CVE-2017-7895 in Linux
Summary
by MITRE • 01/25/2023
The NFSv2 and NFSv3 server implementations in the Linux kernel through 4.10.13 lack certain checks for the end of a buffer, which allows remote attackers to trigger pointer-arithmetic errors or possibly have unspecified other impact via crafted requests, related to fs/nfsd/nfs3xdr.c and fs/nfsd/nfsxdr.c.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability identified as CVE-2017-7895 represents a critical buffer overflow condition affecting the Network File System implementations in Linux kernel versions through 4.10.13. This flaw exists within the NFSv2 and NFSv3 server components, specifically in the xdr (External Data Representation) processing functions located in fs/nfsd/nfs3xdr.c and fs/nfsd/nfsxdr.c. The root cause stems from insufficient boundary checking during the parsing of network requests, creating opportunities for malicious actors to manipulate buffer pointers through carefully crafted network packets. The vulnerability classifies under CWE-129 as an insufficient bound checking issue, where the system fails to validate input boundaries before processing potentially malicious data.
The technical exploitation of this vulnerability occurs when remote attackers send specially crafted NFS requests that cause the kernel's NFS server implementation to perform invalid pointer arithmetic operations. These malformed requests exploit the absence of proper buffer end checks, allowing attackers to manipulate memory locations beyond the intended buffer boundaries. The impact ranges from triggering kernel crashes and system instability to potentially enabling remote code execution depending on the specific memory corruption patterns. The vulnerability affects the core kernel networking stack and represents a privilege escalation vector since NFS server processes typically run with elevated privileges. This flaw directly aligns with ATT&CK technique T1068 which involves exploiting legitimate credentials and system access for privilege escalation.
The operational impact of CVE-2017-7895 extends beyond simple system crashes, as it can lead to complete system compromise when exploited successfully. Organizations running vulnerable NFS servers face potential data loss, service disruption, and unauthorized access to network resources. The vulnerability affects systems where NFSv2 and NFSv3 protocols are actively used for file sharing, making it particularly dangerous in enterprise environments where file servers and storage systems rely on these protocols. Attackers can leverage this vulnerability to gain persistent access to networked systems, potentially establishing backdoors or escalating privileges to root level access. The lack of proper input validation in the xdr processing functions creates a pathway for attackers to manipulate kernel memory structures and execute arbitrary code with kernel-level privileges.
Mitigation strategies for CVE-2017-7895 require immediate kernel updates to versions 4.10.14 or later, where the buffer boundary checking has been properly implemented. System administrators should disable NFSv2 and NFSv3 protocols if they are not actively required, as NFSv4 provides better security features and is less susceptible to similar vulnerabilities. Network segmentation and firewall rules should be implemented to restrict NFS server access to trusted networks only, reducing the attack surface. Additionally, monitoring for unusual NFS traffic patterns and implementing intrusion detection systems can help identify potential exploitation attempts. Organizations should conduct thorough vulnerability assessments to identify all systems running vulnerable kernel versions and ensure proper patch management procedures are in place to prevent future occurrences of similar buffer overflow vulnerabilities. The fix implemented in the patched kernel versions addresses the specific buffer overflow conditions in the xdr processing code, ensuring proper validation of input data before memory operations are performed.