CVE-2026-89702
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
A vulnerability was fixed in the Linux kernel's nfsd subsystem affecting the nfsd_fh_verify and nfsd_fh_verify_err tracepoints. The server sockaddr slot in the trace buffer was sized by xpt_remotelen but filled with data of length xpt_locallen, so when xpt_locallen exceeded xpt_remotelen, the memcpy wrote past the reserved ring-buffer slot. The issue is reachable for NFSv2/v3 requests over UDP, where xpt_remotelen remains 0 for the transport's lifetime.
Risk Assessment
Writing past the end of the buffer can corrupt kernel memory and potentially lead to a crash or system compromise. In the reverse case (xpt_locallen smaller than xpt_remotelen), the unwritten tail of the slot leaks prior ring-buffer contents to trace consumers, constituting an information disclosure.
Recommendation
Update the Linux kernel to a version containing the fix that sizes the server slot by xpt_locallen. Until the update is applied, consider restricting access to trace interfaces or disabling the nfsd_fh_verify and nfsd_fh_verify_err tracepoints on systems serving NFS over UDP.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: nfsd: size fh_verify server sockaddr slot by xpt_locallen The nfsd_fh_verify and nfsd_fh_verify_err tracepoints declare the server sockaddr slot sized by xpt_remotelen but fill it from xpt_local using xpt_locallen: TP_STRUCT__entry( ... __sockaddr(server, rqstp->rq_xprt->xpt_remotelen) ... ) TP_fast_assign( ... __assign_sockaddr(server, &rqstp->rq_xprt->xpt_local, rqstp->rq_xprt->xpt_locallen); ... ) When xpt_locallen exceeds xpt_remotelen, __assign_sockaddr's memcpy writes past the reserved ring-buffer slot. In the reverse direction (xpt_locallen < xpt_remotelen) the slot is oversized and the unwritten tail leaks prior ring-buffer contents to trace consumers. The write-past-end case is reachable on NFS/UDP. svc_xprt_set_remote() is only called from svc_tcp_accept() (net/sunrpc/svcsock.c) and from the RDMA connect path; svc_create_socket() for UDP calls only svc_xprt_set_local(), so xpt_remotelen stays 0 for the xprt's lifetime. Every fh_verify trace for an NFSv2/v3-over-UDP request then copies 16 or 28 bytes from xpt_local into a zero-byte slot. The other NFSD tracepoints that record the server address (NFSD_TRACE_PROC_CALL_FIELDS, NFSD_TRACE_PROC_RES_FIELDS, SVC_RQST_ENDPOINT_FIELDS) already size the server slot by xpt_locallen; nfsd_fh_verify and nfsd_fh_verify_err were the only exceptions. Fix by sizing the server slot with xpt_locallen so the declared slot matches the copy length. The client slot and its assignment already agree on xpt_remotelen and are left untouched.