# CVE-2026-31718: ksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger

> A use-after-free in the Linux kernel ksmbd module allows attackers to execute code or escalate privileges via durable file handle cleanup.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 May 2026
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2026-31718, DEBIAN-CVE-2026-31718, GHSA-24c9-h3qq-j27f, UBUNTU-CVE-2026-31718

## What is CVE-2026-31718?

CVE-2026-31718 is a critical use after free vulnerability in Linux kernel, published on 1 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

ksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger

When a durable file handle survives session disconnect (TCP close without
SMB2_LOGOFF), session_fd_check() sets fp->conn = NULL to preserve the
handle for later reconnection. However, it did not clean up the byte-range
locks on fp->lock_list.

Later, when the durable scavenger thread times out and calls
__ksmbd_close_fd(NULL, fp), the lock cleanup loop did:

    spin_lock(&fp->conn->llist_lock);

This caused a slab use-after-free because fp->conn was NULL and the
original connection object had already been freed by
ksmbd_tcp_disconnect().

The root cause is asymmetric cleanup: lock entries (smb_lock->clist) were
left dangling on the freed conn->lock_list while fp->conn was nulled out.

To fix this issue properly, we need to handle the lifetime of
smb_lock->clist across three paths:
 - Safely skip clist deletion when list is empty and fp->conn is NULL.
 - Remove the lock from the old connection's lock_list in
   session_fd_check()
 - Re-add the lock to the new connection's lock_list in
   ksmbd_reopen_durable_fd().

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-31718?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31718?

Apply the vendor's patch.

## Is CVE-2026-31718 being exploited?

There is no known exploitation of CVE-2026-31718 in the wild and no public exploit code.

## 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-2026-31718 and fix it if it is affected.

What it is: CVE-2026-31718 is a critical use after free vulnerability in Linux kernel, published on 1 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-31718 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-2026-31718/ (Markdown: https://insights.sbomify.com/CVE-2026-31718/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31718
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31718
- OSV: https://osv.dev/vulnerability/CVE-2026-31718

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31718/
Summaries are generated and may contain mistakes; the official description above is the record.