kernel versions 2.6.39 or later where the vulnerability has been addressed through proper string termination in kernel structures. System administrators should also implement proper privilege controls to limit access to CAP_NET_ADMIN capabilities, ensuring that only trusted users have the ability to modify network filtering rules. Additionally, monitoring for unusual iptables rule modifications and modprobe process invocations can help detect potential exploitation attempts. The fix implemented in kernel 2.6.39 specifically addresses the string termination issue in the ip_tables.c file, ensuring that all string data within structure members is properly null-terminated before being processed or passed to user-space applications. This remediation follows established security practices for preventing information disclosure vulnerabilities and aligns with the broader ATT&CK framework's approach to defending against kernel-level information disclosure attacks through proper memory management and input validation.