CVE-2026-46099 (GCVE-0-2026-46099)
Vulnerability from cvelistv5
Published
2026-05-27 12:59
Modified
2026-06-14 17:54
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 preemptible (PREEMPT_RT without PREEMPT_RT_NEEDS_BH_LOCK) and a concurrent task must be able to release the pcpu_rt. Shared nexthop objects provide such a path, as two routes pointing to the same nhid share the same fib6_nh and its rt6i_pcpu entry. Fix seg6_input_core() and rpl_input() by calling skb_dst_force() after ip6_route_input() to force the NOREF dst into a refcounted one before caching. The output path is not affected as ip6_route_output() already returns a refcounted dst.
Impacted products
Vendor Product Version
Linux Linux Version: af4a2209b1344939eaac11f269c261d347cbc3ee
Version: af4a2209b1344939eaac11f269c261d347cbc3ee
Version: af4a2209b1344939eaac11f269c261d347cbc3ee
Version: af4a2209b1344939eaac11f269c261d347cbc3ee
Version: af4a2209b1344939eaac11f269c261d347cbc3ee
Version: af4a2209b1344939eaac11f269c261d347cbc3ee
Version: af4a2209b1344939eaac11f269c261d347cbc3ee
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv6/rpl_iptunnel.c",
            "net/ipv6/seg6_iptunnel.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
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          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/ipv6/rpl_iptunnel.c",
            "net/ipv6/seg6_iptunnel.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "0",
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              "version": "5.15.209",
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            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.175",
              "versionType": "semver"
            },
            {
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              "status": "unaffected",
              "version": "6.6.140",
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            },
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              "status": "unaffected",
              "version": "6.12.86",
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            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.27",
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            },
            {
              "lessThanOrEqual": "7.0.*",
              "status": "unaffected",
              "version": "7.0.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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                  "vulnerable": true
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels\n\nseg6_input_core() and rpl_input() call ip6_route_input() which sets a\nNOREF dst on the skb, then pass it to dst_cache_set_ip6() invoking\ndst_hold() unconditionally.\nOn PREEMPT_RT, ksoftirqd is preemptible and a higher-priority task can\nrelease the underlying pcpu_rt between the lookup and the caching\nthrough a concurrent FIB lookup on a shared nexthop.\nSimplified race sequence:\n\n  ksoftirqd/X                       higher-prio task (same CPU X)\n  -----------                       --------------------------------\n  seg6_input_core(,skb)/rpl_input(skb)\n    dst_cache_get()\n      -\u003e miss\n    ip6_route_input(skb)\n      -\u003e ip6_pol_route(,skb,flags)\n         [RT6_LOOKUP_F_DST_NOREF in flags]\n        -\u003e FIB lookup resolves fib6_nh\n           [nhid=N route]\n        -\u003e rt6_make_pcpu_route()\n           [creates pcpu_rt, refcount=1]\n             pcpu_rt-\u003esernum = fib6_sernum\n             [fib6_sernum=W]\n           -\u003e cmpxchg(fib6_nh.rt6i_pcpu,\n                      NULL, pcpu_rt)\n              [slot was empty, store succeeds]\n      -\u003e skb_dst_set_noref(skb, dst)\n         [dst is pcpu_rt, refcount still 1]\n\n                                    rt_genid_bump_ipv6()\n                                      -\u003e bumps fib6_sernum\n                                         [fib6_sernum from W to Z]\n                                    ip6_route_output()\n                                      -\u003e ip6_pol_route()\n                                        -\u003e FIB lookup resolves fib6_nh\n                                           [nhid=N]\n                                        -\u003e rt6_get_pcpu_route()\n                                             pcpu_rt-\u003esernum != fib6_sernum\n                                             [W \u003c\u003e Z, stale]\n                                          -\u003e prev = xchg(rt6i_pcpu, NULL)\n                                          -\u003e dst_release(prev)\n                                             [prev is pcpu_rt,\n                                              refcount 1-\u003e0, dead]\n\n    dst = skb_dst(skb)\n    [dst is the dead pcpu_rt]\n    dst_cache_set_ip6(dst)\n      -\u003e dst_hold() on dead dst\n      -\u003e WARN / use-after-free\n\nFor the race to occur, ksoftirqd must be preemptible (PREEMPT_RT without\nPREEMPT_RT_NEEDS_BH_LOCK) and a concurrent task must be able to release\nthe pcpu_rt. Shared nexthop objects provide such a path, as two routes\npointing to the same nhid share the same fib6_nh and its rt6i_pcpu\nentry.\n\nFix seg6_input_core() and rpl_input() by calling skb_dst_force() after\nip6_route_input() to force the NOREF dst into a refcounted one before\ncaching.\nThe output path is not affected as ip6_route_output() already returns a\nrefcounted dst."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.1,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          }
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-06-14T17:54:21.059Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/51fef5a7c4d160839199e941929456ba21ddf73c"
        },
        {
          "url": "https://git.kernel.org/stable/c/b258b849a580285a1692e782ebc902b44c884a71"
        },
        {
          "url": "https://git.kernel.org/stable/c/6bd17925bd6866027a6555db17905b9fc073d38d"
        },
        {
          "url": "https://git.kernel.org/stable/c/52f9db67f8f35f436366cf4980b4f0a2583d0ef0"
        },
        {
          "url": "https://git.kernel.org/stable/c/b778b6d095421619c331fd2d7751143cd5387103"
        },
        {
          "url": "https://git.kernel.org/stable/c/9dd5481f960e337b81d7dfe429529495c1c481c0"
        },
        {
          "url": "https://git.kernel.org/stable/c/f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e"
        }
      ],
      "title": "net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-46099",
    "datePublished": "2026-05-27T12:59:04.628Z",
    "dateReserved": "2026-05-13T15:03:33.097Z",
    "dateUpdated": "2026-06-14T17:54:21.059Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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