# CVE-2026-43254: ovpn: tcp - fix packet extraction from stream

> An integer overflow in the Linux kernel's OpenVPN TCP module causes packet drops, leading to denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 May 2026
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2026-43254, DEBIAN-CVE-2026-43254, GHSA-wp3j-57qp-wwvh, UBUNTU-CVE-2026-43254

## What is CVE-2026-43254?

CVE-2026-43254 is a high-severity vulnerability in Linux kernel, published on 6 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ovpn: tcp - fix packet extraction from stream

When processing TCP stream data in ovpn_tcp_recv, we receive large
cloned skbs from __strp_rcv that may contain multiple coalesced packets.
The current implementation has two bugs:

1. Header offset overflow: Using pskb_pull with large offsets on
   coalesced skbs causes skb->data - skb->head to exceed the u16 storage
   of skb->network_header. This causes skb_reset_network_header to fail
   on the inner decapsulated packet, resulting in packet drops.

2. Unaligned protocol headers: Extracting packets from arbitrary
   positions within the coalesced TCP stream provides no alignment
   guarantees for the packet data causing performance penalties on
   architectures without efficient unaligned access. Additionally,
   openvpn's 2-byte length prefix on TCP packets causes the subsequent
   4-byte opcode and packet ID fields to be inherently misaligned.

Fix both issues by allocating a new skb for each openvpn packet and
using skb_copy_bits to extract only the packet content into the new
buffer, skipping the 2-byte length prefix. Also, check the length before
invoking the function that performs the allocation to avoid creating an
invalid skb.

If the packet has to be forwarded to userspace the 2-byte prefix can be
pushed to the head safely, without misalignment.

As a side effect, this approach also avoids the expensive linearization
that pskb_pull triggers on cloned skbs with page fragments. In testing,
this resulted in TCP throughput improvements of up to 74%.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-43254?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43254?

Apply the vendor's patch.

## Is CVE-2026-43254 being exploited?

There is no known exploitation of CVE-2026-43254 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-2026-43254 and fix it if it is affected.

What it is: CVE-2026-43254 is a high-severity vulnerability in Linux kernel, published on 6 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-43254 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-2026-43254/ (Markdown: https://insights.sbomify.com/CVE-2026-43254/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43254
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43254
- OSV: https://osv.dev/vulnerability/CVE-2026-43254

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43254/
Summaries are generated and may contain mistakes; the official description above is the record.