# CVE-2026-63816: f2fs: atomic: fix UAF issue on f2fs_inode_info.atomic_inode

> A use-after-free vulnerability in the Linux kernel's f2fs atomic file handling allows attackers to cause a system crash or potentially execute arbitrary code.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** 19 Jul 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-63816, DEBIAN-CVE-2026-63816, GHSA-gp48-qw68-qgg5, ROOT-OS-DEBIAN-12-CVE-2026-63816, UBUNTU-CVE-2026-63816

## What is CVE-2026-63816?

CVE-2026-63816 is a high-severity use after free vulnerability in Linux, published on 19 Jul 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: atomic: fix UAF issue on f2fs_inode_info.atomic_inode

- ioctl(F2FS_IOC_GARBAGE_COLLECT_RANGE)		- shrink
 - f2fs_gc
  - gc_data_segment
   - ra_data_block(cow_inode)
    - mapping = F2FS_I(inode)->atomic_inode->i_mapping
    : f2fs_is_cow_file(cow_inode) is true
						 - f2fs_evict_inode(atomic_inode)
						  - clear_inode_flag(fi->cow_inode, FI_COW_FILE)
						  - F2FS_I(fi->cow_inode)->atomic_inode = NULL
						  ...
						  - truncate_inode_pages_final(atomic_inode)
    - f2fs_grab_cache_folio(mapping)
    : create folio in atomic_inode->mapping
						  - clear_inode(atomic_inode)
						   - BUG_ON(atomic_inode->i_data.nrpages)

We need to add a reference on fi->atomic_inode before using its mapping
field during garbage collection, otherwise, it will cause UAF issue.

## Which versions are affected by CVE-2026-63816?


## How do I fix CVE-2026-63816?

Apply the vendor's patch.

## Is CVE-2026-63816 being exploited?

There is no known exploitation of CVE-2026-63816 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63816 and fix it if it is affected.

What it is: CVE-2026-63816 is a high-severity use after free vulnerability in Linux, published on 19 Jul 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-2026-63816 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-2026-63816/ (Markdown: https://insights.sbomify.com/CVE-2026-63816/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63816
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63816
- OSV: https://osv.dev/vulnerability/CVE-2026-63816

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63816/
Summaries are generated and may contain mistakes; the official description above is the record.