# CVE-2026-98306: seg6: set IPSKB_L3SLAVE from IP6SKB_L3SLAVE on IPIP decapsulation

> Missing VRF flag in SRv6 decapsulation allows packets to bypass VRF isolation, potentially exposing data to sockets outside the intended network namespace.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-106272, BELL-CVE-2026-98306, DEBIAN-CVE-2026-98306, GHSA-8vq5-3gc9-33qh, UBUNTU-CVE-2026-98306

## What is CVE-2026-98306?

CVE-2026-98306 is a vulnerability in Linux, published on 6 Oct 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:

seg6: set IPSKB_L3SLAVE from IP6SKB_L3SLAVE on IPIP decapsulation

When an SRv6 packet arrives on an interface enslaved to a VRF,
vrf_ip6_rcv() sets IP6SKB_L3SLAVE in IP6CB, but decap_and_validate()
has never set IPSKB_L3SLAVE in IPCB. The bit stayed clear in the
common case, and with CONFIG_IPV6_MIP6 the leftover frag_max_size of
a reassembled outer packet could even set it, with no VRF involved.
Commit 44930446dde4 ("ipv6: seg6: clear IPv4 control block on IPIP
decapsulation") then made the unreliable bit reliably clear.

The effect of the missing flag is visible with End.DX4 when a
delivery to a local address of the node reaches the socket lookup.
For example, a UDP socket bound to the enslaved ingress interface
does not receive any of the decapsulated packets, while an unbound
socket outside the VRF does.
This contradicts Documentation/networking/vrf.rst: by default the
scope of an unbound UDP or TCP socket is limited to the default VRF.

Set IPSKB_L3SLAVE for IPv4 in decap_and_validate(), which already does
the same for IPv6. The socket lookup then matches the decapsulated
packet like any other packet received on that enslaved interface. Such
a packet matches an unbound UDP or TCP socket only when
udp_l3mdev_accept or tcp_l3mdev_accept is set.

## Which versions are affected by CVE-2026-98306?


## How do I fix CVE-2026-98306?

Apply the vendor's patch.

## Is CVE-2026-98306 being exploited?

There is no known exploitation of CVE-2026-98306 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98306 and fix it if it is affected.

What it is: CVE-2026-98306 is a vulnerability in Linux, published on 6 Oct 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-2026-98306 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-2026-98306/ (Markdown: https://insights.sbomify.com/CVE-2026-98306/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98306
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98306
- OSV: https://osv.dev/vulnerability/CVE-2026-98306

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98306/
Summaries are generated and may contain mistakes; the official description above is the record.