# CVE-2025-40190: ext4: guard against EA inode refcount underflow in xattr update

> A refcount underflow in the Linux kernel ext4 filesystem can cause errors and cleanup churn, potentially leading to denial of service.

- **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:** 5 Aug 2026
- **Also known as:** AZL-70091, BELL-CVE-2025-40190, DEBIAN-CVE-2025-40190, GHSA-j9x6-gmq6-xm5x, ROOT-OS-DEBIAN-11-CVE-2025-40190, ROOT-OS-DEBIAN-13-CVE-2025-40190, ROOT-OS-UBUNTU-2204-CVE-2025-40190, ROOT-OS-UBUNTU-2404-CVE-2025-40190, UBUNTU-CVE-2025-40190

## What is CVE-2025-40190?

CVE-2025-40190 is a high-severity 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: guard against EA inode refcount underflow in xattr update

syzkaller found a path where ext4_xattr_inode_update_ref() reads an EA
inode refcount that is already <= 0 and then applies ref_change (often
-1). That lets the refcount underflow and we proceed with a bogus value,
triggering errors like:

  EXT4-fs error: EA inode <n> ref underflow: ref_count=-1 ref_change=-1
  EXT4-fs warning: ea_inode dec ref err=-117

Make the invariant explicit: if the current refcount is non-positive,
treat this as on-disk corruption, emit ext4_error_inode(), and fail the
operation with -EFSCORRUPTED instead of updating the refcount. Delete the
WARN_ONCE() as negative refcounts are now impossible; keep error reporting
in ext4_error_inode().

This prevents the underflow and the follow-on orphan/cleanup churn.

## Which versions are affected by CVE-2025-40190?


## How do I fix CVE-2025-40190?

Apply the vendor's patch.

## Is CVE-2025-40190 being exploited?

There is no known exploitation of CVE-2025-40190 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40190 and fix it if it is affected.

What it is: CVE-2025-40190 is a high-severity 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-2025-40190 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-2025-40190/ (Markdown: https://insights.sbomify.com/CVE-2025-40190/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40190
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40190
- OSV: https://osv.dev/vulnerability/CVE-2025-40190

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40190/
Summaries are generated and may contain mistakes; the official description above is the record.