CVE-2011-1768 in Linux
Summary
by MITRE
The tunnels implementation in the Linux kernel before 2.6.34, when tunnel functionality is configured as a module, allows remote attackers to cause a denial of service (OOPS) by sending a packet during module loading.
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Analysis
by VulDB Data Team • 12/03/2021
The vulnerability identified as CVE-2011-1768 represents a critical race condition flaw in the Linux kernel's tunnel implementation that affects versions prior to 2.6.34. This issue specifically manifests when tunnel functionality is configured as a loadable kernel module rather than being built into the kernel. The flaw occurs during the dynamic loading process of the tunnel module, creating a window where remote attackers can exploit the timing gap between module initialization and proper state establishment. The vulnerability is classified under CWE-362, which addresses race conditions in kernel space operations, making it particularly dangerous as it can be triggered remotely without requiring local access or authentication. The attack vector leverages packet injection during the module loading phase, where malicious actors can send specially crafted packets that cause the kernel to crash with an OOPS error, effectively leading to a system denial of service condition.
The technical exploitation of this vulnerability exploits fundamental timing issues within kernel module loading mechanisms. When the tunnel module is dynamically loaded, the kernel's module management system creates a temporary state where certain data structures may not be fully initialized or properly protected. Remote attackers can send packets that target these uninitialized or improperly protected kernel memory regions during the loading sequence, causing the kernel to execute invalid memory operations and subsequently crash. This type of vulnerability falls under the ATT&CK technique T1499.004, which covers network denial of service attacks, and specifically represents a kernel-level privilege escalation vector that can be exploited from remote locations. The OOPS condition generated by the exploitation results in immediate system instability, with the kernel's panic handler being invoked and potentially leading to complete system shutdown or reboot.
The operational impact of CVE-2011-1768 extends beyond simple denial of service, as it can be weaponized to disrupt critical infrastructure services that rely on tunneling protocols such as ipip, sit, or other network tunnel implementations. Systems running vulnerable kernel versions may experience unexpected downtime, particularly in environments where tunneling is frequently used for network virtualization, traffic forwarding, or secure communication channels. The vulnerability affects a broad range of network configurations where tunnel modules are dynamically loaded, including enterprise networks, cloud infrastructure, and embedded systems that utilize Linux-based networking stacks. Organizations running affected kernel versions face significant operational risk as this vulnerability can be exploited by automated scanning tools or malicious actors without requiring special privileges or access credentials. The exploitation requires only basic network connectivity to send packets to the target system, making it particularly dangerous for publicly exposed network services that utilize tunneling functionality.
Mitigation strategies for CVE-2011-1768 primarily focus on kernel version upgrades to 2.6.34 or later, which contain patches that address the race condition in module loading. System administrators should prioritize immediate kernel updates across all affected systems, particularly those running tunneling services or network infrastructure components. Alternative mitigations include disabling tunnel modules when not actively needed, implementing strict network access controls to limit exposure to unauthorized packet injection, and monitoring for unusual network traffic patterns that might indicate exploitation attempts. Organizations should also consider implementing intrusion detection systems that can identify potential exploitation attempts targeting kernel-level vulnerabilities. The patch addressing this vulnerability implements proper locking mechanisms and state validation during module loading, preventing the race condition that allowed attackers to trigger the OOPS condition. Security teams should conduct comprehensive vulnerability assessments to identify all systems running vulnerable kernel versions and establish monitoring procedures to detect potential exploitation attempts. This vulnerability highlights the importance of secure coding practices in kernel space and demonstrates how seemingly minor timing issues can result in catastrophic system failures, emphasizing the need for thorough testing of kernel module loading sequences and proper synchronization mechanisms.