{"id":"CVE-2026-23300","state":"PUBLISHED","title":"net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop","description":"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 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.","publishedAt":"2026-03-25T10:26:56.138Z","updatedAt":"2026-10-15T01:13:50.190Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"493ced1ac47c48bb86d9d4e8e87df8592be85a0e","status":"affected","lessThan":"607e68c1b7c5a30c795571be1906d716e989a644","versionType":"git"},{"version":"493ced1ac47c48bb86d9d4e8e87df8592be85a0e","status":"affected","lessThan":"c11d7c56c2076ee9cd72004f1976fe0734df2ae9","versionType":"git"},{"version":"493ced1ac47c48bb86d9d4e8e87df8592be85a0e","status":"affected","lessThan":"b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a","versionType":"git"},{"version":"493ced1ac47c48bb86d9d4e8e87df8592be85a0e","status":"affected","lessThan":"b299121e7453d23faddf464087dff513a495b4fc","versionType":"git"},{"version":"493ced1ac47c48bb86d9d4e8e87df8592be85a0e","status":"affected","lessThan":"f7c9f8e3607440fe39300efbaf46cf7b5eecb23f","versionType":"git"},{"version":"493ced1ac47c48bb86d9d4e8e87df8592be85a0e","status":"affected","lessThan":"b3b5a037d520afe3d5276e653bc0ff516bbda34c","versionType":"git"},{"version":"493ced1ac47c48bb86d9d4e8e87df8592be85a0e","status":"affected","lessThan":"8650db85b4259d2885d2a80fbc2317ce24194133","versionType":"git"},{"version":"493ced1ac47c48bb86d9d4e8e87df8592be85a0e","status":"affected","lessThan":"21ec92774d1536f71bdc90b0e3d052eff99cf093","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/route.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.3","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.3","versionType":"semver"},{"version":"5.10.253","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.203","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.167","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.130","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.77","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.17","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.7","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/route.c"]}],"references":["https://git.kernel.org/stable/c/607e68c1b7c5a30c795571be1906d716e989a644","https://git.kernel.org/stable/c/c11d7c56c2076ee9cd72004f1976fe0734df2ae9","https://git.kernel.org/stable/c/b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a","https://git.kernel.org/stable/c/b299121e7453d23faddf464087dff513a495b4fc","https://git.kernel.org/stable/c/f7c9f8e3607440fe39300efbaf46cf7b5eecb23f","https://git.kernel.org/stable/c/b3b5a037d520afe3d5276e653bc0ff516bbda34c","https://git.kernel.org/stable/c/8650db85b4259d2885d2a80fbc2317ce24194133","https://git.kernel.org/stable/c/21ec92774d1536f71bdc90b0e3d052eff99cf093","https://cert-portal.siemens.com/productcert/html/ssa-082556.html","https://cert-portal.siemens.com/productcert/html/ssa-019113.html","https://cert-portal.siemens.com/productcert/html/ssa-457936.html","https://cert-portal.siemens.com/productcert/html/ssa-784472.html"],"weaknesses":[],"ingestedAt":"2026-10-29T20:11:21.040Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/23xxx/CVE-2026-23300.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-23300","state":"PUBLISHED","datePublished":"2026-03-25T10:26:56.138Z","dateUpdated":"2026-10-15T01:13:50.190Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-01-13T15:37:45.993Z"},"containers":{"cna":{"title":"net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop","descriptions":[{"lang":"en","value":"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 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 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