CVE-2011-4112 in Linux
Summary
by MITRE
The net subsystem in the Linux kernel before 3.1 does not properly restrict use of the IFF_TX_SKB_SHARING flag, which allows local users to cause a denial of service (panic) by leveraging the CAP_NET_ADMIN capability to access /proc/net/pktgen/pgctrl, and then using the pktgen package in conjunction with a bridge device for a VLAN interface.
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Analysis
by VulDB Data Team • 12/01/2021
The vulnerability described in CVE-2011-4112 represents a critical flaw in the Linux kernel's networking subsystem that existed prior to version 3.1. This issue specifically targets the net subsystem's handling of network interface flags, particularly the IFF_TX_SKB_SHARING flag which controls how network packets are transmitted through shared kernel data structures. The vulnerability arises from insufficient validation mechanisms that should have prevented unauthorized manipulation of this critical network flag, creating a pathway for malicious local users to exploit the system's networking infrastructure.
The technical exploitation of this vulnerability requires a local attacker to possess the CAP_NET_ADMIN capability, which grants administrative privileges over network operations within the Linux system. Attackers can leverage this capability to access the /proc/net/pktgen/pgctrl interface, which serves as a control mechanism for the packet generator tool. The pktgen package, when combined with bridge device operations on VLAN interfaces, creates a specific scenario where the IFF_TX_SKB_SHARING flag can be improperly manipulated. This manipulation leads to a kernel panic condition where the system becomes unstable and unresponsive, effectively causing a denial of service attack that can bring the entire system to a halt.
The operational impact of this vulnerability extends beyond simple service disruption as it represents a fundamental flaw in kernel memory management and network interface handling. When a kernel panic occurs due to improper flag handling, the system cannot recover gracefully and must be rebooted to restore functionality. This vulnerability is particularly dangerous in production environments where system uptime is critical, as it can be exploited by any local user with network administration privileges to cause significant service interruptions. The vulnerability also demonstrates poor adherence to security principles in kernel design, as it fails to implement proper input validation and privilege checks for critical network operations.
The flaw aligns with CWE-248, which addresses "Uncaught Exception" in software systems, as the kernel fails to properly handle edge cases when processing network interface flags. From an ATT&CK framework perspective, this vulnerability maps to T1068, "Exploitation for Privilege Escalation," and T1499, "Endpoint Denial of Service," as it allows local users to escalate their privileges through network administration capabilities and subsequently cause system-wide denial of service conditions. The vulnerability also relates to T1059, "Command and Scripting Interpreter," as exploitation involves the use of kernel-level tools and interfaces to manipulate system behavior.
Mitigation strategies for CVE-2011-4112 require immediate system updates to kernel versions 3.1 or later where the vulnerability has been patched. Organizations should also implement strict access controls to prevent unauthorized local users from obtaining CAP_NET_ADMIN privileges, particularly in multi-user environments where such capabilities should be restricted to only trusted administrators. Network administrators should monitor for unusual packet generation activities and implement proper logging of network interface changes to detect potential exploitation attempts. Additionally, system hardening practices should include disabling unnecessary network debugging interfaces and restricting access to /proc/net/pktgen/pgctrl through file system permissions. Regular security audits should verify that network administration capabilities are properly restricted and that kernel versions are maintained at supported releases to prevent exploitation of known vulnerabilities.