---
id: "CVE-2026-98686"
kind: "vulnerability"
aliases: ["CVE-2026-98686"]
title: "Linux kernel SMB client: stale pagecache data exposed after file extension"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["cifs", "kernel", "linux", "runtime", "self-hosted", "smb"]
not_affected_if: ["cifs-module-not-loaded", "no-smb-mounts"]
published_at: "2026-10-18T16:17:21+00:00"
first_seen_at: "2026-10-23T21:57:16+00:00"
updated_at: "2026-10-25T05:19:09+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98686", "first_seen_at": "2026-10-23T21:57:16+00:00"}]
---

# Linux kernel SMB client: stale pagecache data exposed after file extension

When the Linux kernel's SMB client extends a file using zero-range, it leaves pagecache data dirtied past the old end of file in place, so that data becomes visible as file content. The sources describe a data exposure from stale cached pages and do not state an attacker-controlled trigger.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the running kernel version with `uname -r` and compare it against the fixed kernel release in the NVD entry (unknown in the sources).
- Check whether the SMB client module is loaded with `lsmod | grep cifs`.

## Fix

- Update the Linux kernel to a release that includes the upstream commit for smb: client: discard post-EOF pagecache when extending a file via zero range (version unknown in the sources).

## Timeline

- 2026-10-23T21:57:16+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98686

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

smb: client: discard post-EOF pagecache when extending a file via zero range

smb3_zero_range() removed the pagecache only for the range being zeroed,
so when it extends the file the folio straddling the old EOF - which may
hold data dirtied past EOF through an mmap - was never dropped and became
visible as file content once the file was extended.

Lower the discard boundary to the smaller of the zero-range offset and the
old EOF.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_