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.
- 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
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.
Sources
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 and 3 more.