# CVE-2026-46242: eventpoll: fix ep_remove struct eventpoll / struct file UAF

> A use-after-free in the Linux kernel's eventpoll subsystem allows attackers to execute arbitrary code or escalate privileges via race conditions.

- **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:** 30 May 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-89159, BELL-CVE-2026-46242, DEBIAN-CVE-2026-46242, GHSA-h4r8-4j67-99mx, ROOT-OS-DEBIAN-12-CVE-2026-46242, ROOT-OS-DEBIAN-13-CVE-2026-46242, ROOT-OS-UBUNTU-2404-CVE-2026-46242, UBUNTU-CVE-2026-46242

## What is CVE-2026-46242?

CVE-2026-46242 is a high-severity use after free vulnerability in Linux kernel, published on 30 May 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:

eventpoll: fix ep_remove struct eventpoll / struct file UAF

ep_remove() (via ep_remove_file()) cleared file->f_ep under
file->f_lock but then kept using @file inside the critical section
(is_file_epoll(), hlist_del_rcu() through the head, spin_unlock).
A concurrent __fput() taking the eventpoll_release() fastpath in
that window observed the transient NULL, skipped
eventpoll_release_file() and ran to f_op->release / file_free().

For the epoll-watches-epoll case, f_op->release is
ep_eventpoll_release() -> ep_clear_and_put() -> ep_free(), which
kfree()s the watched struct eventpoll. Its embedded ->refs
hlist_head is exactly where epi->fllink.pprev points, so the
subsequent hlist_del_rcu()'s "*pprev = next" scribbles into freed
kmalloc-192 memory.

In addition, struct file is SLAB_TYPESAFE_BY_RCU, so the slot
backing @file could be recycled by alloc_empty_file() --
reinitializing f_lock and f_ep -- while ep_remove() is still
nominally inside that lock. The upshot is an attacker-controllable
kmem_cache_free() against the wrong slab cache.

Pin @file via epi_fget() at the top of ep_remove() and gate the
critical section on the pin succeeding. With the pin held @file
cannot reach refcount zero, which holds __fput() off and
transitively keeps the watched struct eventpoll alive across the
hlist_del_rcu() and the f_lock use, closing both UAFs.

If the pin fails @file has already reached refcount zero and its
__fput() is in flight. Because we bailed before clearing f_ep,
that path takes the eventpoll_release() slow path into
eventpoll_release_file() and blocks on ep->mtx until the waiter
side's ep_clear_and_put() drops it. The bailed epi's share of
ep->refcount stays intact, so the trailing ep_refcount_dec_and_test()
in ep_clear_and_put() cannot free the eventpoll out from under
eventpoll_release_file(); the orphaned epi is then cleaned up
there.

A successful pin also proves we are not racing
eventpoll_release_file() on this epi, so drop the now-redundant
re-check of epi->dying under f_lock. The cheap lockless
READ_ONCE(epi->dying) fast-path bailout stays.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-46242?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-46242?

Apply the vendor's patch.

## Is CVE-2026-46242 being exploited?

There is no known exploitation of CVE-2026-46242 in the wild and no public exploit code.

Public exploit code:

- CVE-2026-46242 (github_poc): https://github.com/0xredash/CVE-2026-46242
- CVE-2026-46242 (github_poc): https://github.com/Baba01hacker666/CVE-2026-46242
- Verificador de Vulnerabilidad: Bad Epoll (CVE-2026-46242) (github_poc): https://github.com/SaithFranklinB/ScannerBadEpoll
- https://github.com/villager1314/CVE-2026-46242-Analysis (github_poc): https://github.com/villager1314/CVE-2026-46242-Analysis
- aarch64 race condition checker (github_poc): https://github.com/BinaryMasc/CVE-2026-46242

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-46242 and fix it if it is affected.

What it is: CVE-2026-46242 is a high-severity use after free vulnerability in Linux kernel, published on 30 May 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-2026-46242 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-46242/ (Markdown: https://insights.sbomify.com/CVE-2026-46242/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-46242
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-46242
- OSV: https://osv.dev/vulnerability/CVE-2026-46242

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-46242/
Summaries are generated and may contain mistakes; the official description above is the record.