CVE-2026-43057: net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-01 · updated 2026-10-15

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.

Affected products

Linux kernel: from 6.1.149 before 6.1.168; from 6.6.103 before 6.6.134; from 6.12.44 before 6.12.81; from 6.16.4 before 6.17; from 6.17.1 (excl.) before 6.18.22; from 6.19 before 6.19.12 — fixed in 6.1.168, 6.12.81, 6.17, 6.18.22, 6.19.12, 6.6.134

How to fix

Upgrade to a fixed version: Linux kernel 6.1.168, 6.12.81, 6.17, 6.18.22. Check the vendor advisory for mitigations.

References

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