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Linux kernel: IPv6 Router Discovery vulnerability
CVE-2026-23124
Summary
A vulnerability was found in the Linux kernel's IPv6 Router Discovery feature. This could allow an attacker to potentially manipulate the MTU (Maximum Transmission Unit) value, which could disrupt network communication. To fix this, the developers added additional safety checks to prevent this issue. The good news is that this vulnerability has already been resolved in the kernel.
Original title
In the Linux kernel, the following vulnerability has been resolved:
ipv6: annotate data-race in ndisc_router_discovery()
syzbot found that ndisc_router_discovery() could read and write
in6_dev->r...
Original description
In the Linux kernel, the following vulnerability has been resolved:
ipv6: annotate data-race in ndisc_router_discovery()
syzbot found that ndisc_router_discovery() could read and write
in6_dev->ra_mtu without holding a lock [1]
This looks fine, IFLA_INET6_RA_MTU is best effort.
Add READ_ONCE()/WRITE_ONCE() to document the race.
Note that we might also reject illegal MTU values
(mtu < IPV6_MIN_MTU || mtu > skb->dev->mtu) in a future patch.
[1]
BUG: KCSAN: data-race in ndisc_router_discovery / ndisc_router_discovery
read to 0xffff888119809c20 of 4 bytes by task 25817 on cpu 1:
ndisc_router_discovery+0x151d/0x1c90 net/ipv6/ndisc.c:1558
ndisc_rcv+0x2ad/0x3d0 net/ipv6/ndisc.c:1841
icmpv6_rcv+0xe5a/0x12f0 net/ipv6/icmp.c:989
ip6_protocol_deliver_rcu+0xb2a/0x10d0 net/ipv6/ip6_input.c:438
ip6_input_finish+0xf0/0x1d0 net/ipv6/ip6_input.c:489
NF_HOOK include/linux/netfilter.h:318 [inline]
ip6_input+0x5e/0x140 net/ipv6/ip6_input.c:500
ip6_mc_input+0x27c/0x470 net/ipv6/ip6_input.c:590
dst_input include/net/dst.h:474 [inline]
ip6_rcv_finish+0x336/0x340 net/ipv6/ip6_input.c:79
...
write to 0xffff888119809c20 of 4 bytes by task 25816 on cpu 0:
ndisc_router_discovery+0x155a/0x1c90 net/ipv6/ndisc.c:1559
ndisc_rcv+0x2ad/0x3d0 net/ipv6/ndisc.c:1841
icmpv6_rcv+0xe5a/0x12f0 net/ipv6/icmp.c:989
ip6_protocol_deliver_rcu+0xb2a/0x10d0 net/ipv6/ip6_input.c:438
ip6_input_finish+0xf0/0x1d0 net/ipv6/ip6_input.c:489
NF_HOOK include/linux/netfilter.h:318 [inline]
ip6_input+0x5e/0x140 net/ipv6/ip6_input.c:500
ip6_mc_input+0x27c/0x470 net/ipv6/ip6_input.c:590
dst_input include/net/dst.h:474 [inline]
ip6_rcv_finish+0x336/0x340 net/ipv6/ip6_input.c:79
...
value changed: 0x00000000 -> 0xe5400659
ipv6: annotate data-race in ndisc_router_discovery()
syzbot found that ndisc_router_discovery() could read and write
in6_dev->ra_mtu without holding a lock [1]
This looks fine, IFLA_INET6_RA_MTU is best effort.
Add READ_ONCE()/WRITE_ONCE() to document the race.
Note that we might also reject illegal MTU values
(mtu < IPV6_MIN_MTU || mtu > skb->dev->mtu) in a future patch.
[1]
BUG: KCSAN: data-race in ndisc_router_discovery / ndisc_router_discovery
read to 0xffff888119809c20 of 4 bytes by task 25817 on cpu 1:
ndisc_router_discovery+0x151d/0x1c90 net/ipv6/ndisc.c:1558
ndisc_rcv+0x2ad/0x3d0 net/ipv6/ndisc.c:1841
icmpv6_rcv+0xe5a/0x12f0 net/ipv6/icmp.c:989
ip6_protocol_deliver_rcu+0xb2a/0x10d0 net/ipv6/ip6_input.c:438
ip6_input_finish+0xf0/0x1d0 net/ipv6/ip6_input.c:489
NF_HOOK include/linux/netfilter.h:318 [inline]
ip6_input+0x5e/0x140 net/ipv6/ip6_input.c:500
ip6_mc_input+0x27c/0x470 net/ipv6/ip6_input.c:590
dst_input include/net/dst.h:474 [inline]
ip6_rcv_finish+0x336/0x340 net/ipv6/ip6_input.c:79
...
write to 0xffff888119809c20 of 4 bytes by task 25816 on cpu 0:
ndisc_router_discovery+0x155a/0x1c90 net/ipv6/ndisc.c:1559
ndisc_rcv+0x2ad/0x3d0 net/ipv6/ndisc.c:1841
icmpv6_rcv+0xe5a/0x12f0 net/ipv6/icmp.c:989
ip6_protocol_deliver_rcu+0xb2a/0x10d0 net/ipv6/ip6_input.c:438
ip6_input_finish+0xf0/0x1d0 net/ipv6/ip6_input.c:489
NF_HOOK include/linux/netfilter.h:318 [inline]
ip6_input+0x5e/0x140 net/ipv6/ip6_input.c:500
ip6_mc_input+0x27c/0x470 net/ipv6/ip6_input.c:590
dst_input include/net/dst.h:474 [inline]
ip6_rcv_finish+0x336/0x340 net/ipv6/ip6_input.c:79
...
value changed: 0x00000000 -> 0xe5400659
- https://git.kernel.org/stable/c/2619499169fb1c2ac4974b0f2d87767fb543582b
- https://git.kernel.org/stable/c/2a2b9d25f801afecf2f83cacce98afa8fd73e3c9
- https://git.kernel.org/stable/c/4630897eb1a039b5d7b737b8dc9521d9d4b568b5
- https://git.kernel.org/stable/c/9a063f96d87efc3a6cc667f8de096a3d38d74bb5
- https://git.kernel.org/stable/c/e3c1040252e598f7b4e33a42dc7c38519bc22428
- https://git.kernel.org/stable/c/fad8f4ff7928f4d52a062ffdcffa484989c79c47
Published: 14 Feb 2026 · Updated: 10 Mar 2026 · First seen: 6 Mar 2026