CVE-2026-89562: ip6_gre: fix hardware header length for NBMA tunnels

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-11 · updated 2026-10-19

Description

In the Linux kernel, the following vulnerability has been resolved: ip6_gre: fix hardware header length for NBMA tunnels ip6gre_tnl_link_config_route() accumulates the lower device's hardware header length into dev->hard_header_len whenever header_ops is set. This is incorrect for both users of header_ops. ip6gretap and ip6erspan have a fixed Ethernet hardware header length. For an NBMA ip6gre tunnel, ip6gre_header() creates only the GRE header, the optional FOU or GUE header, and the outer IPv6 header. The lower device header is headroom needed later, not part of the tunnel device's hardware header. Keep the lower device header in needed_headroom. Set hard_header_len to the tunnel header length only for ARPHRD_IP6GRE devices with header_ops, and leave the fixed Ethernet header length unchanged for tap and erspan devices.

Affected products

Linux kernel: from 4.19.162 before 4.20; from 5.4.82 before 5.5; from 5.9.13 before 5.10; 5.10 — fixed in 4.20, 5.10, 5.5, 7.3

How to fix

Upgrade to a fixed version: Linux kernel 4.20, 5.10, 5.5, 7.3. Check the vendor advisory for mitigations.

References

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