CVE-2018-17157 in FreeBSD
Summary
by MITRE
In FreeBSD before 11.2-STABLE(r340854) and 11.2-RELEASE-p5, an integer overflow error when handling opcodes can cause memory corruption by sending a specially crafted NFSv4 request. Unprivileged remote users with access to the NFS server may be able to execute arbitrary code.
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Analysis
by VulDB Data Team • 06/12/2023
The vulnerability identified as CVE-2018-17157 represents a critical integer overflow flaw within the FreeBSD operating system's Network File System version 4 implementation. This security issue affects FreeBSD versions prior to 11.2-STABLE(r340854) and 11.2-RELEASE-p5, where the kernel's handling of specific NFSv4 opcodes contains a mathematical overflow condition that can lead to memory corruption. The flaw exists in the kernel-level NFS server implementation that processes incoming requests from remote clients, making it particularly dangerous as it can be exploited by unauthenticated remote attackers who have network access to the affected system.
The technical implementation of this vulnerability stems from improper bounds checking within the NFSv4 server code when processing certain opcode parameters. Specifically, when the NFS server receives a crafted request containing maliciously formatted opcode data, the integer overflow occurs during arithmetic operations that calculate buffer sizes or array indices. This overflow corrupts adjacent memory locations, potentially allowing an attacker to overwrite critical kernel data structures or function pointers. The vulnerability is classified under CWE-190 as an integer overflow or wraparound, which is a well-documented class of flaws that can lead to arbitrary code execution when memory corruption occurs. The attack vector requires only network access to the NFS server, making it particularly concerning as it can be exploited remotely without authentication.
The operational impact of this vulnerability extends beyond simple privilege escalation as it enables unprivileged remote code execution on systems running affected FreeBSD versions. Attackers can leverage this flaw to gain complete control over the affected NFS server, potentially using it as a foothold for further attacks within the network infrastructure. The memory corruption resulting from the integer overflow can lead to system crashes or more insidiously, allow attackers to inject and execute malicious code with kernel privileges. This vulnerability directly maps to ATT&CK technique T1059.007 for command and script injection, as successful exploitation would enable attackers to execute arbitrary commands on the compromised system. The implications are severe for organizations relying on FreeBSD-based NFS servers, as these systems often serve as critical file sharing infrastructure within enterprise environments.
Mitigation strategies for CVE-2018-17157 primarily involve upgrading to FreeBSD versions 11.2-STABLE(r340854) or 11.2-RELEASE-p5 and later, which contain the necessary patches to prevent the integer overflow condition. System administrators should also implement network segmentation to limit access to NFS servers and disable NFSv4 if not strictly required. Additional defensive measures include monitoring network traffic for suspicious NFSv4 requests and implementing intrusion detection systems that can identify malformed opcode sequences. Organizations should also consider disabling unnecessary NFS features and ensuring that only trusted networks can access NFS services. The vulnerability demonstrates the critical importance of proper input validation and bounds checking in kernel code, particularly when handling network requests that may contain maliciously crafted data. Regular security updates and vulnerability assessments remain essential for maintaining system integrity against similar integer overflow vulnerabilities that could potentially exist in other kernel subsystems.