# 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.

- **Severity:** Not scored
- **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:** Yes
- **Published:** 13 Jan 2026
- **Updated:** 11 May 2026
- **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, ROOT-OS-DEBIAN-13-CVE-2025-68796, ROOT-OS-UBUNTU-2204-CVE-2025-68796, ROOT-OS-UBUNTU-2404-CVE-2025-68796, UBUNTU-CVE-2025-68796

## 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-68796 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2025-68796 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-68796/ (Markdown: https://insights.sbomify.com/CVE-2025-68796/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-68796
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-68796
- OSV: https://osv.dev/vulnerability/CVE-2025-68796

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-68796/
Summaries are generated and may contain mistakes; the official description above is the record.