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.
- 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-2025-40167?
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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-40167 being exploited?
There is no known exploitation of CVE-2025-40167 in the wild and no public exploit code.
Sources
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 and 2 more.