From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-cve-announce@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@kernel.org>
Subject: CVE-2026-89561: ipv6: rpl: fix NULL dereference of idev in ipv6_rpl_srh_rcv()
Date: Fri, 11 Sep 2026 21:44:10 +0200 [thread overview]
Message-ID: <2026091123-CVE-2026-89561-82ab@gregkh> (raw)
From: Greg Kroah-Hartman <gregkh@kernel.org>
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.
The Linux kernel CVE team has assigned CVE-2026-89561 to this issue.
Affected and fixed versions
===========================
Issue introduced in 5.7 with commit 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3 and fixed in 6.18.50 with commit 63f50e9f90d0287ad66a0955ebfc2d3a9c044a1c
Issue introduced in 5.7 with commit 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3 and fixed in 7.2.4 with commit eab3a917cdcb182542a3aac6a0d2d30659ca9821
Issue introduced in 5.7 with commit 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3 and fixed in 7.3-rc1 with commit f826df95332c07380206dbd54178b6eefb311aba
Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.
Unaffected versions might change over time as fixes are backported to
older supported kernel versions. The official CVE entry at
https://cve.org/CVERecord/?id=CVE-2026-89561
will be updated if fixes are backported, please check that for the most
up to date information about this issue.
Affected files
==============
The file(s) affected by this issue are:
net/ipv6/exthdrs.c
Mitigation
==========
The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes. Individual
changes are never tested alone, but rather are part of a larger kernel
release. Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all. If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
https://git.kernel.org/stable/c/63f50e9f90d0287ad66a0955ebfc2d3a9c044a1c
https://git.kernel.org/stable/c/eab3a917cdcb182542a3aac6a0d2d30659ca9821
https://git.kernel.org/stable/c/f826df95332c07380206dbd54178b6eefb311aba
reply other threads:[~2026-09-11 19:56 UTC|newest]
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