# CVE-2021-47406: ext4: add error checking to ext4_ext_replay_set_iblocks()

> A corrupted filesystem can cause an infinite loop in the Linux kernel ext4 fast commit replay, leading to a system hang.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 21 May 2024
- **Updated:** 11 May 2026
- **Also known as:** DEBIAN-CVE-2021-47406, GHSA-95jj-pjw6-q9fr, UBUNTU-CVE-2021-47406

## What is CVE-2021-47406?

CVE-2021-47406 is a medium-severity denial of service vulnerability in Linux kernel, published on 21 May 2024. 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:

ext4: add error checking to ext4_ext_replay_set_iblocks()

If the call to ext4_map_blocks() fails due to an corrupted file
system, ext4_ext_replay_set_iblocks() can get stuck in an infinite
loop.  This could be reproduced by running generic/526 with a file
system that has inline_data and fast_commit enabled.  The system will
repeatedly log to the console:

EXT4-fs warning (device dm-3): ext4_block_to_path:105: block 1074800922 > max in inode 131076

and the stack that it gets stuck in is:

   ext4_block_to_path+0xe3/0x130
   ext4_ind_map_blocks+0x93/0x690
   ext4_map_blocks+0x100/0x660
   skip_hole+0x47/0x70
   ext4_ext_replay_set_iblocks+0x223/0x440
   ext4_fc_replay_inode+0x29e/0x3b0
   ext4_fc_replay+0x278/0x550
   do_one_pass+0x646/0xc10
   jbd2_journal_recover+0x14a/0x270
   jbd2_journal_load+0xc4/0x150
   ext4_load_journal+0x1f3/0x490
   ext4_fill_super+0x22d4/0x2c00

With this patch, generic/526 still fails, but system is no longer
locking up in a tight loop.  It's likely the root casue is that
fast_commit replay is corrupting file systems with inline_data, and we
probably need to add better error handling in the fast commit replay
code path beyond what is done here, which essentially just breaks the
infinite loop without reporting the to the higher levels of the code.

Weakness: CWE-835 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2021-47406?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47406?

Apply the vendor's patch.

## Is CVE-2021-47406 being exploited?

There is no known exploitation of CVE-2021-47406 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-47406 and fix it if it is affected.

What it is: CVE-2021-47406 is a medium-severity denial of service vulnerability in Linux kernel, published on 21 May 2024. 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-2021-47406 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2021-47406/ (Markdown: https://insights.sbomify.com/CVE-2021-47406/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47406
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47406
- OSV: https://osv.dev/vulnerability/CVE-2021-47406

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47406/
Summaries are generated and may contain mistakes; the official description above is the record.