CVE-2026-23300 (GCVE-0-2026-23300)
Vulnerability from cvelistv5
Published
2026-03-25 10:26
Modified
2026-05-11 22:04
Severity ?
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_pcpu_rth_output is properly allocated, fixing the crash when IPv4 routes reference this nexthop.
References
Impacted products
Vendor Product Version
Linux Linux Version: 493ced1ac47c48bb86d9d4e8e87df8592be85a0e
Version: 493ced1ac47c48bb86d9d4e8e87df8592be85a0e
Version: 493ced1ac47c48bb86d9d4e8e87df8592be85a0e
Version: 493ced1ac47c48bb86d9d4e8e87df8592be85a0e
Version: 493ced1ac47c48bb86d9d4e8e87df8592be85a0e
Version: 493ced1ac47c48bb86d9d4e8e87df8592be85a0e
Version: 493ced1ac47c48bb86d9d4e8e87df8592be85a0e
Version: 493ced1ac47c48bb86d9d4e8e87df8592be85a0e
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{
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      "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 nexthop."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-05-11T22:04:13.060Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "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"
        }
      ],
      "title": "net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop",
      "x_generator": {
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      }
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-23300",
    "datePublished": "2026-03-25T10:26:56.138Z",
    "dateReserved": "2026-01-13T15:37:45.993Z",
    "dateUpdated": "2026-05-11T22:04:13.060Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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