CVE-2026-89563

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

ip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()

ip6_tnl_xmit() may need to expand headroom before it can push the

outer IPv6 and optional encap headers. It currently does that with

skb_realloc_headroom(), copies skb->sk ownership, consumes the original

skb, and then continues processing with the replacement skb kept only in

its local variable.

That is safe only if the helper cannot fail afterwards. But this helper

still has post-reallocation error exits. collect_md tunnels reject

non-NONE encap after the replacement, and ip6_tnl_encap() can also fail

later. In those cases the helper returns an error to its callers while

the caller still only has the original skb pointer.

Both ip6_tnl_start_xmit() and the IPv6 GRE paths free the caller skb on

error, so they can end up freeing an skb that ip6_tnl_xmit() already

consumed.

Use skb_cow_head() instead. It provides the required headroom and

writability without privately

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References