CVE-2025-40190
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-11-12

Last updated on: 2025-11-14

Assigner: kernel.org

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.
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Meta Information
Published
2025-11-12
Last Modified
2025-11-14
Generated
2026-05-07
AI Q&A
2025-11-13
EPSS Evaluated
2026-05-05
NVD
CVE-2025-40190
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-UNKNOWN
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AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability is in the Linux kernel's ext4 filesystem, where an extended attribute (EA) inode reference count can underflow during an xattr update. Specifically, the function ext4_xattr_inode_update_ref() may read a reference count that is already zero or negative and then decrement it further, causing an underflow. This leads to invalid reference counts and filesystem errors. The fix makes the system detect non-positive reference counts as on-disk corruption, report an error, and fail the operation instead of allowing the underflow.


How can this vulnerability impact me? :

This vulnerability can cause filesystem errors and corruption by allowing the reference count of an extended attribute inode to underflow. This may lead to orphaned inodes and cleanup issues, potentially causing data integrity problems or system instability when using the ext4 filesystem.


What immediate steps should I take to mitigate this vulnerability?

The vulnerability is resolved by updating the Linux kernel to a version that includes the fix for the ext4 EA inode refcount underflow issue. Immediate mitigation involves applying the kernel update that prevents the refcount underflow by treating non-positive refcounts as on-disk corruption and failing the operation safely.


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