CVE-2019-5608 in FreeBSD
Summary
by MITRE
In FreeBSD 12.0-STABLE before r350648, 12.0-RELEASE before 12.0-RELEASE-p9, 11.3-STABLE before r350650, 11.3-RELEASE before 11.3-RELEASE-p2, and 11.2-RELEASE before 11.2-RELEASE-p13, the ICMPv6 input path incorrectly handles cases where an MLDv2 listener query packet is internally fragmented across multiple mbufs. A remote attacker may be able to cause an out-of-bounds read or write that may cause the kernel to attempt to access an unmapped page and subsequently panic.
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Analysis
by VulDB Data Team • 08/10/2020
This vulnerability exists in FreeBSD operating systems across multiple versions including 12.0-STABLE before r350648, 12.0-RELEASE before 12.0-RELEASE-p9, 11.3-STABLE before r350650, 11.3-RELEASE before 11.3-RELEASE-p2, and 11.2-RELEASE before 11.2-RELEASE-p13. The flaw resides in the ICMPv6 input processing pathway specifically when handling MLDv2 listener query packets that are fragmented across multiple mbufs. This represents a critical kernel vulnerability that can lead to system instability and potential exploitation. The issue stems from improper handling of packet fragmentation within the multicast listener discovery version 2 protocol implementation, which is essential for ipv6 multicast communication. When an attacker sends specially crafted fragmented MLDv2 packets, the kernel's packet processing logic fails to correctly manage the boundaries between mbuf segments, creating opportunities for memory access violations.
The technical implementation of this vulnerability involves the kernel's handling of mbuf chains during ICMPv6 packet processing. Mbufs are the fundamental data structures used in FreeBSD for network packet handling, and when packets are fragmented, they are stored across multiple mbufs in a chain. The flaw occurs in the code path that processes MLDv2 listener queries, where the kernel attempts to parse the packet contents without properly accounting for fragmentation boundaries. This mismanagement leads to out-of-bounds memory reads or writes as the kernel traverses the mbuf chain and attempts to access memory locations that are either unmapped or outside the intended data structures. The vulnerability is classified as a buffer over-read or over-write condition that can be triggered by remote attackers without authentication, making it particularly dangerous in networked environments.
The operational impact of this vulnerability is severe as it can cause complete system panics and crashes, effectively leading to denial of service conditions. When the kernel encounters the malformed fragmented packet, it attempts to access unmapped memory pages, which triggers a kernel oops or panic condition. This means that any system running affected FreeBSD versions could be remotely crashed by an attacker sending malicious ICMPv6 packets, potentially affecting network infrastructure, servers, or any device that processes multicast traffic. The vulnerability is particularly concerning because it requires no authentication to exploit and can be triggered from remote locations, making it suitable for widespread denial of service attacks against FreeBSD-based systems.
The root cause of this issue aligns with CWE-129, which addresses improper validation of length of input buffers, and CWE-787, which covers out-of-bounds write operations. From an attack perspective, this vulnerability maps to multiple MITRE ATT&CK techniques including T1499.004 for network denial of service and T1059.001 for command and control through network protocols. The vulnerability represents a classic example of memory safety issues in kernel code where buffer management fails to account for fragmented packet structures, creating opportunities for attackers to manipulate kernel memory. The lack of proper bounds checking when traversing mbuf chains during ICMPv6 processing allows attackers to control memory access patterns and potentially execute arbitrary code if they can control the data being read or written. Organizations should immediately apply the relevant security patches from FreeBSD releases p9, p2, and p13 respectively for the affected versions to remediate this vulnerability.