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CVE-2026-23300

Full vulnerability record from the local CVENow database.

Description

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.

Severity
MEDIUM
CVSS score
5.5 (v3.1)
Vulnerability status
Modified
Source identifier
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published
2026-03-25 11:16:25.623000
Last modified
2026-11-05 22:18:13.057000
View original CVE JSON 
{
  "id": "CVE-2026-23300",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2026-03-25T11:16:25.623",
  "lastModified": "2026-11-05T22:18:13.057",
  "vulnStatus": "Modified",
  "cveTags": [],
  "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."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nnet: ipv6: corrige el pánico cuando una ruta IPv4 referencia un nexthop IPv6 de loopback\n\nCuando se crea un objeto nexthop IPv6 independiente con un dispositivo de loopback (p. ej., 'ip -6 nexthop add id 100 dev lo'), fib6_nh_init() lo clasifica erróneamente como una ruta de rechazo. Esto se debe a que los objetos nexthop no tienen prefijo de destino (fc_dst=::), lo que hace que fib6_is_reject() coincida con cualquier nexthop de loopback. La ruta de rechazo omite fib_nh_common_init(), dejando nhc_pcpu_rth_output sin asignar. Si una ruta IPv4 referencia posteriormente este nexthop, __mkroute_output() desreferencia nhc_pcpu_rth_output NULL y entra en pánico.\n\nSimplificar la verificación en fib6_nh_init() para que solo coincida con rutas de rechazo explícitas (RTF_REJECT) en lugar de usar fib6_is_reject(). La heurística de promoción de loopback en fib6_is_reject() se maneja por separado por ip6_route_info_create_nh(). Después de este cambio, los tres casos se comportan de la siguiente manera:\n\n1. Ruta de rechazo explícita ('ip -6 route add unreachable 2001:db8::/64'):\n   RTF_REJECT está configurado, entra en la ruta de rechazo, omite fib_nh_common_init().\n   Sin cambio de comportamiento.\n\n2. Ruta de rechazo de loopback implícita ('ip -6 route add 2001:db8::/32 dev lo'):\n   RTF_REJECT no está configurado, toma la ruta normal, se llama a fib_nh_common_init().\n   ip6_route_info_create_nh() aún lo promueve a rechazo posteriormente. nhc_pcpu_rth_output se asigna pero no se usa, lo cual es inofensivo.\n\n3. Objeto nexthop independiente ('ip -6 nexthop add id 100 dev lo'):\n   RTF_REJECT no está configurado, toma la ruta normal, se llama a fib_nh_common_init().\n   nhc_pcpu_rth_output se asigna correctamente, corrigiendo el fallo cuando las rutas IPv4 referencian este nexthop."
    }
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