# CVE-2026-89561

## Summary

- **CVE ID:** CVE-2026-89561
- **Severity:** HIGH
- **CVSS Score:** 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 13, 2026

## Description

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

ipv6: rpl: fix NULL dereference of idev in ipv6_rpl_srh_rcv()

ipv6_rpl_srh_rcv() dereferences idev from __in6_dev_get() without a NULL
check when reading idev->cnf.rpl_seg_enabled.

When the device's MTU drops below IPV6_MIN_MTU, addrconf_ifdown() clears
dev->ip6_ptr through RCU_INIT_POINTER(). A packet that passed the idev
check in ip6_rcv_core() can then reach ipv6_rpl_srh_rcv() with
dev->ip6_ptr already NULL.

Reproduced by flooding the receiving interface with ping6 traffic while
flapping its MTU between 1500 and 1200:

 BUG: KASAN: null-ptr-deref in ipv6_rpl_srh_rcv+0xb3/0x1070
 Read of size 4 at addr 00000000000006b4 by task ping6/394

 CPU: 2 UID: 0 PID: 394 Comm: ping6 Not tainted 7.2.0-rc7-micro-vm-dev-00095-g24ef02f934ee #240 PREEMPT(full)
 Call Trace:
  <IRQ>
  kasan_report+0xc6/0x100
  ipv6_rpl_srh_rcv+0xb3/0x1070
  ip6_protocol_deliver_rcu+0x759/0x9a0
  ip6_input_finish+0xa8/0x1b0
  ip6_input+0xe1/0x490
  ipv6_rcv+0x33d/0x460
  __netif_receive_skb_one_core+0xd6/0x130
  process_backlog+0x2cc/0xa00
  __napi_poll.constprop.0+0x56/0x270
  net_rx_action+0x327/0x730
  handle_softirqs+0x11e/0x630
  do_softirq+0xb3/0xf0
  </IRQ>

Both ipv6_rpl_srh_rcv() and ipv6_srh_rcv() are called only from
ipv6_rthdr_rcv(), which already has an idev lookup.

Fix the NULL dereference on the RPL path by checking idev in
ipv6_rthdr_rcv(), before it calls either function. The callees take idev as
an argument and no longer call __in6_dev_get(), so the packet is now
dropped in one place, with SKB_DROP_REASON_IPV6DISABLED on both paths.

## Affected Products

- Linux — Linux (8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3)
- Linux — Linux (5.7)
- Linux — Linux (0)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)

## References

- [CNA](https://git.kernel.org/stable/c/63f50e9f90d0287ad66a0955ebfc2d3a9c044a1c)
- [CNA](https://git.kernel.org/stable/c/eab3a917cdcb182542a3aac6a0d2d30659ca9821)
- [CNA](https://git.kernel.org/stable/c/f826df95332c07380206dbd54178b6eefb311aba)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.43%
- **EPSS Percentile:** 36.8

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