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net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels seg6_input_core() and rpl_input() call ip6_route_input() which sets a NOREF dst on the skb, then pass it to dst_cache_set_ip6() invoking dst_hold() unconditionally. On PREEMPT_RT, ksoftirqd is preemptible and a higher-priority task can release the underlying pcpu_rt between the lookup and the caching through a concurrent FIB lookup on a shared nexthop. Simplified race sequence: ksoftirqd/X higher-prio task (same CPU X) ----------- -------------------------------- seg6_input_core(,skb)/rpl_input(skb) dst_cache_get() -> miss ip6_route_input(skb) -> ip6_pol_route(,skb,flags) [RT6_LOOKUP_F_DST_NOREF in flags] -> FIB lookup resolves fib6_nh [nhid=N route] -> rt6_make_pcpu_route() [creates pcpu_rt, refcount=1] pcpu_rt->sernum = fib6_sernum [fib6_sernum=W] -> cmpxchg(fib6_nh.rt6i_pcpu, NULL, pcpu_rt) [slot was empty, store succeeds] -> skb_dst_set_noref(skb, dst) [dst is pcpu_rt, refcount still 1] rt_genid_bump_ipv6() -> bumps fib6_sernum [fib6_sernum from W to Z] ip6_route_output() -> ip6_pol_route() -> FIB lookup resolves fib6_nh [nhid=N] -> rt6_get_pcpu_route() pcpu_rt->sernum != fib6_sernum [W <> Z, stale] -> prev = xchg(rt6i_pcpu, NULL) -> dst_release(prev) [prev is pcpu_rt, refcount 1->0, dead] dst = skb_dst(skb) [dst is the dead pcpu_rt] dst_cache_set_ip6(dst) -> dst_hold() on dead dst -> WARN / use-after-free For the race to occur, ksoftirqd must be pree

Products
Kernel
Affected versions
Not specified
Fixed versions
5.15.209, 6.1.175, 6.12.86, 6.18.27, 6.6.140, 7.0.4
CVEs
CVE-2026-46099
Confirmed fixed CVEs
Not specified
Updated in this feed
3 Nov 2026, 06:28 UTC · Revision 1

Source evidence

net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels

core-osv · Original source

Published 27 May 2026, 12:59 UTC

In the Linux kernel, the following vulnerability has been resolved: net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels seg6_input_core() and rpl_input() call ip6_route_input() which sets a NOREF dst on the skb, then pass it to dst_cache_set_ip6() invoking dst_hold() unconditionally. On PREEMPT_RT, ksoftirqd is preemptible and a higher-priority task can release the underlying pcpu_rt between the lookup and the caching through a concurrent FIB lookup on a shared nexthop. Simplified race sequence: ksoftirqd/X higher-prio task (same CPU X) ----------- -------------------------------- seg6_input_core(,skb)/rpl_input(skb) dst_cache_get() -> miss ip6_route_input(skb) -> ip6_pol_route(,skb,flags) [RT6_LOOKUP_F_DST_NOREF in flags] -> FIB lookup resolves fib6_nh [nhid=N route] -> rt6_make_pcpu_route() [creates pcpu_rt, refcount=1] pcpu_rt->sernum = fib6_sernum [fib6_sernum=W] -> cmpxchg(fib6_nh.rt6i_pcpu, NULL, pcpu_rt) [slot was empty, store succeeds] -> skb_dst_set_noref(skb, dst) [dst is pcpu_rt, refcount still 1] rt_genid_bump_ipv6() -> bumps fib6_sernum [fib6_sernum from W to Z] ip6_route_output() -> ip6_pol_route() -> FIB lookup resolves fib6_nh [nhid=N] -> rt6_get_pcpu_route() pcpu_rt->sernum != fib6_sernum [W <> Z, stale] -> prev = xchg(rt6i_pcpu, NULL) -> dst_release(prev) [prev is pcpu_rt, refcount 1->0, dead] dst = skb_dst(skb) [dst is the dead pcpu_rt] dst_cache_set_ip6(dst) -> dst_hold() on dead dst -> WARN / use-after-free For the race to occur, ksoftirqd must be pree

