CVE-2026-89555

Status: UPDATED  |  Advisory ID: CVE-2026-89555

Key Details

Affected Products, Subsystems & Sectors

What to Know

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_multipath

Read of size 1 at addr ffff88800ecc6e20 by task ksoftirqd/1/23

Call Trace:

mpls_select_multipath

mpls_forward

__netif_receive_skb_list_core

netif_receive_skb_list_internal

napi_complete_done

gro_cell_poll

__napi_poll

net_rx_action

Freed by task 23:

kfree

pskb_expand_head

__pskb_pull_tail

mpls_select_multipath

Reload hdr from the current skb head after each successful pull before

deriving the inner IPv4 or IPv6 header pointer. (NVD)

What to Do

Monitor Linux's web page for any future patch releases.

References