# CVE-2026-89555

## Summary

- **CVE ID:** CVE-2026-89555
- **Severity:** CRITICAL
- **CVSS Score:** 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 14, 2026

## 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_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.

## Affected Products

- Linux — Linux (9f427a0e474a67b454420c131709600d44850486)
- Linux — Linux (ad864d9fce0ec56cc8f6afe5c6a0e6d7f484b9eb)
- Linux — Linux (4.9.8)
- Linux — Linux (4.10)
- Linux — Linux (0)
- Linux — Linux (6.12.109)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)
- Linux — Linux (5.10.270)
- Linux — Linux (5.15.221)
- Linux — Linux (6.1.188)
- Linux — Linux (6.6.157)

## References

- [CNA](https://git.kernel.org/stable/c/fed638a248116b8a249bd4202d28e5934bdc65ad)
- [CNA](https://git.kernel.org/stable/c/d82b90a38c2ca8a0694428eab0e9551c23f2447d)
- [CNA](https://git.kernel.org/stable/c/49d38c1b4390412f8950d33dfaee0ccbd17beb81)
- [CNA](https://git.kernel.org/stable/c/29e63b8d9fc150cc191b1c6eb7e16e1247e1b650)
- [CNA](https://git.kernel.org/stable/c/aa4fe0b450a461aa1162fe8375f5d28f4c957df8)
- [CNA](https://git.kernel.org/stable/c/b1c0783b2facc398437ad8f8b86c636d7a78f8db)
- [CNA](https://git.kernel.org/stable/c/bfaaff99238326166694354a63a76c02563f98b1)
- [CNA](https://git.kernel.org/stable/c/d9640239827d6d0cb84263b590f7a4f1596c17eb)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.68%
- **EPSS Percentile:** 50.9

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._