---
id: "CVE-2026-98573"
kind: "vulnerability"
aliases: ["CVE-2026-98573"]
title: "Linux kernel: IPv6 extension header parsing can underflow a copy length"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["ipv6", "linux-kernel", "networking", "runtime", "self-hosted"]
not_affected_if: ["patched-kernel"]
published_at: "2026-10-18T16:17:09+00:00"
first_seen_at: "2026-10-23T21:57:15+00:00"
updated_at: "2026-10-25T05:23:10+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98573", "first_seen_at": "2026-10-23T21:57:15+00:00"}]
---

# Linux kernel: IPv6 extension header parsing can underflow a copy length

In skb_checksum_setup_ipv6() the kernel computes a negative pull length when parsing IPv6 extension headers on a packet whose linear area is already large. The negative value becomes a very large copy, which can corrupt memory or crash the kernel.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- `uname -r` and compare against the fixed kernel builds listed in the NVD record (unknown from the sources)
- Check whether the running kernel includes the commit that passes the requested length as the pull bound in skb_checksum_setup_ipv6() (unknown from the sources)

## Fix

- Update the Linux kernel to a release that includes the upstream fix for skb_checksum_setup_ipv6() (exact version unknown from the sources)
- Reboot into the patched kernel and confirm with `uname -r`

## Timeline

- 2026-10-23T21:57:15+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98573

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

net: skbuff: fix pull-bound underflow in skb_checksum_setup_ipv6()

skb_maybe_pull_tail() subtracts skb_headlen(skb) from the unsigned max
argument and passes the result to __pskb_pull_tail() as a signed int.  The
function does not ensure that max is at least skb_headlen(skb).

This can happen while parsing IPv6 extension headers when an skb already
has a linear area larger than MAX_IPV6_HDR_LEN.  Once the parser needs data
beyond the linear area, max - skb_headlen(skb) wraps and is converted to a
negative delta.  __pskb_pull_tail() then passes that negative length to
skb_copy_bits(), where it can become a very large copy length.

Pass the requested length itself as the pull bound at the three
extension-header call sites, so the delta can no longer go negative.

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