CVE-2017-7645 in Linux
Summary
by MITRE • 01/25/2023
The NFSv2/NFSv3 server in the nfsd subsystem in the Linux kernel through 4.10.11 allows remote attackers to cause a denial of service (system crash) via a long RPC reply, related to net/sunrpc/svc.c, 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-2017-7645 represents a critical denial of service flaw within the Linux kernel's Network File System version 2 and 3 implementations. This weakness exists in the nfsd subsystem where the kernel fails to properly handle excessively long RPC replies, creating a condition that can be exploited by remote attackers to crash the entire system. The vulnerability specifically affects Linux kernel versions through 4.10.11, making it a widespread concern across numerous production environments that rely on NFS services for file sharing and network storage operations.
The technical root cause of this vulnerability lies in the insufficient input validation mechanisms within the RPC processing code paths. When the nfsd subsystem receives an RPC request that triggers a response exceeding predetermined buffer limits, the kernel's handling routines fail to properly manage the oversized reply. This occurs in the net/sunrpc/svc.c component which manages the service side of RPC communications, along with the fs/nfsd/nfs3xdr.c and fs/nfsd/nfsxdr.c files responsible for encoding and decoding NFS version 3 and generic NFS data transfer operations. The flaw manifests as a buffer overflow condition or memory corruption that ultimately leads to kernel panic and system crash.
The operational impact of CVE-2017-7645 extends beyond simple service disruption to potentially compromising entire network infrastructures that depend on NFS services. Attackers can exploit this vulnerability by crafting malicious RPC requests that generate oversized replies, causing the target system to become unresponsive and requiring manual intervention for recovery. This vulnerability directly maps to CWE-121, which describes heap-based buffer overflow conditions, and aligns with ATT&CK technique T1499.004 for network denial of service attacks. Organizations running NFS servers, particularly those in enterprise environments where file sharing is critical, face significant risk of operational downtime and potential data loss when this vulnerability remains unpatched.
Mitigation strategies for CVE-2017-7645 primarily focus on applying the appropriate kernel security patches released by the Linux kernel development team. System administrators should immediately update their kernels to versions 4.10.12 or later where this vulnerability has been addressed through improved buffer management and input validation routines. Network segmentation and firewall rules can provide temporary protection by limiting access to NFS services, though this approach does not eliminate the underlying vulnerability. Monitoring systems should be configured to detect unusual RPC traffic patterns that might indicate exploitation attempts, and regular vulnerability scanning should be implemented to identify systems running vulnerable kernel versions. The fix implemented in the patched kernels includes enhanced bounds checking in the RPC reply generation process and improved memory management to prevent the conditions that led to system crashes.