CVE-2026-98250 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
nfsd: fix handling of NFSEXP_PNFS in the netlink codepath
The rework of how block layouts were checked moved the check for NFSEXP_PNFS out of nfsd4_setup_layout_type() and into the callers. That patch didn't account for the new call in nfsd4_setup_layout_type().
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Analysis
by VulDB Data Team • 10/06/2026
This vulnerability involves a regression in the Linux kernel's Network File System daemon, specifically within the netlink codepath responsible for handling NFSv4 layout types. The issue stems from a recent refactoring effort aimed at improving how block layouts are validated during the setup process. Previously, the check for the NFSEXP_PNFS flag was integrated directly into the nfsd4_setup_layout_type function. However, as part of an optimization to move this validation logic closer to its point of use, developers relocated the NFSEXP_PNFS verification from within that specific function to its various callers. This architectural change intended to streamline the code flow and reduce redundancy in layout type initialization routines.
The critical flaw arises because the refactoring did not adequately account for all invocation contexts of nfsd4_setup_layout_type. Specifically, while most call sites were updated to perform the necessary NFSEXP_PNFS checks before invoking the function, at least one path remained unmodified or incorrectly handled this dependency. This oversight means that in certain scenarios involving netlink interactions with the NFS server component, the system may proceed without verifying whether PNFS (Parallel NFS) extensions are properly enabled and configured for the specific export being accessed. The absence of this validation step creates a gap in the security boundary enforcement mechanisms inherent to the kernel's network file serving subsystem.
From an operational perspective, this defect can lead to inconsistent behavior when clients attempt to establish layouts under conditions where PNFS support is either disabled or misconfigured on the server side. Depending on how the underlying code handles the missing flag check, this could result in undefined behavior, potential crashes within the kernel space due to null pointer dereferences or invalid memory accesses, or more subtly, a bypass of intended access controls related to parallel file system operations. Such inconsistencies undermine the reliability and stability of NFS services, particularly in environments relying on high-performance storage architectures that depend heavily on correct PNFS implementation details.
This type of error aligns with CWE-20 Improper Input Validation, as the software fails to properly verify essential configuration flags before proceeding with critical initialization steps. It also relates to CWE-841 Improper Enforcement of Behavioral Workflow, where the sequence of operations required for secure setup is disrupted by incomplete refactoring. In terms of MITRE ATT&CK mapping, this vulnerability could potentially be leveraged in conjunction with other exploits to achieve denial-of-service conditions against NFS infrastructure or, if combined with memory corruption issues elsewhere, might facilitate privilege escalation attacks targeting kernel-level resources.
Mitigation strategies primarily involve applying the upstream Linux kernel patch that resolves this specific oversight by ensuring all call sites of nfsd4_setup_layout_type correctly enforce the NFSEXP_PNFS check regardless of their origin. System administrators should prioritize updating to a patched version of the operating system or kernel package where this logic has been corrected. Until patches are applied, monitoring logs for unusual NFS-related errors or crashes can help detect potential exploitation attempts. Additionally, reviewing network configurations to ensure PNFS is explicitly and correctly enabled only when intended reduces the attack surface associated with misconfigured layout requests.