CVE-2009-1897 in Linux
Summary
by MITRE
The tun_chr_poll function in drivers/net/tun.c in the tun subsystem in the Linux kernel 2.6.30 and 2.6.30.1, when the -fno-delete-null-pointer-checks gcc option is omitted, allows local users to gain privileges via vectors involving a NULL pointer dereference and an mmap of /dev/net/tun, a different vulnerability than CVE-2009-1894.
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Analysis
by VulDB Data Team • 12/06/2024
The vulnerability described in CVE-2009-1897 represents a critical privilege escalation flaw within the Linux kernel's tun network subsystem. This issue specifically affects kernel versions 2.6.30 and 2.6.30.1 where the tun_chr_poll function contains a NULL pointer dereference condition that can be exploited by local attackers. The vulnerability arises from the interaction between compiler optimization settings and the kernel's handling of network tunnel devices, creating a path for privilege escalation that leverages the mmap operation on /dev/net/tun. The flaw is distinct from CVE-2009-1894 but shares similar exploitation vectors within the same kernel subsystem, highlighting the complexity of network device driver security in kernel space.
The technical implementation of this vulnerability involves the tun subsystem's character device handling where the tun_chr_poll function fails to properly validate pointer references during certain operations. When the -fno-delete-null-pointer-checks gcc compilation flag is not used, the compiler may optimize away null pointer checks that would normally prevent the dereference. This optimization creates a scenario where a malicious user can manipulate the mmap operation on /dev/net/tun to trigger a NULL pointer dereference within the tun_chr_poll function. The exploitation requires local access to the system since the vulnerability involves kernel memory manipulation and privilege escalation techniques that cannot be performed remotely. The vulnerability operates under CWE-476 which specifically addresses NULL pointer dereference conditions in software systems, making it particularly dangerous in kernel contexts where such dereferences can lead to privilege escalation.
Operationally, this vulnerability presents a significant risk to systems running affected kernel versions as local users can potentially elevate their privileges to root level access. The attack vector requires the attacker to have access to the system and the ability to perform mmap operations on the /dev/net/tun device, which is typically accessible to users with basic system privileges. The exploitation process involves carefully crafted input that causes the kernel to enter a state where it attempts to dereference a NULL pointer, leading to privilege escalation. This vulnerability impacts systems where the tun network subsystem is utilized, particularly those running virtualization environments or systems that rely on network tunneling for various operations. The vulnerability's presence in multiple kernel versions demonstrates how such flaws can persist across releases and require careful patch management to mitigate.
The recommended mitigations for CVE-2009-1897 include applying the appropriate kernel security patches that address the NULL pointer dereference in the tun subsystem. System administrators should ensure that all affected systems are updated to kernel versions that contain the fix for this vulnerability, typically kernel versions 2.6.30.2 and later. Additionally, disabling unnecessary network tunneling capabilities or restricting access to /dev/net/tun can help reduce the attack surface. The vulnerability also highlights the importance of proper compiler optimization flags during kernel compilation, particularly ensuring that null pointer checks are not optimized away. Organizations should implement monitoring for suspicious mmap operations on network device files and consider implementing kernel hardening techniques such as stack canaries and address space layout randomization. This vulnerability serves as a reminder of the critical importance of kernel security and the need for comprehensive testing of kernel code paths, particularly in subsystems that handle user-space interactions and memory management operations. The ATT&CK framework categorizes this as a privilege escalation technique through kernel vulnerabilities, specifically targeting the kernel's memory management subsystem and device driver interfaces.