CVE-2026-89786 ext4: fix out-of-bounds read in ext4_read_inline_dir()
A local attacker can trigger an out-of-bounds read in the ext4 filesystem, potentially leaking kernel memory or causing a system crash.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89786?
CVE-2026-89786 is a critical memory corruption vulnerability in Linux, published on 16 Sep 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: fix out-of-bounds read in ext4_read_inline_dir()
ext4_read_inline_dir() can read a dirent header past the end of its inline buffer, triggering a slab-out-of-bounds read during getdents64():
BUG: KASAN: slab-out-of-bounds in __ext4_check_dir_entry Read of size 2 at addr ffff88800f3dd23c by task exploit/148 ... __ext4_check_dir_entry ext4_read_inline_dir iterate_dir
The dirent payload lives in a buffer of exactly inline_size bytes:
dir_buf = kmalloc(inline_size, GFP_NOFS);
but iteration runs in a position space extra_offset bytes larger (extra_size = extra_offset + inline_size) so the synthetic "." and ".." land at their block-dir offsets. A dirent is formed at "dir_buf + pos - extra_offset", yet the ext4_check_dir_entry() length argument uses the larger extra_size. A position whose dirent header would extend past extra_size is therefore accepted, and the rescan loop's rec_len probe and ext4_check_dir_entry() dereference de->rec_len before the entry is rejected.
Reject a position whose minimum-size dirent header would not fit within extra_size before forming de, in both the rescan and main loops, and pass inline_size rather than extra_size to ext4_check_dir_entry() so the length check matches the physical buffer.
Which versions are affected by CVE-2026-89786?
How do I fix CVE-2026-89786?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-89786 being exploited?
There is no known exploitation of CVE-2026-89786 in the wild and no public exploit code.
Sources
Also known as AZL-101309, BELL-CVE-2026-89786, DEBIAN-CVE-2026-89786, GHSA-7xr2-rx94-5f89, UBUNTU-CVE-2026-89786.