CVE-2026-31448 ext4: avoid infinite loops caused by residual data
A flaw in the Linux kernel ext4 filesystem allows local attackers to cause a denial of service via infinite loops during directory creation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-31448?
CVE-2026-31448 is a critical denial of service vulnerability in Linux kernel, published on 22 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ext4: avoid infinite loops caused by residual data
On the mkdir/mknod path, when mapping logical blocks to physical blocks, if inserting a new extent into the extent tree fails (in this example, because the file system disabled the huge file feature when marking the inode as dirty), ext4_ext_map_blocks() only calls ext4_free_blocks() to reclaim the physical block without deleting the corresponding data in the extent tree. This causes subsequent mkdir operations to reference the previously reclaimed physical block number again, even though this physical block is already being used by the xattr block. Therefore, a situation arises where both the directory and xattr are using the same buffer head block in memory simultaneously.
The above causes ext4_xattr_block_set() to enter an infinite loop about "inserted" and cannot release the inode lock, ultimately leading to the 143s blocking problem mentioned in [1].
If the metadata is corrupted, then trying to remove some extent space can do even more harm. Also in case EXT4_GET_BLOCKS_DELALLOC_RESERVE was passed, remove space wrongly update quota information. Jan Kara suggests distinguishing between two cases:
1) The error is ENOSPC or EDQUOT - in this case the filesystem is fully consistent and we must maintain its consistency including all the accounting. However these errors can happen only early before we've inserted the extent into the extent tree. So current code works correctly for this case.
2) Some other error - this means metadata is corrupted. We should strive to do as few modifications as possible to limit damage. So I'd just skip freeing of allocated blocks.
[1] INFO: task syz.0.17:5995 blocked for more than 143 seconds. Call Trace: inode_lock_nested include/linux/fs.h:1073 [inline] __start_dirop fs/namei.c:2923 [inline] start_dirop fs/namei.c:2934 [inline]
Weakness: CWE-835
Which versions are affected by CVE-2026-31448?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31448?
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-2026-31448 being exploited?
There is no known exploitation of CVE-2026-31448 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-83309, BELL-CVE-2026-31448, DEBIAN-CVE-2026-31448, GHSA-m6jj-c3pv-cg65, ROOT-OS-DEBIAN-11-CVE-2026-31448, ROOT-OS-DEBIAN-12-CVE-2026-31448 and 4 more.