{"id":"CVE-2026-23300","title":"net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop\n\nWhen a standalone IPv6 nexthop object is created with a loopback device\n(e.g., \"ip -6 nexthop add…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < 607e68c1b7c5a30c795571be1906d716e989a644","Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < c11d7c56c2076ee9cd72004f1976fe0734df2ae9","Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a","Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < b299121e7453d23faddf464087dff513a495b4fc","Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < f7c9f8e3607440fe39300efbaf46cf7b5eecb23f","Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < b3b5a037d520afe3d5276e653bc0ff516bbda34c","Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < 8650db85b4259d2885d2a80fbc2317ce24194133","Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < 21ec92774d1536f71bdc90b0e3d052eff99cf093","Linux 5.3"],"published":"2026-03-25","updated":"2026-09-08","sourceUpdated":"2026-09-08T08:45:31.317Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-23300","references":[{"url":"https://git.kernel.org/stable/c/607e68c1b7c5a30c795571be1906d716e989a644"},{"url":"https://git.kernel.org/stable/c/c11d7c56c2076ee9cd72004f1976fe0734df2ae9"},{"url":"https://git.kernel.org/stable/c/b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a"},{"url":"https://git.kernel.org/stable/c/b299121e7453d23faddf464087dff513a495b4fc"},{"url":"https://git.kernel.org/stable/c/f7c9f8e3607440fe39300efbaf46cf7b5eecb23f"},{"url":"https://git.kernel.org/stable/c/b3b5a037d520afe3d5276e653bc0ff516bbda34c"},{"url":"https://git.kernel.org/stable/c/8650db85b4259d2885d2a80fbc2317ce24194133"},{"url":"https://git.kernel.org/stable/c/21ec92774d1536f71bdc90b0e3d052eff99cf093"}],"tags":["cve.org"],"epss":0.00129,"epssPercentile":0.02877,"ingestedAt":"2026-09-08T15:33:26.993Z","slug":"CVE-2026-23300","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop\n\nWhen a standalone IPv6 nexthop object is created with a loopback device\n(e.g., \"ip -6 nexthop add id 100 dev lo\"), fib6_nh_init() misclassifies\nit as a reject route. This is because nexthop objects have no destination\nprefix (fc_dst=::), causing fib6_is_reject() to match any loopback\nnexthop. The reject path skips fib_nh_common_init(), leaving\nnhc_pcpu_rth_output unallocated. If an IPv4 route later references this\nnexthop, __mkroute_output() dereferences NULL nhc_pcpu_rth_output and\npanics.\n\nSimplify the check in fib6_nh_init() to only match explicit reject\nroutes (RTF_REJECT) instead of using fib6_is_reject(). The loopback\npromotion heuristic in fib6_is_reject() is handled separately by\nip6_route_info_create_nh(). After this change, the three cases behave\nas follows:\n\n1. Explicit reject route (\"ip -6 route add unreachable 2001:db8::/64\"):\n   RTF_REJECT is set, enters reject path, skips fib_nh_common_init().\n   No behavior change.\n\n2. Implicit loopback reject route (\"ip -6 route add 2001:db8::/32 dev lo\"):\n   RTF_REJECT is not set, takes normal path, fib_nh_common_init() is\n   called. ip6_route_info_create_nh() still promotes it to reject\n   afterward. nhc_pcpu_rth_output is allocated but unused, which is\n   harmless.\n\n3. Standalone nexthop object (\"ip -6 nexthop add id 100 dev lo\"):\n   RTF_REJECT is not set, takes normal path, fib_nh_common_init() is\n   called. nhc_pcpu_rth_output is properly allocated, fixing the crash\n   when IPv4 routes reference this nexthop.\n\n## Affected\n\n- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < 607e68c1b7c5a30c795571be1906d716e989a644`\n- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < c11d7c56c2076ee9cd72004f1976fe0734df2ae9`\n- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a`\n- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < b299121e7453d23faddf464087dff513a495b4fc`\n- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < f7c9f8e3607440fe39300efbaf46cf7b5eecb23f`\n- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < b3b5a037d520afe3d5276e653bc0ff516bbda34c`\n- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < 8650db85b4259d2885d2a80fbc2317ce24194133`\n- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < 21ec92774d1536f71bdc90b0e3d052eff99cf093`\n- `Linux 5.3`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}