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
Metrics
Affected Vendors & Products
| Vendors | Products |
|---|---|
| Linux |
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References
History
Wed, 24 Jun 2026 17:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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 | |
| Title | nexthop: fix IPv6 route referencing IPv4 nexthop | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-06-24T16:29:22.973Z
Reserved: 2026-06-09T07:44:35.378Z
Link: CVE-2026-53012
Vulnrichment
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NVD
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Redhat
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OpenCVE Enrichment
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