The vulnerability (CVE-2026-46244) exists in the Linux kernel netfilter nft_inner_parse_l2l3() function when processing inner IPv6 packets. The function ipv6_find_hdr() correctly calculates the transport header offset by traversing all IPv6 extension headers, but this calculated offset is immediately overwritten with a fixed value that only accounts for the IPv6 base header length (40 bytes). This causes a desynchronization between the inner_thoff offset (incorrectly pointing to the start of extension headers) and the l4proto value (correctly identifying the transport protocol). This desync allows an attacker to forge transport headers, potentially bypassing firewall rules. The flaw affects stable Linux kernel versions from 6.2 onward. Red Hat advisories RHSA-2026:33215 and RHSA-2026:34094 provide patches for Red Hat Enterprise Linux 10.0 and 9.6 respectively, which fix this issue by removing the incorrect overwrite and preserving the correct transport header offset.

This vulnerability can lead to transport header forgery and potential firewall bypass, which compromises the integrity and security of network packet processing. The CVSS 3.1 vector indicates a network attack vector with low attack complexity, no privileges required, no user interaction, and high confidentiality and integrity impact but no availability impact. This means an unauthenticated attacker can exploit this remotely to manipulate transport headers and evade firewall protections, potentially exposing sensitive data or allowing unauthorized network access.

Red Hat has released official security updates that fix this vulnerability in Red Hat Enterprise Linux 9.6 and 10.0 Extended Update Support releases. Users should apply the kernel updates provided in advisories RHSA-2026:33215 and RHSA-2026:34094 and reboot affected systems to ensure the fix takes effect. These updates remove the incorrect overwrite of the transport header offset, preserving the correct offset and preventing desynchronization. No additional mitigation steps are required beyond applying the official patches.