# CVE-2026-64108: cifs: Fix busy dentry used after unmounting

> A race condition in the Linux kernel CIFS module allows a use-after-free of a dentry during unmount, potentially causing a kernel warning or 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:** 19 Jul 2026
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2026-64108, DEBIAN-CVE-2026-64108, GHSA-3mrw-xf65-fqjh, UBUNTU-CVE-2026-64108

## What is CVE-2026-64108?

CVE-2026-64108 is a high-severity use after free vulnerability in Linux kernel, published on 19 Jul 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: Fix busy dentry used after unmounting

Since commit 340cea84f691c ("cifs: open files should not hold ref on
superblock"), cifs file only holds the dentry ref_cnt, the cifs file
close work(cfile->deferred) could be executed after unmounting, which
will trigger a warning in generic_shutdown_super:
 BUG: Dentry 00000000a14a6845{i=c,n=file}  still in use (1) [unmount of
 cifs cifs]

The detailed processs is:
   process A           process B           kworker
 fd = open(PATH)
  vfs_open
   file->__f_path = *path // dentry->d_lockref.count = 1
   cifs_open
    cifs_new_fileinfo
     cfile->dentry = dget(dentry) // dentry->d_lockref.count = 2
 close(fd)
  __fput
  cifs_close
   queue_delayed_work(deferredclose_wq, cfile->deferred)
  dput(dentry) // dentry->d_lockref.count = 1
			                 smb2_deferred_work_close
					  _cifsFileInfo_put
					   list_del(&cifs_file->flist)
                    umount
		     cleanup_mnt
		      deactivate_super
		       cifs_kill_sb
		        cifs_close_all_deferred_files_sb
			 cifs_close_all_deferred_files
			  // cannot find cfile, skip _cifsFileInfo_put
			kill_anon_super
			 generic_shutdown_super
			  shrink_dcache_for_umount
			   umount_check
			    WARN ! // dentry->d_lockref.count = 1
					   cifsFileInfo_put_final
					    dput(cifs_file->dentry)
		                            // dentry->d_lockref.count = 0

Fix it by flushing 'deferredclose_wq' before calling kill_anon_super.

Fetch a reproducer in https://bugzilla.kernel.org/show_bug.cgi?id=221548.

## Which versions are affected by CVE-2026-64108?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64108?

Apply the vendor's patch.

## Is CVE-2026-64108 being exploited?

There is no known exploitation of CVE-2026-64108 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-2026-64108 and fix it if it is affected.

What it is: CVE-2026-64108 is a high-severity use after free vulnerability in Linux kernel, published on 19 Jul 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-2026-64108 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-2026-64108/ (Markdown: https://insights.sbomify.com/CVE-2026-64108/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64108
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64108
- OSV: https://osv.dev/vulnerability/CVE-2026-64108

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64108/
Summaries are generated and may contain mistakes; the official description above is the record.