CVE-2017-7542 in Linux
Summary
by MITRE
The ip6_find_1stfragopt function in net/ipv6/output_core.c in the Linux kernel through 4.12.3 allows local users to cause a denial of service (integer overflow and infinite loop) by leveraging the ability to open a raw socket.
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Analysis
by VulDB Data Team • 12/13/2022
The vulnerability identified as CVE-2017-7542 represents a critical flaw in the Linux kernel's IPv6 implementation that can be exploited to cause a denial of service condition. This vulnerability resides within the ip6_find_1stfragopt function located in the net/ipv6/output_core.c file, affecting Linux kernel versions through 4.12.3. The flaw manifests when a local attacker with the ability to open a raw socket can manipulate IPv6 packet processing in a manner that triggers both integer overflow conditions and infinite loop scenarios. The vulnerability stems from insufficient input validation and boundary checking during the processing of IPv6 fragments, specifically when handling the first fragment option within IPv6 packets.
The technical exploitation of this vulnerability occurs through the manipulation of raw socket operations that allow users to craft and transmit custom IPv6 packets. When an attacker opens a raw socket and constructs malicious IPv6 packets with specific fragment options, the kernel's ip6_find_1stfragopt function fails to properly validate the fragment header parameters. This validation failure leads to an integer overflow condition where the fragment offset calculations exceed the maximum representable value for the data type being used. The overflow condition then propagates into an infinite loop within the packet processing routine, as the kernel enters a state where it continuously processes the malformed packet without proper termination conditions. This behavior directly violates the principle of bounded execution and can cause the kernel to become unresponsive, effectively rendering the system unavailable to legitimate network traffic.
The operational impact of CVE-2017-7542 extends beyond simple denial of service to potentially compromise system availability and stability. Local users who can open raw sockets, which is typically possible on most Linux systems without special privileges, can exploit this vulnerability to exhaust system resources through the infinite loop mechanism. The integer overflow condition can also potentially lead to memory corruption issues that might be exploitable for privilege escalation under certain circumstances, though the primary impact remains as a denial of service vector. This vulnerability affects systems running Linux kernel versions up to 4.12.3 and represents a fundamental flaw in the kernel's network stack validation logic, particularly for IPv6 packet processing. The issue demonstrates a failure in the kernel's defensive programming practices and highlights the importance of proper input validation in kernel space code.
The vulnerability maps to CWE-191, which describes integer underflow (wrap or wraparound) and CWE-835, which addresses infinite loops. From an ATT&CK perspective, this vulnerability aligns with T1499.004, which covers network denial of service attacks, and T1068, which involves exploiting vulnerabilities in operating systems. The attack vector requires local access and the ability to open raw sockets, making it accessible to any user account on the system. Mitigation strategies include upgrading to Linux kernel version 4.12.4 or later, where the vulnerability has been patched through improved input validation and boundary checking in the ip6_find_1stfragopt function. System administrators should also consider implementing network segmentation and access controls to limit the potential impact of local privilege escalation. Additionally, monitoring for unusual network activity patterns and kernel-level resource consumption can help detect exploitation attempts. The patch addresses the root cause by implementing proper bounds checking on fragment offset calculations and ensuring that the fragment processing loop terminates correctly even when encountering malformed input.