# CVE-2026-31465: writeback: don't block sync for filesystems with no data integrity guarantees

> A flaw in the Linux kernel writeback mechanism causes system hangs during suspend when using filesystems without data integrity guarantees, such as FUSE.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 22 Apr 2026
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2026-31465, DEBIAN-CVE-2026-31465, GHSA-3wmh-pgp5-9q7q, UBUNTU-CVE-2026-31465

## What is CVE-2026-31465?

CVE-2026-31465 is a medium-severity denial of service vulnerability in Linux kernel, published on 22 Apr 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:

writeback: don't block sync for filesystems with no data integrity guarantees

Add a SB_I_NO_DATA_INTEGRITY superblock flag for filesystems that cannot
guarantee data persistence on sync (eg fuse). For superblocks with this
flag set, sync kicks off writeback of dirty inodes but does not wait
for the flusher threads to complete the writeback.

This replaces the per-inode AS_NO_DATA_INTEGRITY mapping flag added in
commit f9a49aa302a0 ("fs/writeback: skip AS_NO_DATA_INTEGRITY mappings
in wait_sb_inodes()"). The flag belongs at the superblock level because
data integrity is a filesystem-wide property, not a per-inode one.
Having this flag at the superblock level also allows us to skip having
to iterate every dirty inode in wait_sb_inodes() only to skip each inode
individually.

Prior to this commit, mappings with no data integrity guarantees skipped
waiting on writeback completion but still waited on the flusher threads
to finish initiating the writeback. Waiting on the flusher threads is
unnecessary. This commit kicks off writeback but does not wait on the
flusher threads. This change properly addresses a recent report [1] for
a suspend-to-RAM hang seen on fuse-overlayfs that was caused by waiting
on the flusher threads to finish:

Workqueue: pm_fs_sync pm_fs_sync_work_fn
Call Trace:
 <TASK>
 __schedule+0x457/0x1720
 schedule+0x27/0xd0
 wb_wait_for_completion+0x97/0xe0
 sync_inodes_sb+0xf8/0x2e0
 __iterate_supers+0xdc/0x160
 ksys_sync+0x43/0xb0
 pm_fs_sync_work_fn+0x17/0xa0
 process_one_work+0x193/0x350
 worker_thread+0x1a1/0x310
 kthread+0xfc/0x240
 ret_from_fork+0x243/0x280
 ret_from_fork_asm+0x1a/0x30
 </TASK>

On fuse this is problematic because there are paths that may cause the
flusher thread to block (eg if systemd freezes the user session cgroups
first, which freezes the fuse daemon, before invoking the kernel
suspend. The kernel suspend triggers ->write_node() which on fuse issues
a synchronous setattr request, which cannot be processed since the
daemon is frozen. Or if the daemon is buggy and cannot properly complete
writeback, initiating writeback on a dirty folio already under writeback
leads to writeback_get_folio() -> folio_prepare_writeback() ->
unconditional wait on writeback to finish, which will cause a hang).
This commit restores fuse to its prior behavior before tmp folios were
removed, where sync was essentially a no-op.

[1] https://lore.kernel.org/linux-fsdevel/CAJnrk1a-asuvfrbKXbEwwDSctvemF+6zfhdnuzO65Pt8HsFSRw@mail.gmail.com/T/#m632c4648e9cafc4239299887109ebd880ac6c5c1

## Which versions are affected by CVE-2026-31465?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31465?

Apply the vendor's patch.

## Is CVE-2026-31465 being exploited?

There is no known exploitation of CVE-2026-31465 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-2026-31465 and fix it if it is affected.

What it is: CVE-2026-31465 is a medium-severity denial of service vulnerability in Linux kernel, published on 22 Apr 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-2026-31465 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-2026-31465/ (Markdown: https://insights.sbomify.com/CVE-2026-31465/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31465
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31465
- OSV: https://osv.dev/vulnerability/CVE-2026-31465

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31465/
Summaries are generated and may contain mistakes; the official description above is the record.