CVE-2017-6214 in Linux
Summary
by MITRE
The tcp_splice_read function in net/ipv4/tcp.c in the Linux kernel before 4.9.11 allows remote attackers to cause a denial of service (infinite loop and soft lockup) via vectors involving a TCP packet with the URG flag.
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Analysis
by VulDB Data Team • 12/25/2024
The vulnerability identified as CVE-2017-6214 represents a critical denial of service flaw within the Linux kernel's TCP implementation that affects versions prior to 4.9.11. This issue resides in the tcp_splice_read function located in the net/ipv4/tcp.c file, which handles the reading of TCP data for splice operations. The vulnerability specifically manifests when processing TCP packets that contain the urgent flag set, creating a condition that can lead to system instability and complete service disruption. The flaw demonstrates the dangerous potential of improper input validation within kernel space code, where malicious network traffic can trigger catastrophic system behavior without requiring authentication or elevated privileges.
The technical root cause of this vulnerability stems from a logic error in how the kernel processes TCP packets with the urgent flag during splice operations. When a TCP packet arrives with the URG flag set, the tcp_splice_read function enters an infinite loop condition that prevents proper packet processing and eventually leads to a soft lockup state. This occurs because the function fails to properly handle the interaction between urgent pointer processing and the splice read mechanism, creating a scenario where the kernel thread becomes trapped in a loop that consumes CPU resources indefinitely. The vulnerability operates at the kernel level, making it particularly dangerous as it bypasses normal user-space protections and can affect any system running vulnerable kernel versions regardless of network configuration or firewall settings.
The operational impact of CVE-2017-6214 extends beyond simple service disruption to potentially compromise entire system availability. An attacker can trigger this vulnerability by sending specially crafted TCP packets with the urgent flag set to any reachable system running an affected kernel version. The resulting infinite loop causes the system to become unresponsive, effectively rendering it unusable for legitimate network operations while consuming significant CPU resources. This type of denial of service attack can be particularly devastating in production environments where system uptime is critical, as it can take hours or days to recover from the soft lockup state without manual intervention or system reboot. The vulnerability aligns with CWE-835, which describes the weakness of infinite loops in software systems, and demonstrates how such flaws can be exploited in kernel space to create persistent availability issues.
Mitigation strategies for CVE-2017-6214 focus primarily on kernel version upgrades to 4.9.11 or later, which contain the necessary patches to resolve the infinite loop condition in tcp_splice_read. System administrators should prioritize patching affected systems, particularly those exposed to untrusted network traffic or running critical services. Additional defensive measures include implementing network-level firewalls to filter TCP packets with suspicious urgent flag combinations and monitoring for unusual CPU usage patterns that might indicate exploitation attempts. The vulnerability also highlights the importance of kernel security testing and proper input validation in network stack implementations, as it demonstrates how seemingly minor protocol flag interactions can create major system stability issues. Organizations should maintain updated security patches and conduct regular vulnerability assessments to prevent exploitation of similar kernel-level flaws that could potentially allow privilege escalation or more sophisticated attack vectors. This vulnerability serves as a reminder of the critical importance of kernel security and proper code review processes in preventing remote code execution and denial of service conditions that can affect system availability and integrity.