CVE-2026-23124 ipv6: annotate data-race in ndisc_router_discovery()

Medium 5.5 Published 14 Feb 2026 Updated 19 Oct 2026

A data race in the Linux kernel IPv6 neighbor discovery allows concurrent access to MTU settings, potentially causing inconsistent state.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2026-23124?

CVE-2026-23124 is a medium-severity vulnerability in Linux kernel, published on 14 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official 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

Weakness: CWE-362

Which versions are affected by CVE-2026-23124?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-23124?

Apply the vendor's patch.

Is CVE-2026-23124 being exploited?

There is no known exploitation of CVE-2026-23124 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as AZL-77706, BELL-CVE-2026-23124, DEBIAN-CVE-2026-23124, GHSA-528j-v6ch-qq32, ROOT-OS-UBUNTU-2204-CVE-2026-23124, ROOT-OS-UBUNTU-2404-CVE-2026-23124 and 1 more.