CVE-2026-23300

Description

In the Linux kernel, the following vulnerability has been resolved:net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthopWhen a standalone IPv6 nexthop object is created with a loopback device(e.g., ip -6 nexthop add id 100 dev lo), fib6_nh_init() misclassifiesit as a reject route. This is because nexthop objects have no destinationprefix (fc_dst=::), causing fib6_is_reject() to match any loopbacknexthop. The reject path skips fib_nh_common_init(), leavingnhc_pcpu_rth_output unallocated. If an IPv4 route later references thisnexthop, __mkroute_output() dereferences null nhc_pcpu_rth_output andpanics.Simplify the check in fib6_nh_init() to only match explicit rejectroutes (RTF_REJECT) instead of using fib6_is_reject(). The loopbackpromotion heuristic in fib6_is_reject() is handled separately byip6_route_info_create_nh(). After this change, the three cases behaveas follows:1. Explicit reject route (ip -6 route add unreachable 2001:db8::/64): RTF_REJECT is set, enters reject path, skips fib_nh_common_init(). No behavior change.2. Implicit loopback reject route (ip -6 route add 2001:db8::/32 dev lo): RTF_REJECT is not set, takes normal path, fib_nh_common_init() is called. ip6_route_info_create_nh() still promotes it to reject afterward. nhc_pcpu_rth_output is allocated but unused, which is harmless.3. Standalone nexthop object (ip -6 nexthop add id 100 dev lo): RTF_REJECT is not set, takes normal path, fib_nh_common_init() is called. nhc_pcpu_rth_output is properly allocated, fixing the crash when IPv4 routes reference this nexthop.

Risk Information

Associated Vulnerability

Patch Details

References

https://nvd.nist.gov/vuln/detail/CVE-2023-1234
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-1234