osv:CVE-2026-46099

Kernel

Fixed versions: 5.15.209, 6.1.175, 6.6.140, 6.12.86, 6.18.27, 7.0.4

Complete source record
{
  "id": "d30b2397680e6e7c18f7176d66387c3e75c9974677ac947e5f8f38e2aa5a3bae",
  "url": "https://osv.dev/vulnerability/CVE-2026-46099",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels seg6_input_core() and rpl_input() call ip6_route_input() which sets a NOREF dst on the skb, then pass it to dst_cache_set_ip6() invoking dst_hold() unconditionally. On PREEMPT_RT, ksoftirqd is preemptible and a higher-priority task can release the underlying pcpu_rt between the lookup and the caching through a concurrent FIB lookup on a shared nexthop. Simplified race sequence: ksoftirqd/X higher-prio task (same CPU X) ----------- -------------------------------- seg6_input_core(,skb)/rpl_input(skb) dst_cache_get() -> miss ip6_route_input(skb) -> ip6_pol_route(,skb,flags) [RT6_LOOKUP_F_DST_NOREF in flags] -> FIB lookup resolves fib6_nh [nhid=N route] -> rt6_make_pcpu_route() [creates pcpu_rt, refcount=1] pcpu_rt->sernum = fib6_sernum [fib6_sernum=W] -> cmpxchg(fib6_nh.rt6i_pcpu, NULL, pcpu_rt) [slot was empty, store succeeds] -> skb_dst_set_noref(skb, dst) [dst is pcpu_rt, refcount still 1] rt_genid_bump_ipv6() -> bumps fib6_sernum [fib6_sernum from W to Z] ip6_route_output() -> ip6_pol_route() -> FIB lookup resolves fib6_nh [nhid=N] -> rt6_get_pcpu_route() pcpu_rt->sernum != fib6_sernum [W <> Z, stale] -> prev = xchg(rt6i_pcpu, NULL) -> dst_release(prev) [prev is pcpu_rt, refcount 1->0, dead] dst = skb_dst(skb) [dst is the dead pcpu_rt] dst_cache_set_ip6(dst) -> dst_hold() on dead dst -> WARN / use-after-free For the race to occur, ksoftirqd must be pree",
    "evidence": "osv:CVE-2026-46099",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.15.209",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.175",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.140",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.86",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.27",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.0.4",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-46099",
      "aliases": [
        "CVE-2026-46099"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                {
                  "fixed": "51fef5a7c4d160839199e941929456ba21ddf73c"
                },
                {
                  "fixed": "b258b849a580285a1692e782ebc902b44c884a71"
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                {
                  "fixed": "6bd17925bd6866027a6555db17905b9fc073d38d"
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                {
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                },
                {
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                {
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                },
                {
                  "fixed": "f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-46099.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "4.12.0"
                },
                {
                  "fixed": "5.15.209"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.16.0"
                },
                {
                  "fixed": "6.1.175"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
                  "fixed": "6.6.140"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.86"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.27"
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            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.0.4"
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              ]
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          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-46099.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:26.334740608Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-784472.html",
        "https://git.kernel.org/stable/c/51fef5a7c4d160839199e941929456ba21ddf73c",
        "https://git.kernel.org/stable/c/52f9db67f8f35f436366cf4980b4f0a2583d0ef0",
        "https://git.kernel.org/stable/c/6bd17925bd6866027a6555db17905b9fc073d38d",
        "https://git.kernel.org/stable/c/9dd5481f960e337b81d7dfe429529495c1c481c0",
        "https://git.kernel.org/stable/c/b258b849a580285a1692e782ebc902b44c884a71",
        "https://git.kernel.org/stable/c/b778b6d095421619c331fd2d7751143cd5387103",
        "https://git.kernel.org/stable/c/f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e",
        "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-46099.json",
        "https://access.redhat.com/errata/RHSA-2026:45114",
        "https://access.redhat.com/errata/RHSA-2026:59662",
        "https://access.redhat.com/errata/RHSA-2026:59663",
        "https://access.redhat.com/errata/RHSA-2026:62568",
        "https://access.redhat.com/errata/RHSA-2026:64767",
        "https://access.redhat.com/errata/RHSA-2026:65712",
        "https://access.redhat.com/security/cve/CVE-2026-46099",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46099.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-46099",
        "https://bugzilla.redhat.com/show_bug.cgi?id=2481972",
        "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/2026/46xxx/CVE-2026-46099.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-46099",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 493043,
  "published_at": "2026-05-27T12:59:04.628+00:00"
}