CVE-2007-5501 in Linux
Summary
by MITRE
The tcp_sacktag_write_queue function in net/ipv4/tcp_input.c in Linux kernel 2.6.21 through 2.6.23.7, and 2.6.24-rc through 2.6.24-rc2, allows remote attackers to cause a denial of service (crash) via crafted ACK responses that trigger a NULL pointer dereference.
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Analysis
by VulDB Data Team • 08/01/2019
The vulnerability identified as CVE-2007-5501 represents a critical denial of service flaw within the Linux kernel's TCP implementation that affects versions from 2.6.21 through 2.6.23.7 and the corresponding 2.6.24-rc releases. This issue resides in the tcp_sacktag_write_queue function located in the net/ipv4/tcp_input.c source file, where a specific condition allows remote attackers to manipulate network traffic in a manner that leads to system instability. The flaw specifically manifests when crafted ACK responses are sent to a target system, triggering an unexpected NULL pointer dereference that ultimately results in kernel crash and system unavailability.
The technical mechanism behind this vulnerability involves the manipulation of TCP Selective Acknowledgment (SACK) functionality during the transmission of network packets. When the kernel processes these specially crafted ACK packets, the tcp_sacktag_write_queue function fails to properly validate certain pointer references, leading to a scenario where a NULL pointer is dereferenced during the packet processing routine. This particular code path within the TCP input handling module does not adequately handle edge cases involving SACK data structures, creating a condition where remote adversaries can force the kernel into an invalid memory access state. The vulnerability is particularly concerning because it can be exploited without requiring authentication or special privileges, making it accessible to any remote attacker who can establish network connectivity to the target system.
The operational impact of CVE-2007-5501 extends beyond simple service disruption to potentially compromising system availability and stability in environments where network connectivity is critical. Systems running affected kernel versions become vulnerable to remote exploitation, allowing attackers to cause immediate system crashes and subsequent denial of service conditions that may require manual intervention to restore normal operations. This vulnerability directly maps to CWE-476 which describes NULL pointer dereference conditions, and it aligns with ATT&CK technique T1499.004 for network denial of service attacks. Organizations running affected systems face significant risk of service interruption, particularly in high-availability environments where such crashes could lead to cascading failures or require extensive downtime for system recovery and patch deployment.
Mitigation strategies for this vulnerability primarily focus on immediate kernel updates and patches that address the NULL pointer dereference issue within the tcp_sacktag_write_queue function. System administrators should prioritize upgrading to kernel versions that have been patched to properly validate pointer references and handle SACK data structures correctly. Additionally, network administrators can implement temporary network-level mitigations such as packet filtering rules that limit the types of TCP ACK packets accepted from untrusted sources, though this approach may impact legitimate network traffic. The vulnerability demonstrates the importance of thorough input validation in kernel space code and highlights the critical need for maintaining up-to-date system software to protect against known exploits. Organizations should also consider implementing intrusion detection systems that can identify suspicious TCP packet patterns associated with this specific vulnerability to provide early warning of potential attacks.