# CVE-2026-31450: ext4: publish jinode after initialization

> A race condition in the Linux kernel ext4 filesystem allows a local attacker to cause a system crash by triggering a null pointer dereference during fast commit flush.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Apr 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-83375, BELL-CVE-2026-31450, DEBIAN-CVE-2026-31450, GHSA-fr68-gvh3-4qhv, ROOT-OS-DEBIAN-11-CVE-2026-31450, ROOT-OS-DEBIAN-12-CVE-2026-31450, ROOT-OS-DEBIAN-13-CVE-2026-31450, ROOT-OS-UBUNTU-2204-CVE-2026-31450, ROOT-OS-UBUNTU-2404-CVE-2026-31450, UBUNTU-CVE-2026-31450

## What is CVE-2026-31450?

CVE-2026-31450 is a high-severity vulnerability in Linux kernel, published on 22 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

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

ext4: publish jinode after initialization

ext4_inode_attach_jinode() publishes ei->jinode to concurrent users.
It used to set ei->jinode before jbd2_journal_init_jbd_inode(),
allowing a reader to observe a non-NULL jinode with i_vfs_inode
still unset.

The fast commit flush path can then pass this jinode to
jbd2_wait_inode_data(), which dereferences i_vfs_inode->i_mapping and
may crash.

Below is the crash I observe:
```
BUG: unable to handle page fault for address: 000000010beb47f4
PGD 110e51067 P4D 110e51067 PUD 0
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 1 UID: 0 PID: 4850 Comm: fc_fsync_bench_ Not tainted 6.18.0-00764-g795a690c06a5 #1 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.17.0-2-2 04/01/2014
RIP: 0010:xas_find_marked+0x3d/0x2e0
Code: e0 03 48 83 f8 02 0f 84 f0 01 00 00 48 8b 47 08 48 89 c3 48 39 c6 0f 82 fd 01 00 00 48 85 c9 74 3d 48 83 f9 03 77 63 4c 8b 0f <49> 8b 71 08 48 c7 47 18 00 00 00 00 48 89 f1 83 e1 03 48 83 f9 02
RSP: 0018:ffffbbee806e7bf0 EFLAGS: 00010246
RAX: 000000000010beb4 RBX: 000000000010beb4 RCX: 0000000000000003
RDX: 0000000000000001 RSI: 0000002000300000 RDI: ffffbbee806e7c10
RBP: 0000000000000001 R08: 0000002000300000 R09: 000000010beb47ec
R10: ffff9ea494590090 R11: 0000000000000000 R12: 0000002000300000
R13: ffffbbee806e7c90 R14: ffff9ea494513788 R15: ffffbbee806e7c88
FS: 00007fc2f9e3e6c0(0000) GS:ffff9ea6b1444000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000010beb47f4 CR3: 0000000119ac5000 CR4: 0000000000750ef0
PKRU: 55555554
Call Trace:
<TASK>
filemap_get_folios_tag+0x87/0x2a0
__filemap_fdatawait_range+0x5f/0xd0
? srso_alias_return_thunk+0x5/0xfbef5
? __schedule+0x3e7/0x10c0
? srso_alias_return_thunk+0x5/0xfbef5
? srso_alias_return_thunk+0x5/0xfbef5
? srso_alias_return_thunk+0x5/0xfbef5
? preempt_count_sub+0x5f/0x80
? srso_alias_return_thunk+0x5/0xfbef5
? cap_safe_nice+0x37/0x70
? srso_alias_return_thunk+0x5/0xfbef5
? preempt_count_sub+0x5f/0x80
? srso_alias_return_thunk+0x5/0xfbef5
filemap_fdatawait_range_keep_errors+0x12/0x40
ext4_fc_commit+0x697/0x8b0
? ext4_file_write_iter+0x64b/0x950
? srso_alias_return_thunk+0x5/0xfbef5
? preempt_count_sub+0x5f/0x80
? srso_alias_return_thunk+0x5/0xfbef5
? vfs_write+0x356/0x480
? srso_alias_return_thunk+0x5/0xfbef5
? preempt_count_sub+0x5f/0x80
ext4_sync_file+0xf7/0x370
do_fsync+0x3b/0x80
? syscall_trace_enter+0x108/0x1d0
__x64_sys_fdatasync+0x16/0x20
do_syscall_64+0x62/0x2c0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
...
```

Fix this by initializing the jbd2_inode first.
Use smp_wmb() and WRITE_ONCE() to publish ei->jinode after
initialization. Readers use READ_ONCE() to fetch the pointer.

Weakness: CWE-476 (NULL Pointer Dereference), CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-31450?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31450?

Apply the vendor's patch.

## Is CVE-2026-31450 being exploited?

There is no known exploitation of CVE-2026-31450 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-2026-31450 and fix it if it is affected.

What it is: CVE-2026-31450 is a high-severity vulnerability in Linux kernel, published on 22 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-31450 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-2026-31450/ (Markdown: https://insights.sbomify.com/CVE-2026-31450/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31450
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31450
- OSV: https://osv.dev/vulnerability/CVE-2026-31450

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31450/
Summaries are generated and may contain mistakes; the official description above is the record.