CVE-2023-54021 ext4: set goal start correctly in ext4_mb_normalize_request
A local attacker can trigger a kernel BUG_ON crash in the ext4 filesystem via an integer underflow, causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2023-54021?
CVE-2023-54021 is a vulnerability in Linux, published on 24 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ext4: set goal start correctly in ext4_mb_normalize_request
We need to set ac_g_ex to notify the goal start used in ext4_mb_find_by_goal. Set ac_g_ex instead of ac_f_ex in ext4_mb_normalize_request. Besides we should assure goal start is in range [first_data_block, blocks_count) as ext4_mb_initialize_context does.
[ Added a check to make sure size is less than ar->pright; otherwise we could end up passing an underflowed value of ar->pright - size to ext4_get_group_no_and_offset(), which will trigger a BUG_ON later on. - TYT ]
Which versions are affected by CVE-2023-54021?
How do I fix CVE-2023-54021?
Apply the vendor's patch.
Is CVE-2023-54021 being exploited?
There is no known exploitation of CVE-2023-54021 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2023-54021, DEBIAN-CVE-2023-54021, GHSA-xwm6-35hh-fmxm, UBUNTU-CVE-2023-54021.