CVE-2011-1080 in Linux
Summary
by MITRE
The do_replace function in net/bridge/netfilter/ebtables.c in the Linux kernel before 2.6.39 does not ensure that a certain name field ends with a \0 character, which allows local users to obtain potentially sensitive information from kernel stack memory by leveraging the CAP_NET_ADMIN capability to replace a table, and then reading a modprobe command line.
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Analysis
by VulDB Data Team • 12/05/2021
The vulnerability identified as CVE-2011-1080 resides within the Linux kernel's netfilter framework, specifically in the ebtables component responsible for Ethernet bridge packet filtering. This flaw exists in kernel versions prior to 2.6.39 and represents a classic case of improper string termination that can lead to information disclosure. The vulnerability is particularly concerning because it requires only the CAP_NET_ADMIN capability, which is commonly granted to network administrators and can be exploited by local users with minimal privileges. The affected function do_replace in net/bridge/netfilter/ebtables.c fails to properly null-terminate a name field during table replacement operations, creating a condition where kernel memory contents may be inadvertently exposed.
The technical exploitation of this vulnerability occurs through a specific sequence of operations that leverages the kernel's ebtables subsystem. When a local user with CAP_NET_ADMIN capability performs a table replacement operation, the do_replace function processes the table name without ensuring proper null termination of the name field. This memory management flaw allows subsequent operations to read beyond the intended boundaries of the allocated buffer, potentially accessing adjacent kernel stack memory regions. The sensitive information obtained through this technique could include kernel pointers, stack canaries, or other confidential data that should remain protected from user-space access. This type of information disclosure vulnerability is classified under CWE-126 as "Buffer Over-read" and represents a memory safety issue that can be exploited to gain insights into kernel memory layout and potentially aid in more sophisticated attacks.
The operational impact of CVE-2011-1080 extends beyond simple information disclosure, as it creates a potential avenue for privilege escalation and system compromise. While the vulnerability itself does not directly provide code execution capabilities, the exposure of kernel memory contents can be leveraged by attackers to understand system internals and potentially identify additional vulnerabilities. The fact that exploitation requires only CAP_NET_ADMIN capability means that this vulnerability is accessible to users who typically have legitimate network administration privileges, making it particularly dangerous in environments where such capabilities are widely distributed. Attackers could use the leaked information to bypass security mechanisms such as kernel address space layout randomization or to craft more targeted attacks against other kernel vulnerabilities. This vulnerability aligns with ATT&CK technique T1068 which involves exploiting vulnerabilities in the kernel or operating system to escalate privileges or gain unauthorized access.
Mitigation strategies for CVE-2011-1080 focus primarily on upgrading to kernel versions 2.6.39 or later where the vulnerability has been addressed through proper null termination of the name field in the do_replace function. System administrators should prioritize kernel updates as a critical security measure, particularly in environments where users possess CAP_NET_ADMIN capabilities. Additionally, implementing least privilege principles and restricting unnecessary network administration privileges can significantly reduce the attack surface for this vulnerability. The fix implemented in the patched kernel versions ensures that all name fields are properly null-terminated before processing, preventing the over-read condition that enabled information disclosure. Organizations should also consider monitoring for unauthorized table replacement operations and implementing proper access controls to limit who can perform network filtering modifications. This vulnerability demonstrates the importance of proper memory management practices in kernel code and highlights the need for thorough code review processes to identify similar issues in other kernel subsystems.