# CVE-2026-63815: f2fs: bound i_inline_xattr_size for non-inline-xattr inodes

> An attacker with a crafted filesystem image can trigger an out-of-bounds read in the Linux kernel f2fs driver, potentially leaking memory or causing a crash.

- **Severity:** High 8.4 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **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-2026-63815, DEBIAN-CVE-2026-63815, GHSA-7mq9-8547-cp53, ROOT-OS-DEBIAN-11-CVE-2026-63815, ROOT-OS-DEBIAN-12-CVE-2026-63815, ROOT-OS-UBUNTU-2204-CVE-2026-63815, UBUNTU-CVE-2026-63815

## What is CVE-2026-63815?

CVE-2026-63815 is a high-severity memory corruption 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: bound i_inline_xattr_size for non-inline-xattr inodes

When the flexible_inline_xattr feature is enabled, do_read_inode() loads
the on-disk i_inline_xattr_size unconditionally:

	if (f2fs_sb_has_flexible_inline_xattr(sbi))
		fi->i_inline_xattr_size = le16_to_cpu(ri->i_inline_xattr_size);

but sanity_check_inode() only range-checks it when the inode also has the
FI_INLINE_XATTR flag set.  An inode that carries an inline dentry or inline
data but not FI_INLINE_XATTR -- the normal layout for an inline
directory -- therefore keeps a fully attacker-controlled
i_inline_xattr_size from a crafted image.

get_inline_xattr_addrs() returns that value with no flag gating, so it
feeds the inode geometry:

	MAX_INLINE_DATA()  = 4 * (CUR_ADDRS_PER_INODE - i_inline_xattr_size - 1)
	NR_INLINE_DENTRY() = MAX_INLINE_DATA() * BITS_PER_BYTE / (...)
	addrs_per_page()   = CUR_ADDRS_PER_INODE - i_inline_xattr_size

A large i_inline_xattr_size drives MAX_INLINE_DATA() and NR_INLINE_DENTRY()
negative, so make_dentry_ptr_inline() sets d->max (int) to a negative
value.  The inline directory walk then compares an unsigned long bit_pos
against that negative d->max, which is promoted to a huge unsigned bound,
and reads far past the inline area:

	while (bit_pos < d->max)		/* fs/f2fs/dir.c */
		... test_bit_le(bit_pos, d->bitmap) / d->dentry[bit_pos] ...

Mounting a crafted image and reading such a directory triggers an
out-of-bounds read in f2fs_fill_dentries(); the same underflow also
corrupts ADDRS_PER_INODE for regular files.

Validate i_inline_xattr_size against MAX_INLINE_XATTR_SIZE whenever the
flexible_inline_xattr feature is enabled -- i.e. whenever the value is
loaded from disk and consumed -- and keep the lower MIN_INLINE_XATTR_SIZE
bound gated on inodes that actually carry an inline xattr, so legitimate
inodes with i_inline_xattr_size == 0 are still accepted.

## Which versions are affected by CVE-2026-63815?


## How do I fix CVE-2026-63815?

Apply the vendor's patch.

## Is CVE-2026-63815 being exploited?

There is no known exploitation of CVE-2026-63815 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63815 and fix it if it is affected.

What it is: CVE-2026-63815 is a high-severity memory corruption 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-2026-63815 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-2026-63815/ (Markdown: https://insights.sbomify.com/CVE-2026-63815/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63815
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63815
- OSV: https://osv.dev/vulnerability/CVE-2026-63815

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63815/
Summaries are generated and may contain mistakes; the official description above is the record.