# CVE-2026-63917: ip6: vti: Use ip6_tnl.net in vti6_changelink().

> A use-after-free in the Linux kernel's IPv6 VTI tunnel handling allows local attackers to cause a system crash or potentially escalate privileges via network namespace manipulation.

- **Severity:** High 8.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/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:** 19 Jul 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-63917, DEBIAN-CVE-2026-63917, GHSA-225v-7w3r-pcq9, ROOT-OS-UBUNTU-2204-CVE-2026-63917, UBUNTU-CVE-2026-63917

## What is CVE-2026-63917?

CVE-2026-63917 is a high-severity use after free vulnerability in Linux, published on 19 Jul 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:

ip6: vti: Use ip6_tnl.net in vti6_changelink().

ip netns add ns1
ip netns add ns2
ip -n ns1 link add vti6_test type vti6 remote ::1 local ::2 key 7
ip -n ns1 link set vti6_test netns ns2
ip -n ns2 link set vti6_test type vti6 remote ::3 local ::4 key 9
ip netns del ns2
ip netns del ns1
[  132.495484] ------------[ cut here ]------------
[  132.497609] kernel BUG at net/core/dev.c:12376!

Commit 61220ab34948 ("vti6: Enable namespace changing") dropped
NETIF_F_NETNS_LOCAL from vti6 devices. A vti6 tunnel can then
move through IFLA_NET_NS_FD. After the move dev_net(dev) points
at the new netns while t->net stays at the creation netns.

vti6_changelink() and vti6_update() still use dev_net(dev) and
dev_net(t->dev). They unlink from one per netns hash and relink
into another. The creation netns is left with a stale entry.
cleanup_net() of that netns later walks freed memory.

Reachable from an unprivileged user namespace (unshare --user
--map-root-user --net). Cross tenant scope on container hosts.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-63917?


## How do I fix CVE-2026-63917?

Apply the vendor's patch.

## Is CVE-2026-63917 being exploited?

There is no known exploitation of CVE-2026-63917 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63917 and fix it if it is affected.

What it is: CVE-2026-63917 is a high-severity use after free vulnerability in Linux, published on 19 Jul 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-2026-63917 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-2026-63917/ (Markdown: https://insights.sbomify.com/CVE-2026-63917/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63917
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63917
- OSV: https://osv.dev/vulnerability/CVE-2026-63917

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63917/
Summaries are generated and may contain mistakes; the official description above is the record.