# CVE-2026-89642: cifs: call pagecache_isize_extended() in cifs_setsize() when extending

> A local attacker can read stale memory data from the page cache when extending a CIFS file size, potentially exposing sensitive information.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-100884, BELL-CVE-2026-89642, DEBIAN-CVE-2026-89642, GHSA-cjwf-376p-qpm9, UBUNTU-CVE-2026-89642

## What is CVE-2026-89642?

CVE-2026-89642 is a vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

cifs: call pagecache_isize_extended() in cifs_setsize() when extending

cifs_setsize() calls truncate_pagecache() but skips
pagecache_isize_extended() on extension.  truncate_setsize() shows
the correct pattern:

  i_size_write(inode, newsize);
  if (newsize > oldsize)
      pagecache_isize_extended(inode, oldsize, newsize);
  truncate_pagecache(inode, newsize);

pagecache_isize_extended() zeroes the tail of the page straddling old
EOF.  Without it, dirty bytes in that region can be written back to
the server, exposing stale data in the newly extended range.

## Which versions are affected by CVE-2026-89642?


## How do I fix CVE-2026-89642?

Apply the vendor's patch.

## Is CVE-2026-89642 being exploited?

There is no known exploitation of CVE-2026-89642 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89642 and fix it if it is affected.

What it is: CVE-2026-89642 is a vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89642 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-89642/ (Markdown: https://insights.sbomify.com/CVE-2026-89642/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89642
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89642
- OSV: https://osv.dev/vulnerability/CVE-2026-89642

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89642/
Summaries are generated and may contain mistakes; the official description above is the record.