# CVE-2026-89789: gtp: add synchronize_net() in gtp_newlink() error path to prevent use-after-free

> A use-after-free in the Linux kernel GTP module allows attackers to cause denial of service or execute code via concurrent network processing.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101405, BELL-CVE-2026-89789, DEBIAN-CVE-2026-89789, GHSA-h6q8-7j67-4q68, UBUNTU-CVE-2026-89789

## What is CVE-2026-89789?

CVE-2026-89789 is a high-severity use after free vulnerability in Linux, published on 16 Sep 2026. 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:

gtp: add synchronize_net() in gtp_newlink() error path to prevent use-after-free

gtp_newlink()'s error path frees tid_hash and addr_hash without
waiting for an RCU grace period after clearing sk_user_data. A
concurrent gtp_encap_recv() in softirq may still hold the gtp_dev
pointer obtained via rcu_dereference_sk_user_data() and access the
freed memory.

  BUG: KASAN: slab-use-after-free in gtp0_pdp_find+0x1f6/0x200 (gtp.c:152)
  Call Trace:
   <IRQ>
   gtp0_pdp_find+0x1f6/0x200
   gtp_encap_recv+0x527/0x24b0
   udp_queue_rcv_one_skb+0x75f/0xc10

Add synchronize_net() before the kfree calls in out_hashtable, which
covers all error paths from both gtp_encap_enable() and
gtp_create_sockets().

## Which versions are affected by CVE-2026-89789?


## How do I fix CVE-2026-89789?

Apply the vendor's patch.

## Is CVE-2026-89789 being exploited?

There is no known exploitation of CVE-2026-89789 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89789 and fix it if it is affected.

What it is: CVE-2026-89789 is a high-severity use after free vulnerability in Linux, published on 16 Sep 2026. 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-2026-89789 in the wild and no public exploit code.

Affected product: Linux. 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-2026-89789/ (Markdown: https://insights.sbomify.com/CVE-2026-89789/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89789
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89789
- OSV: https://osv.dev/vulnerability/CVE-2026-89789

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89789/
Summaries are generated and may contain mistakes; the official description above is the record.