# CVE-2025-40167: ext4: detect invalid INLINE_DATA + EXTENTS flag combination

> A corrupted ext4 filesystem with invalid flags causes a kernel BUG_ON, leading to denial of service when mounted without a journal.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 12 Nov 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-69992, BELL-CVE-2025-40167, DEBIAN-CVE-2025-40167, GHSA-x383-8hmc-j634, ROOT-OS-DEBIAN-11-CVE-2025-40167, ROOT-OS-DEBIAN-13-CVE-2025-40167, ROOT-OS-UBUNTU-2404-CVE-2025-40167, UBUNTU-CVE-2025-40167

## What is CVE-2025-40167?

CVE-2025-40167 is a high-severity denial of service vulnerability in Linux, published on 12 Nov 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

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

ext4: detect invalid INLINE_DATA + EXTENTS flag combination

syzbot reported a BUG_ON in ext4_es_cache_extent() when opening a verity
file on a corrupted ext4 filesystem mounted without a journal.

The issue is that the filesystem has an inode with both the INLINE_DATA
and EXTENTS flags set:

    EXT4-fs error (device loop0): ext4_cache_extents:545: inode #15:
    comm syz.0.17: corrupted extent tree: lblk 0 < prev 66

Investigation revealed that the inode has both flags set:
    DEBUG: inode 15 - flag=1, i_inline_off=164, has_inline=1, extents_flag=1

This is an invalid combination since an inode should have either:
- INLINE_DATA: data stored directly in the inode
- EXTENTS: data stored in extent-mapped blocks

Having both flags causes ext4_has_inline_data() to return true, skipping
extent tree validation in __ext4_iget(). The unvalidated out-of-order
extents then trigger a BUG_ON in ext4_es_cache_extent() due to integer
underflow when calculating hole sizes.

Fix this by detecting this invalid flag combination early in ext4_iget()
and rejecting the corrupted inode.

## Which versions are affected by CVE-2025-40167?


## How do I fix CVE-2025-40167?

Apply the vendor's patch.

## Is CVE-2025-40167 being exploited?

There is no known exploitation of CVE-2025-40167 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40167 and fix it if it is affected.

What it is: CVE-2025-40167 is a high-severity denial of service vulnerability in Linux, published on 12 Nov 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2025-40167 in the wild and no public exploit code.

Affected product: Linux. 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-2025-40167/ (Markdown: https://insights.sbomify.com/CVE-2025-40167/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40167
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40167
- OSV: https://osv.dev/vulnerability/CVE-2025-40167

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40167/
Summaries are generated and may contain mistakes; the official description above is the record.