CVE-2026-53012
Received Received - Intake
Kernel Panic in Linux IPv6 Nexthop Handling

Publication date: 2026-06-24

Last updated on: 2026-06-24

Assigner: kernel.org

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
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Meta Information
Published
2026-06-24
Last Modified
2026-06-24
Generated
2026-06-25
AI Q&A
2026-06-24
EPSS Evaluated
N/A
NVD
CVE-2026-53012
EUVD
EUVD-2026-38880
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *
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Exploitability
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CWE ID Description
CWE-UNKNOWN
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Executive Summary

This vulnerability exists in the Linux kernel's handling of IPv6 and IPv4 nexthops. When an IPv6 nexthop is replaced with an IPv4 nexthop, a flag called has_v4, which indicates the presence of IPv4 members in a group, is not updated correctly. This happens because the update function is only called when changing from IPv4 to IPv6, but not the other way around.

As a result, the system mistakenly believes there are no IPv4 members in the group (has_v4=false), allowing IPv6 routes to be attached to groups that actually contain only IPv4 members. When the system later tries to look up these routes, it calls a function that returns NULL for the IPv4 member, causing a NULL pointer dereference and leading to a kernel panic.

The fix involves updating the has_v4 flag whenever the address family changes, not just when switching from IPv4 to IPv6.

Impact Analysis

This vulnerability can cause the Linux kernel to panic due to a NULL pointer dereference when handling certain IPv6 and IPv4 route configurations. This can lead to system crashes or reboots, resulting in denial of service.

Detection Guidance

This vulnerability can be detected by reproducing the conditions that trigger the kernel panic related to IPv6 nexthop referencing IPv4 nexthop. The following commands demonstrate the issue:

  • ip -6 nexthop add id 1 blackhole
  • ip nexthop add id 100 group 1
  • ip nexthop replace id 1 blackhole
  • ip -6 route add 2001:db8::/64 nhid 100
  • ping -6 2001:db8::1

If these commands cause a kernel panic, it indicates the presence of the vulnerability.

Mitigation Strategies

The provided context does not include specific mitigation steps or patches to apply. However, since the vulnerability is fixed by updating the kernel to call nh_group_v4_update whenever the address family changes, the immediate step is to update the Linux kernel to a version that includes this fix.

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