# CVE-2025-40246: xfs: fix out of bounds memory read error in symlink repair

> A local attacker with high privileges can trigger an out-of-bounds memory read in the XFS symlink repair code, potentially causing a system crash or leaking kernel memory.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Dec 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-40246, DEBIAN-CVE-2025-40246, GHSA-x6g9-37j8-7qh9, ROOT-OS-DEBIAN-13-CVE-2025-40246, UBUNTU-CVE-2025-40246

## What is CVE-2025-40246?

CVE-2025-40246 is a memory corruption vulnerability in Linux, published on 4 Dec 2025. 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:

xfs: fix out of bounds memory read error in symlink repair

xfs/286 produced this report on my test fleet:

 ==================================================================
 BUG: KFENCE: out-of-bounds read in memcpy_orig+0x54/0x110

 Out-of-bounds read at 0xffff88843fe9e038 (184B right of kfence-#184):
  memcpy_orig+0x54/0x110
  xrep_symlink_salvage_inline+0xb3/0xf0 [xfs]
  xrep_symlink_salvage+0x100/0x110 [xfs]
  xrep_symlink+0x2e/0x80 [xfs]
  xrep_attempt+0x61/0x1f0 [xfs]
  xfs_scrub_metadata+0x34f/0x5c0 [xfs]
  xfs_ioc_scrubv_metadata+0x387/0x560 [xfs]
  xfs_file_ioctl+0xe23/0x10e0 [xfs]
  __x64_sys_ioctl+0x76/0xc0
  do_syscall_64+0x4e/0x1e0
  entry_SYSCALL_64_after_hwframe+0x4b/0x53

 kfence-#184: 0xffff88843fe9df80-0xffff88843fe9dfea, size=107, cache=kmalloc-128

 allocated by task 3470 on cpu 1 at 263329.131592s (192823.508886s ago):
  xfs_init_local_fork+0x79/0xe0 [xfs]
  xfs_iformat_local+0xa4/0x170 [xfs]
  xfs_iformat_data_fork+0x148/0x180 [xfs]
  xfs_inode_from_disk+0x2cd/0x480 [xfs]
  xfs_iget+0x450/0xd60 [xfs]
  xfs_bulkstat_one_int+0x6b/0x510 [xfs]
  xfs_bulkstat_iwalk+0x1e/0x30 [xfs]
  xfs_iwalk_ag_recs+0xdf/0x150 [xfs]
  xfs_iwalk_run_callbacks+0xb9/0x190 [xfs]
  xfs_iwalk_ag+0x1dc/0x2f0 [xfs]
  xfs_iwalk_args.constprop.0+0x6a/0x120 [xfs]
  xfs_iwalk+0xa4/0xd0 [xfs]
  xfs_bulkstat+0xfa/0x170 [xfs]
  xfs_ioc_fsbulkstat.isra.0+0x13a/0x230 [xfs]
  xfs_file_ioctl+0xbf2/0x10e0 [xfs]
  __x64_sys_ioctl+0x76/0xc0
  do_syscall_64+0x4e/0x1e0
  entry_SYSCALL_64_after_hwframe+0x4b/0x53

 CPU: 1 UID: 0 PID: 1300113 Comm: xfs_scrub Not tainted 6.18.0-rc4-djwx #rc4 PREEMPT(lazy)  3d744dd94e92690f00a04398d2bd8631dcef1954
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-4.module+el8.8.0+21164+ed375313 04/01/2014
 ==================================================================

On further analysis, I realized that the second parameter to min() is
not correct.  xfs_ifork::if_bytes is the size of the xfs_ifork::if_data
buffer.  if_bytes can be smaller than the data fork size because:

(a) the forkoff code tries to keep the data area as large as possible
(b) for symbolic links, if_bytes is the ondisk file size + 1
(c) forkoff is always a multiple of 8.

Case in point: for a single-byte symlink target, forkoff will be
8 but the buffer will only be 2 bytes long.

In other words, the logic here is wrong and we walk off the end of the
incore buffer.  Fix that.

## Which versions are affected by CVE-2025-40246?


## How do I fix CVE-2025-40246?

Apply the vendor's patch.

## Is CVE-2025-40246 being exploited?

There is no known exploitation of CVE-2025-40246 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40246 and fix it if it is affected.

What it is: CVE-2025-40246 is a memory corruption vulnerability in Linux, published on 4 Dec 2025. 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-2025-40246 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-2025-40246/ (Markdown: https://insights.sbomify.com/CVE-2025-40246/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40246
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40246
- OSV: https://osv.dev/vulnerability/CVE-2025-40246

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40246/
Summaries are generated and may contain mistakes; the official description above is the record.