# CVE-2026-53070: sctp: disable BH before calling udp_tunnel_xmit_skb()

> A race condition in Linux kernel SCTP UDP tunneling causes packet drops and performance degradation when SCTP over UDP is enabled.

- **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:** 24 Jun 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-90471, BELL-CVE-2026-53070, DEBIAN-CVE-2026-53070, GHSA-q4jf-gp35-367g, ROOT-OS-DEBIAN-12-CVE-2026-53070, ROOT-OS-DEBIAN-13-CVE-2026-53070, ROOT-OS-UBUNTU-2204-CVE-2026-53070, ROOT-OS-UBUNTU-2404-CVE-2026-53070, UBUNTU-CVE-2026-53070

## What is CVE-2026-53070?

CVE-2026-53070 is a high-severity vulnerability in Linux kernel, published on 24 Jun 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:

sctp: disable BH before calling udp_tunnel_xmit_skb()

udp_tunnel_xmit_skb() / udp_tunnel6_xmit_skb() are expected to run with
BH disabled.  After commit 6f1a9140ecda ("add xmit recursion limit to
tunnel xmit functions"), on the path:

  udp(6)_tunnel_xmit_skb() -> ip(6)tunnel_xmit()

dev_xmit_recursion_inc()/dec() must stay balanced on the same CPU.

Without local_bh_disable(), the context may move between CPUs, which can
break the inc/dec pairing. This may lead to incorrect recursion level
detection and cause packets to be dropped in ip(6)_tunnel_xmit() or
__dev_queue_xmit().

Fix it by disabling BH around both IPv4 and IPv6 SCTP UDP xmit paths.

In my testing, after enabling the SCTP over UDP:

  # ip net exec ha sysctl -w net.sctp.udp_port=9899
  # ip net exec ha sysctl -w net.sctp.encap_port=9899
  # ip net exec hb sysctl -w net.sctp.udp_port=9899
  # ip net exec hb sysctl -w net.sctp.encap_port=9899

  # ip net exec ha iperf3 -s

- without this patch:

  # ip net exec hb iperf3 -c 192.168.0.1 --sctp
  [  5]   0.00-10.00  sec  37.2 MBytes  31.2 Mbits/sec  sender
  [  5]   0.00-10.00  sec  37.1 MBytes  31.1 Mbits/sec  receiver

- with this patch:

  # ip net exec hb iperf3 -c 192.168.0.1 --sctp
  [  5]   0.00-10.00  sec  3.14 GBytes  2.69 Gbits/sec  sender
  [  5]   0.00-10.00  sec  3.14 GBytes  2.69 Gbits/sec  receiver

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-53070?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-53070?

Apply the vendor's patch.

## Is CVE-2026-53070 being exploited?

There is no known exploitation of CVE-2026-53070 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-2026-53070 and fix it if it is affected.

What it is: CVE-2026-53070 is a high-severity vulnerability in Linux kernel, published on 24 Jun 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-2026-53070 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-2026-53070/ (Markdown: https://insights.sbomify.com/CVE-2026-53070/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53070
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53070
- OSV: https://osv.dev/vulnerability/CVE-2026-53070

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53070/
Summaries are generated and may contain mistakes; the official description above is the record.