CVE-2026-89555

/// Technical description

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

mpls: reload header after pskb_may_pull()

mpls_select_multipath() calls mpls_multipath_hash() to choose a nexthop

when an MPLS route has multiple nexthops. While walking the MPLS label

stack, the hash routine caches hdr for the current label. After finding

the bottom-of-stack label, it calls pskb_may_pull() before reading the

inner IP header.

If an skb is constructed with the inner IP header in nonlinear data and

insufficient tailroom in the linear head, pskb_may_pull() calls

pskb_expand_head() to replace the skb head and free the old one. This

leaves hdr pointing to freed memory. The IPv6 path can invalidate hdr

again when it performs a second pull for the larger header.

The issue was found through static analysis. A reproducer sending a legal

Geneve packet through a bareudp/MPLS multipath setup triggered the same

KASAN report in 2 of 2 unpatched runs:

BUG: KASAN: slab-use-after-free in mpls_select_multipa

/// 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