# CVE-2026-98371: xfrm: iptfs: fix runt reassembly panic from short inner tot_len

> An attacker can cause a kernel panic via crafted IPTFS packets, leading to denial of service on Linux systems with IPTFS enabled.

- **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:** BELL-CVE-2026-98371, DEBIAN-CVE-2026-98371, GHSA-jfv3-vhc3-4xwh, UBUNTU-CVE-2026-98371

## What is CVE-2026-98371?

CVE-2026-98371 is a denial of service 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:

xfrm: iptfs: fix runt reassembly panic from short inner tot_len

When the start of an inner packet is split across two outer packets
such that fewer than 4 bytes land at the end of the first one,
__input_process_payload() saves those bytes as a runt and skips the
iplen/iphlen validation performed for in-place packets. When the
continuation packet arrives, iptfs_reassem_cont() only requires the
declared inner length to be >= sizeof(ra_runt) (6) before allocating
the reassembly skb with that attacker-controlled length.

However, __iptfs_iphlen() always returns the fixed minimum IP header
size (20 for IPv4, 40 for IPv6), so for an inner IPv4 tot_len in
[6, 19] the header-completion copy writes past the declared packet
length, and the subsequent "ipremain -= copylen" underflows to ~4GB,
leaving the payload copy length bounded only by blkoff (up to 64KB).
At runtime the skb_put() tailroom check turns this into
skb_over_panic(), i.e. an unprivileged kernel panic (DoS), reachable
locally via userns+netns IPTFS SAs and remotely against IPTFS VPN
gateways when the decrypted outer skb is linear (e.g. AF_PACKET taps,
tun/tap delivery).

Align the runt path with the normal path by requiring the declared
inner length to cover at least the IP header size. This also subsumes
the previous >= sizeof(ra_runt) check, since the minimum IP header
is always larger than the runt buffer.

This issue was found by the autokbug dynamic kernel fuzzer at
Tencent Yunding Lab.

## Which versions are affected by CVE-2026-98371?


## How do I fix CVE-2026-98371?

Apply the vendor's patch.

## Is CVE-2026-98371 being exploited?

There is no known exploitation of CVE-2026-98371 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98371 and fix it if it is affected.

What it is: CVE-2026-98371 is a denial of service 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-2026-98371 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-2026-98371/ (Markdown: https://insights.sbomify.com/CVE-2026-98371/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98371
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98371
- OSV: https://osv.dev/vulnerability/CVE-2026-98371

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98371/
Summaries are generated and may contain mistakes; the official description above is the record.