CVE-2006-5751 in Linux
Summary
by MITRE
Integer overflow in the get_fdb_entries function in net/bridge/br_ioctl.c in the Linux kernel before 2.6.18.4 allows local users to execute arbitrary code via a large maxnum value in an ioctl request.
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Analysis
by VulDB Data Team • 07/13/2019
The vulnerability identified as CVE-2006-5751 represents a critical integer overflow flaw within the Linux kernel's bridge networking subsystem. This issue specifically affects the get_fdb_entries function located in net/bridge/br_ioctl.c, which handles ioctl requests for bridge forwarding database operations. The vulnerability arises from insufficient input validation when processing the maxnum parameter in ioctl commands, creating a condition where an attacker can manipulate this value to trigger integer overflow behavior. The affected kernel versions prior to 2.6.18.4 demonstrate a fundamental flaw in memory management and input sanitization that directly enables privilege escalation and arbitrary code execution capabilities. This vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited by local users with minimal privileges to gain elevated system access.
The technical implementation of this vulnerability stems from the improper handling of integer arithmetic within the bridge ioctl interface. When a local user submits an ioctl request with an excessively large maxnum value, the kernel's get_fdb_entries function fails to properly validate or clamp this input parameter. The integer overflow occurs during the calculation or allocation process where the large value causes the integer to wrap around to a much smaller number, potentially leading to buffer overflows or memory corruption. This flaw falls under CWE-190, which specifically addresses integer overflow conditions, and more broadly under CWE-122, which covers buffer overflow vulnerabilities. The attack vector is classified as local privilege escalation since the vulnerability requires local system access but does not need network connectivity or specific network conditions to be exploited. The underlying mechanism aligns with ATT&CK technique T1068, which describes the exploitation of legitimate system privileges to gain elevated access.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential system compromise and data integrity threats. Successful exploitation allows attackers to execute arbitrary code with kernel-level privileges, potentially enabling complete system takeover, persistent backdoor installation, or data exfiltration. The vulnerability affects systems running Linux kernel versions below 2.6.18.4, which were widely deployed in enterprise and server environments during that timeframe. Network administrators and system operators face significant risk when deploying systems with vulnerable kernel versions, as the attack surface remains exposed even when other security measures are properly implemented. The implications include potential denial of service conditions, unauthorized access to network resources, and complete compromise of bridged network infrastructure. Organizations utilizing Linux-based networking equipment, virtualization platforms, or bridge-based network configurations are particularly at risk, as these systems rely heavily on the affected kernel functionality. The vulnerability also impacts automated security monitoring systems that depend on predictable kernel behavior, as the overflow can cause unexpected system states that may interfere with security operations.
Mitigation strategies for CVE-2006-5751 focus primarily on kernel version updates and input validation measures. The most effective solution involves upgrading to Linux kernel version 2.6.18.4 or later, where the integer overflow has been patched through proper input validation and boundary checking. System administrators should implement comprehensive patch management procedures to ensure all affected systems receive timely updates. Additionally, organizations can deploy runtime protections such as stack canaries, address space layout randomization, and kernel hardening measures to reduce exploitability. Input validation should be implemented at multiple levels, including application-level checks and kernel-level parameter validation. Network segmentation and privilege separation can help limit the potential impact of successful exploitation, while comprehensive monitoring and logging should be enabled to detect anomalous ioctl activity. Security audits should verify that all bridge-related network functionality properly validates input parameters and implements appropriate bounds checking. The vulnerability serves as a reminder of the critical importance of proper integer handling in kernel code and demonstrates how seemingly minor input validation gaps can result in severe security consequences affecting entire network infrastructures.