# CVE-2023-52527: ipv4, ipv6: Fix handling of transhdrlen in __ip{,6}_append_data()

> A flaw in Linux kernel IPv4/IPv6 packet handling allows triggering a kernel warning and potential denial of service via specific socket operations.

- **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:** 2 Mar 2024
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2023-52527, DEBIAN-CVE-2023-52527, GHSA-j6qg-38wf-82gm, UBUNTU-CVE-2023-52527

## What is CVE-2023-52527?

CVE-2023-52527 is a medium-severity denial of service vulnerability in Linux kernel, published on 2 Mar 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:

ipv4, ipv6: Fix handling of transhdrlen in __ip{,6}_append_data()

Including the transhdrlen in length is a problem when the packet is
partially filled (e.g. something like send(MSG_MORE) happened previously)
when appending to an IPv4 or IPv6 packet as we don't want to repeat the
transport header or account for it twice.  This can happen under some
circumstances, such as splicing into an L2TP socket.

The symptom observed is a warning in __ip6_append_data():

    WARNING: CPU: 1 PID: 5042 at net/ipv6/ip6_output.c:1800 __ip6_append_data.isra.0+0x1be8/0x47f0 net/ipv6/ip6_output.c:1800

that occurs when MSG_SPLICE_PAGES is used to append more data to an already
partially occupied skbuff.  The warning occurs when 'copy' is larger than
the amount of data in the message iterator.  This is because the requested
length includes the transport header length when it shouldn't.  This can be
triggered by, for example:

        sfd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_L2TP);
        bind(sfd, ...); // ::1
        connect(sfd, ...); // ::1 port 7
        send(sfd, buffer, 4100, MSG_MORE);
        sendfile(sfd, dfd, NULL, 1024);

Fix this by only adding transhdrlen into the length if the write queue is
empty in l2tp_ip6_sendmsg(), analogously to how UDP does things.

l2tp_ip_sendmsg() looks like it won't suffer from this problem as it builds
the UDP packet itself.

## Which versions are affected by CVE-2023-52527?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2023-52527?

Apply the vendor's patch.

## Is CVE-2023-52527 being exploited?

There is no known exploitation of CVE-2023-52527 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-2023-52527 and fix it if it is affected.

What it is: CVE-2023-52527 is a medium-severity denial of service vulnerability in Linux kernel, published on 2 Mar 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-2023-52527 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-2023-52527/ (Markdown: https://insights.sbomify.com/CVE-2023-52527/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-52527
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-52527
- OSV: https://osv.dev/vulnerability/CVE-2023-52527

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-52527/
Summaries are generated and may contain mistakes; the official description above is the record.