# CVE-2024-36966: erofs: reliably distinguish block based and fscache mode

> A logic error in the Linux kernel EROFS filesystem can cause a kernel warning and potential denial of service when mounting in block device mode with on-demand features enabled.

- **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:** 8 Jun 2024
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2024-36966, DEBIAN-CVE-2024-36966, GHSA-9644-wv3x-7gcf, ROOT-OS-UBUNTU-2204-CVE-2024-36966, UBUNTU-CVE-2024-36966

## What is CVE-2024-36966?

CVE-2024-36966 is a medium-severity vulnerability in Linux kernel, published on 8 Jun 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:

erofs: reliably distinguish block based and fscache mode

When erofs_kill_sb() is called in block dev based mode, s_bdev may not
have been initialised yet, and if CONFIG_EROFS_FS_ONDEMAND is enabled,
it will be mistaken for fscache mode, and then attempt to free an anon_dev
that has never been allocated, triggering the following warning:

============================================
ida_free called for id=0 which is not allocated.
WARNING: CPU: 14 PID: 926 at lib/idr.c:525 ida_free+0x134/0x140
Modules linked in:
CPU: 14 PID: 926 Comm: mount Not tainted 6.9.0-rc3-dirty #630
RIP: 0010:ida_free+0x134/0x140
Call Trace:
 <TASK>
 erofs_kill_sb+0x81/0x90
 deactivate_locked_super+0x35/0x80
 get_tree_bdev+0x136/0x1e0
 vfs_get_tree+0x2c/0xf0
 do_new_mount+0x190/0x2f0
 [...]
============================================

Now when erofs_kill_sb() is called, erofs_sb_info must have been
initialised, so use sbi->fsid to distinguish between the two modes.

Weakness: CWE-824 (Access of Uninitialized Pointer)

## Which versions are affected by CVE-2024-36966?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-36966?

Apply the vendor's patch.

## Is CVE-2024-36966 being exploited?

There is no known exploitation of CVE-2024-36966 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-2024-36966 and fix it if it is affected.

What it is: CVE-2024-36966 is a medium-severity vulnerability in Linux kernel, published on 8 Jun 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-2024-36966 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-2024-36966/ (Markdown: https://insights.sbomify.com/CVE-2024-36966/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-36966
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-36966
- OSV: https://osv.dev/vulnerability/CVE-2024-36966

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-36966/
Summaries are generated and may contain mistakes; the official description above is the record.