Bug 2464420 (CVE-2026-43057)

Summary: CVE-2026-43057 kernel: net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's networking subsystem. Incorrect handling of tunneled IPv6 traffic, specifically when processing packets with IPv6 extension headers or without an inner IP protocol, can cause the system to improperly revert to a software processing path. This issue may lead to a denial of service due to degraded network performance or dropped packets.
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Description OSIDB Bzimport 2026-05-01 15:05:52 UTC 
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.
Comment 1 Keith Grant 2026-05-01 19:06:36 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050108-CVE-2026-43057-4807@gregkh/T