CVE-2026-89674

Received Received - Intake

Buffer Overflow in Linux Kernel NFS Daemon

Publication date: 2026-09-11

Last updated on: 2026-09-14

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix XDR length calculation in nfsd4_ff_encode_layoutget The XDR buffer size calculation in nfsd4_ff_encode_layoutget() has multiple errors that can result in either an out-of-bounds write or leaking uninitialized kernel memory to the client: - fh_len doesn't account for XDR padding on the file handle data - uid and gid lengths use "8 + len" but xdr_encode_opaque() actually writes "4 + xdr_align_size(len)" bytes - ds_len omits the flags and stats_collect_hint fields (8 bytes), while len's header constant overestimates by 8 bytes -- these partially cancel but leave a net mismatch The worst case occurs with short strings (e.g. uid=0, gid=0 with an odd-sized file handle), where the function writes up to 5 bytes past the reserved XDR buffer. Conversely, when string lengths happen to be 4-byte aligned, the reservation is too large and stale buffer content is sent to the client. Fix this by breaking out every encoded field explicitly in the ds_len calculation, using xdr_align_size() for all variable-length opaque fields, and correcting the header constants.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-09-11

Last Modified

2026-09-14

Generated

2026-10-02

AI Q&A

2026-09-12

EPSS Evaluated

2026-10-01

NVD

CVE-2026-89674

EUVD

EUVD-2026-76586

Affected Vendors & Products

Vendor	Product	Version / Range
linux	linux_kernel	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This is a Linux kernel vulnerability in the NFS server (nfsd) where incorrect XDR buffer size calculations in nfsd4_ff_encode_layoutget() can cause memory corruption or data leaks. The function miscalculates lengths for file handles, user IDs, and group IDs, leading to either writing past buffer limits or sending stale memory contents to clients.

Detection Guidance

This vulnerability is specific to the Linux kernel's NFS server implementation and requires kernel-level inspection. Detection involves checking kernel logs for NFS-related errors or monitoring for unusual memory access patterns in NFS operations. Commands like dmesg | grep nfsd or journalctl -k | grep nfsd may show related errors. However, no direct detection commands are provided in the context.

Impact Analysis

An attacker could exploit this to crash the system, corrupt data, or leak sensitive kernel memory to clients. Systems using NFSv4 with file layout operations are most at risk. The impact depends on the specific miscalculation scenario but could include denial of service or information disclosure.

Compliance Impact

This vulnerability could lead to unauthorized data exposure, violating GDPR's data protection principles or HIPAA's confidentiality requirements. If exploited, it may result in data breaches, triggering compliance violations and potential regulatory penalties.

Mitigation Strategies

Apply the kernel patch that fixes the XDR length calculation in nfsd4_ff_encode_layoutget. Update your Linux kernel to a version containing the fix. If immediate patching is not possible, consider disabling NFSv4 features or restricting NFS access until the patch is applied.

Hi! I’m here to help you understand CVE-2026-89674. Ask me anything about the vulnerability, its impact, or mitigation strategies.

0/70