CVE-2013-3266 in FreeBSD
Summary
by MITRE
The nfsrvd_readdir function in sys/fs/nfsserver/nfs_nfsdport.c in the new NFS server in FreeBSD 8.0 through 9.1-RELEASE-p3 does not verify that a READDIR request is for a directory node, which allows remote attackers to cause a denial of service (memory corruption) or possibly execute arbitrary code by specifying a plain file instead of a directory.
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Analysis
by VulDB Data Team • 05/10/2021
The vulnerability identified as CVE-2013-3266 resides within the FreeBSD operating system's Network File System implementation, specifically affecting versions 8.0 through 9.1-RELEASE-p3. This flaw exists in the nfsrvd_readdir function located in the file sys/fs/nfsserver/nfs_nfsdport.c, which handles the server-side operations for NFS version 2 and 3 protocols. The issue represents a critical security weakness that could potentially allow remote attackers to manipulate the system's memory management and execute arbitrary code, making it particularly dangerous for networked environments where NFS services are actively utilized.
The technical root cause of this vulnerability stems from insufficient input validation within the NFS server implementation. When processing READDIR requests, the nfsrvd_readdir function fails to properly verify whether the requested file handle corresponds to a directory node as expected for directory listing operations. This validation gap allows attackers to submit a READDIR request targeting a regular file instead of a directory, bypassing the normal access control checks that should prevent such operations. The function's lack of proper node type verification creates a condition where the server attempts to process file data as if it were directory entries, leading to memory corruption during the parsing and response generation phases.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it potentially enables remote code execution capabilities. When an attacker successfully exploits this flaw by targeting a regular file with a READDIR request, the server's memory management structures become corrupted through improper pointer dereferencing and buffer manipulation. This memory corruption can manifest in various ways including system crashes, unpredictable behavior, or in more severe cases, allow attackers to inject and execute malicious code within the context of the NFS server process. The vulnerability is particularly concerning because it affects the core NFS server functionality that many systems rely upon for file sharing and network storage operations.
From a cybersecurity perspective, this vulnerability aligns with CWE-125, which describes "Out-of-bounds Read" conditions that can occur when software does not properly validate input data before processing. The flaw also demonstrates characteristics of privilege escalation and memory corruption patterns typically associated with the MITRE ATT&CK framework's technique T1068, which covers "Exploitation for Privilege Escalation." The vulnerability's exploitation requires network access to the affected NFS server and can be automated, making it a significant threat vector for attackers seeking to compromise FreeBSD systems. Organizations should consider implementing network segmentation, disabling unnecessary NFS services, and applying the relevant security patches immediately upon release to mitigate this risk.
The remediation approach for CVE-2013-3266 involves upgrading to FreeBSD versions that contain the patched implementation of the nfsrvd_readdir function, specifically versions beyond 9.1-RELEASE-p3. System administrators should also implement network monitoring to detect anomalous READDIR requests and consider disabling NFSv2 if NFSv3 is sufficient for operational requirements. The patch addresses the core validation issue by ensuring that all READDIR requests are properly verified to target directory nodes before processing, preventing the memory corruption that would otherwise occur during malformed request handling. Security teams should conduct comprehensive vulnerability assessments to identify all systems running affected FreeBSD versions and prioritize remediation efforts based on the criticality of NFS services within their network infrastructure.