# CVE-2026-89600: fanotify: fix use-after-free of file range info

> A use-after-free in the Linux kernel fanotify subsystem allows attackers to read stale stack data or cause a system crash.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-89600, DEBIAN-CVE-2026-89600, GHSA-hfc9-63gq-6mcj, UBUNTU-CVE-2026-89600

## What is CVE-2026-89600?

CVE-2026-89600 is a high-severity use after free 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:

fanotify: fix use-after-free of file range info

fsnotify_pre_content() builds its file_range on the triggering task's
stack. fanotify_alloc_perm_event() saves a pointer to range.pos in the
heap-allocated permission event so copy_range_info_to_user() can report
the offset later.

The event reader can set the event state to FAN_EVENT_REPORTED and then
sleep while preparing the file descriptor. If a signal interrupts the
triggering task at that point, fanotify_get_response() changes the state
to FAN_EVENT_CANCELED and returns. This unwinds the file_range stack
frame while the reader still owns the event. The reader then dereferences
pevent->ppos and copies the stale stack value to userspace.

KASAN reported:

  BUG: KASAN: use-after-free in fanotify_read+0x293e/0x2970
  Read of size 8 at addr ffff88811434fc50 by task fanotify_inotif/95
  Call Trace:
   fanotify_read+0x293e/0x2970
   vfs_read+0x177/0xa20
   ksys_read+0xf7/0x1c0
   do_syscall_64+0xf9/0x540
   entry_SYSCALL_64_after_hwframe+0x77/0x7f

Store the range position directly in the permission event and use
FANOTIFY_NO_RANGE when range information is unavailable. The event remains
alive until the reader finishes, so the reported offset no longer depends
on the triggering task's stack.

## Which versions are affected by CVE-2026-89600?


## How do I fix CVE-2026-89600?

Apply the vendor's patch.

## Is CVE-2026-89600 being exploited?

There is no known exploitation of CVE-2026-89600 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89600 and fix it if it is affected.

What it is: CVE-2026-89600 is a high-severity use after free 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-2026-89600 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-2026-89600/ (Markdown: https://insights.sbomify.com/CVE-2026-89600/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89600
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89600
- OSV: https://osv.dev/vulnerability/CVE-2026-89600

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89600/
Summaries are generated and may contain mistakes; the official description above is the record.