# CVE-2024-49873: mm/filemap: fix filemap_get_folios_contig THP panic

> A local attacker can trigger a kernel panic via memfd_pin_folios with unaligned THP offsets, causing denial of service.

- **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 Oct 2024
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2024-49873, DEBIAN-CVE-2024-49873, GHSA-j2cc-c4fg-77cq, UBUNTU-CVE-2024-49873

## What is CVE-2024-49873?

CVE-2024-49873 is a medium-severity vulnerability in Linux kernel, published on 21 Oct 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:

mm/filemap: fix filemap_get_folios_contig THP panic

Patch series "memfd-pin huge page fixes".

Fix multiple bugs that occur when using memfd_pin_folios with hugetlb
pages and THP.  The hugetlb bugs only bite when the page is not yet
faulted in when memfd_pin_folios is called.  The THP bug bites when the
starting offset passed to memfd_pin_folios is not huge page aligned.  See
the commit messages for details.

This patch (of 5):

memfd_pin_folios on memory backed by THP panics if the requested start
offset is not huge page aligned:

BUG: kernel NULL pointer dereference, address: 0000000000000036
RIP: 0010:filemap_get_folios_contig+0xdf/0x290
RSP: 0018:ffffc9002092fbe8 EFLAGS: 00010202
RAX: 0000000000000002 RBX: 0000000000000002 RCX: 0000000000000002

The fault occurs here, because xas_load returns a folio with value 2:

    filemap_get_folios_contig()
        for (folio = xas_load(&xas); folio && xas.xa_index <= end;
                        folio = xas_next(&xas)) {
                ...
                if (!folio_try_get(folio))   <-- BOOM

"2" is an xarray sibling entry.  We get it because memfd_pin_folios does
not round the indices passed to filemap_get_folios_contig to huge page
boundaries for THP, so we load from the middle of a huge page range see a
sibling.  (It does round for hugetlbfs, at the is_file_hugepages test).

To fix, if the folio is a sibling, then return the next index as the
starting point for the next call to filemap_get_folios_contig.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2024-49873?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-49873?

Apply the vendor's patch.

## Is CVE-2024-49873 being exploited?

There is no known exploitation of CVE-2024-49873 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-2024-49873 and fix it if it is affected.

What it is: CVE-2024-49873 is a medium-severity vulnerability in Linux kernel, published on 21 Oct 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-2024-49873 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-2024-49873/ (Markdown: https://insights.sbomify.com/CVE-2024-49873/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-49873
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-49873
- OSV: https://osv.dev/vulnerability/CVE-2024-49873

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-49873/
Summaries are generated and may contain mistakes; the official description above is the record.