CVE-2025-68796 f2fs: fix to avoid updating zero-sized extent in extent cache
A local attacker can trigger a kernel bug in the F2FS filesystem by causing a zero-sized extent update, leading to a system crash.
- 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-2025-68796?
CVE-2025-68796 is a vulnerability in Linux, published on 13 Jan 2026. 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:
f2fs: fix to avoid updating zero-sized extent in extent cache
As syzbot reported:
F2FS-fs (loop0): __update_extent_tree_range: extent len is zero, type: 0, extent [0, 0, 0], age [0, 0] ------------[ cut here ]------------ kernel BUG at fs/f2fs/extent_cache.c:678! Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI CPU: 0 UID: 0 PID: 5336 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:__update_extent_tree_range+0x13bc/0x1500 fs/f2fs/extent_cache.c:678 Call Trace: <TASK> f2fs_update_read_extent_cache_range+0x192/0x3e0 fs/f2fs/extent_cache.c:1085 f2fs_do_zero_range fs/f2fs/file.c:1657 [inline] f2fs_zero_range+0x10c1/0x1580 fs/f2fs/file.c:1737 f2fs_fallocate+0x583/0x990 fs/f2fs/file.c:2030 vfs_fallocate+0x669/0x7e0 fs/open.c:342 ioctl_preallocate fs/ioctl.c:289 [inline] file_ioctl+0x611/0x780 fs/ioctl.c:-1 do_vfs_ioctl+0xb33/0x1430 fs/ioctl.c:576 __do_sys_ioctl fs/ioctl.c:595 [inline] __se_sys_ioctl+0x82/0x170 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f07bc58eec9
In error path of f2fs_zero_range(), it may add a zero-sized extent into extent cache, it should be avoided.
Which versions are affected by CVE-2025-68796?
How do I fix CVE-2025-68796?
Apply the vendor's patch.
Is CVE-2025-68796 being exploited?
There is no known exploitation of CVE-2025-68796 in the wild and no public exploit code.
Sources
Also known as AZL-74306, BELL-CVE-2025-68796, DEBIAN-CVE-2025-68796, GHSA-x84x-5w8g-xr7g, ROOT-OS-DEBIAN-11-CVE-2025-68796, ROOT-OS-DEBIAN-12-CVE-2025-68796 and 4 more.