# CVE-2026-98802: seg6: ensure packet data is writable before modifying SRH and IPv6 DA

> An attacker can read or modify shared packet data in the Linux kernel via Segment Routing, potentially leaking information or corrupting network traffic.

- **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:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-109146, BELL-CVE-2026-98802, DEBIAN-CVE-2026-98802, GHSA-mq8p-h4gv-vq5x, UBUNTU-CVE-2026-98802

## What is CVE-2026-98802?

CVE-2026-98802 is a memory corruption vulnerability in Linux, published on 18 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: ensure packet data is writable before modifying SRH and IPv6 DA

advance_nextseg() modifies the SRH Segments Left field and the IPv6
destination address without ensuring the packet data is writable.
seg6_next_csid_advance_arg() has the same problem when it advances the
NEXT-C-SID argument in the destination address.

The skb may be cloned, for example by an AF_PACKET socket receiving on
the ingress device. advance_nextseg() and seg6_next_csid_advance_arg()
then write into the packet data shared with the clone. A read from that
socket can return the modified packet instead of the received one. The
simplified path below shows this for advance_nextseg():

__netif_receive_skb_one_core
  __netif_receive_skb_core
    deliver_skb               [orig: users=2, cloned=0]
      packet_rcv
        skb_clone             clone queued to the AF_PACKET socket
        consume_skb(orig)     [orig: users=1, cloned=1]
  ipv6_rcv
    ip6_rcv_core              skb_share_check: no-op [orig: users=1]
    [...]
      input_action_end_core
        advance_nextseg       writes into the data shared with the clone

Call skb_ensure_writable() in advance_nextseg() and in
seg6_next_csid_advance_arg() before they modify the packet data.
skb_ensure_writable() may reallocate skb->head, which invalidates the
pointers into the packet data taken before the call.
advance_nextseg() now returns a valid SRH pointer, or NULL if
skb_ensure_writable() fails.
seg6_next_csid_advance_arg() takes the pointer to the destination
address from the skb after skb_ensure_writable().
On failure, the callers drop the packet with SKB_DROP_REASON_NOMEM.

## Which versions are affected by CVE-2026-98802?


## How do I fix CVE-2026-98802?

Apply the vendor's patch.

## Is CVE-2026-98802 being exploited?

There is no known exploitation of CVE-2026-98802 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98802 and fix it if it is affected.

What it is: CVE-2026-98802 is a memory corruption vulnerability in Linux, published on 18 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-2026-98802 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-2026-98802/ (Markdown: https://insights.sbomify.com/CVE-2026-98802/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98802
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98802
- OSV: https://osv.dev/vulnerability/CVE-2026-98802

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98802/
Summaries are generated and may contain mistakes; the official description above is the record.