Skip to content
Heist/ feed
Back to feed
UnratedFix available

net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop When a standalone IPv6 nexthop object is created with a loopback device (e.g., "ip -6 nexthop add id 100 dev lo"), fib6_nh_init() misclassifies it as a reject route. This is because nexthop objects have no destination prefix (fc_dst=::), causing fib6_is_reject() to match any loopback nexthop. The reject path skips fib_nh_common_init(), leaving nhc_pcpu_rth_output unallocated. If an IPv4 route later references this nexthop, __mkroute_output() dereferences NULL nhc_pcpu_rth_output and panics. Simplify the check in fib6_nh_init() to only match explicit reject routes (RTF_REJECT) instead of using fib6_is_reject(). The loopback promotion heuristic in fib6_is_reject() is handled separately by ip6_route_info_create_nh(). After this change, the three cases behave as 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_p

Products
Kernel
Affected versions
Not specified
Fixed versions
5.10.253, 5.15.203, 6.1.167, 6.12.77, 6.18.17, 6.19.7, 6.6.130
CVEs
CVE-2026-23300
Confirmed fixed CVEs
Not specified
Updated in this feed
7 Nov 2026, 18:54 UTC · Revision 1

Source evidence

net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop

core-osv · Original source

Published 25 Mar 2026, 10:26 UTC

In the Linux kernel, the following vulnerability has been resolved: net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop When a standalone IPv6 nexthop object is created with a loopback device (e.g., "ip -6 nexthop add id 100 dev lo"), fib6_nh_init() misclassifies it as a reject route. This is because nexthop objects have no destination prefix (fc_dst=::), causing fib6_is_reject() to match any loopback nexthop. The reject path skips fib_nh_common_init(), leaving nhc_pcpu_rth_output unallocated. If an IPv4 route later references this nexthop, __mkroute_output() dereferences NULL nhc_pcpu_rth_output and panics. Simplify the check in fib6_nh_init() to only match explicit reject routes (RTF_REJECT) instead of using fib6_is_reject(). The loopback promotion heuristic in fib6_is_reject() is handled separately by ip6_route_info_create_nh(). After this change, the three cases behave as 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_p

osv:CVE-2026-23300

Kernel

Fixed versions: 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.77, 6.18.17, 6.19.7

Complete source record
{
  "id": "6c0cf40c9a8e9b4dd11edb914a33605864936d0133c7fb5782999095a89ec30b",
  "url": "https://osv.dev/vulnerability/CVE-2026-23300",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop When a standalone IPv6 nexthop object is created with a loopback device (e.g., \"ip -6 nexthop add id 100 dev lo\"), fib6_nh_init() misclassifies it as a reject route. This is because nexthop objects have no destination prefix (fc_dst=::), causing fib6_is_reject() to match any loopback nexthop. The reject path skips fib_nh_common_init(), leaving nhc_pcpu_rth_output unallocated. If an IPv4 route later references this nexthop, __mkroute_output() dereferences NULL nhc_pcpu_rth_output and panics. Simplify the check in fib6_nh_init() to only match explicit reject routes (RTF_REJECT) instead of using fib6_is_reject(). The loopback promotion heuristic in fib6_is_reject() is handled separately by ip6_route_info_create_nh(). After this change, the three cases behave as 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_p",
    "evidence": "osv:CVE-2026-23300",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.10.253",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.203",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.167",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.130",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.77",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.17",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.19.7",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-23300",
      "aliases": [
        "CVE-2026-23300"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "493ced1ac47c48bb86d9d4e8e87df8592be85a0e"
                },
                {
                  "fixed": "607e68c1b7c5a30c795571be1906d716e989a644"
                },
                {
                  "fixed": "c11d7c56c2076ee9cd72004f1976fe0734df2ae9"
                },
                {
                  "fixed": "b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a"
                },
                {
                  "fixed": "b299121e7453d23faddf464087dff513a495b4fc"
                },
                {
                  "fixed": "f7c9f8e3607440fe39300efbaf46cf7b5eecb23f"
                },
                {
                  "fixed": "b3b5a037d520afe3d5276e653bc0ff516bbda34c"
                },
                {
                  "fixed": "8650db85b4259d2885d2a80fbc2317ce24194133"
                },
                {
                  "fixed": "21ec92774d1536f71bdc90b0e3d052eff99cf093"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-23300.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.3.0"
                },
                {
                  "fixed": "5.10.253"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.11.0"
                },
                {
                  "fixed": "5.15.203"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.16.0"
                },
                {
                  "fixed": "6.1.167"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
                  "fixed": "6.6.130"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.77"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.17"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "6.19.7"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-23300.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:51.605891952Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-082556.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-784472.html",
        "https://git.kernel.org/stable/c/21ec92774d1536f71bdc90b0e3d052eff99cf093",
        "https://git.kernel.org/stable/c/607e68c1b7c5a30c795571be1906d716e989a644",
        "https://git.kernel.org/stable/c/8650db85b4259d2885d2a80fbc2317ce24194133",
        "https://git.kernel.org/stable/c/b299121e7453d23faddf464087dff513a495b4fc",
        "https://git.kernel.org/stable/c/b3b5a037d520afe3d5276e653bc0ff516bbda34c",
        "https://git.kernel.org/stable/c/b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a",
        "https://git.kernel.org/stable/c/c11d7c56c2076ee9cd72004f1976fe0734df2ae9",
        "https://git.kernel.org/stable/c/f7c9f8e3607440fe39300efbaf46cf7b5eecb23f",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23300.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-23300",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23300.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-23300",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 520149,
  "published_at": "2026-03-25T10:26:56.138+00:00"
}