# CVE-2026-98844: netfs: clear post-EOF pagecache when extending a file via write

> A local attacker can read stale data from the page cache when extending a file via write, 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:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-98844, DEBIAN-CVE-2026-98844, GHSA-vjf5-4hx8-9557, UBUNTU-CVE-2026-98844

## What is CVE-2026-98844?

CVE-2026-98844 is a vulnerability in Linux, published on 18 Oct 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:

netfs: clear post-EOF pagecache when extending a file via write

Fix netfs to erase the contents of a hole created after the EOF by an
ordinary write if dirty data has been previously left there by writes
through an mmapped region.  Neither the buffered nor the unbuffered/DIO
write path clears that stale pagecache.

Zero the tail of the folio straddling the EOF before an extending
write.  That is the only folio that can hold data written past the EOF
through an mmap, as pages wholly beyond the EOF can't be faulted in.
The folio is zeroed rather than dropped so a concurrent extending write
can't lose data.

Both write paths downgrade the i_rwsem to shared, so extending writes
can run concurrently and the i_size read by the caller may be stale by
the time the folio is locked.  Re-read i_size under the folio lock and
clamp the zeroed range up to it, so a racing write that already put
data into the folio isn't clobbered.

Wait for any writeback on the folio to finish before zeroing it so that
the pagecache isn't modified while it may still be read by the transport
during transmission.  Honour IOCB_NOWAIT by returning -EAGAIN rather
than blocking on the folio lock, on writeback, or in folio_mkclean()'s
rmap walk when the folio is mapped.

truncate_pagecache() can't be used here: it must be called with the
i_rwsem held exclusively, but these write paths only hold it shared,
and it would block unconditionally, breaking IOCB_NOWAIT.

Callers that hold i_rwsem exclusively for the whole resize (truncate,
setattr, fallocate, clone) exclude any genuine concurrent buffered
writer, so staleness can instead be decided from the folio's dirty
state, as pagecache_isize_extended() already does for filesystems that
serialise writes against truncate/setattr via a single i_rwsem.
Export netfs_clear_stale_post_isize() helper to handle such case.

The helper is required by the CIFS client to fix generic/363.

## Which versions are affected by CVE-2026-98844?


## How do I fix CVE-2026-98844?

Apply the vendor's patch.

## Is CVE-2026-98844 being exploited?

There is no known exploitation of CVE-2026-98844 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98844 and fix it if it is affected.

What it is: CVE-2026-98844 is a vulnerability in Linux, published on 18 Oct 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-2026-98844 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-2026-98844/ (Markdown: https://insights.sbomify.com/CVE-2026-98844/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98844
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98844
- OSV: https://osv.dev/vulnerability/CVE-2026-98844

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98844/
Summaries are generated and may contain mistakes; the official description above is the record.