CVE-2026-98598 (GCVE-0-2026-98598)

Vulnerability from cvelistv5 – Published: 2026-10-18 15:19 – Updated: 2026-10-19 09:22
VLAI
Title
ipv6: Prevent rt6_insert_exception() for dying fib6_info.
Summary
In the Linux kernel, the following vulnerability has been resolved: ipv6: Prevent rt6_insert_exception() for dying fib6_info. Before the cited commit, fib6_nh_flush_exceptions() always set from->exception_bucket_flushed = 1 under rt6_exception_lock to prevent rt6_insert_exception() from inserting a new exception for a dying fib6_info. The flag was replaced with the FIB6_EXCEPTION_BUCKET_FLUSHED bit stored in nh->rt6i_exception_bucket. The problem is that now the bit is only set when the bucket is not NULL and fib6_nh_flush_exceptions() is called from fib6_nh_release() after fib6_ref has already reached zero. If rt6_insert_exception() is called while the target fib6_info is being removed via fib6_purge_rt(), a new exception could be created successfully because rt6_flush_exceptions() no longer sets the bit. This creates a reference cycle between the fib6_info and the exception route, leaking the fib6_info, its nexthop device, and all per-CPU routes in fib6_nh->rt6i_pcpu, which stalls netdev unregistration. [ 34.680602] unregister_netdevice: waiting for gre6 to become free. Usage count = 68 [ 44.920675] unregister_netdevice: waiting for gre6 to become free. Usage count = 68 [ 55.176582] unregister_netdevice: waiting for gre6 to become free. Usage count = 68 Let's call fib6_drop_pcpu_from() before rt6_flush_exceptions(), to set fib6_destroying before rt6_exception_lock, and check f6i->fib6_destroying in rt6_insert_exception(). Note that FIB6_EXCEPTION_BUCKET_FLUSHED logic is dead and we can clean it up in net-next.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6820 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: cc5c073a693fa6ed7a207b0436114f68cce72434 , < 649ffc76ed5483b2caf35ed90d3787538efc4e53 (git)
Affected: cc5c073a693fa6ed7a207b0436114f68cce72434 , < e03e77071e75ce726d877f0a4349a28b6e1f487a (git)
Affected: cc5c073a693fa6ed7a207b0436114f68cce72434 , < 0346ec2f080b40d95ed05b853bb9226289e75212 (git)
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Linux Linux Affected: 5.3
Unaffected: 0 , < 5.3 (semver)
Unaffected: 6.18.55 , ≤ 6.18.* (semver)
Unaffected: 7.2.9 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
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{
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv6/ip6_fib.c",
            "net/ipv6/route.c"
          ],
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          "vendor": "Linux",
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              "versionType": "semver"
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              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: Prevent rt6_insert_exception() for dying fib6_info.\n\nBefore the cited commit, fib6_nh_flush_exceptions() always set\nfrom-\u003eexception_bucket_flushed = 1 under rt6_exception_lock to\nprevent rt6_insert_exception() from inserting a new exception\nfor a dying fib6_info.\n\nThe flag was replaced with the FIB6_EXCEPTION_BUCKET_FLUSHED\nbit stored in nh-\u003ert6i_exception_bucket.\n\nThe problem is that now the bit is only set when the bucket\nis not NULL and fib6_nh_flush_exceptions() is called from\nfib6_nh_release() after fib6_ref has already reached zero.\n\nIf rt6_insert_exception() is called while the target fib6_info\nis being removed via fib6_purge_rt(), a new exception could be\ncreated successfully because rt6_flush_exceptions() no longer\nsets the bit.\n\nThis creates a reference cycle between the fib6_info and the\nexception route, leaking the fib6_info, its nexthop device,\nand all per-CPU routes in fib6_nh-\u003ert6i_pcpu, which stalls netdev\nunregistration.\n\n[   34.680602] unregister_netdevice: waiting for gre6 to become free. Usage count = 68\n[   44.920675] unregister_netdevice: waiting for gre6 to become free. Usage count = 68\n[   55.176582] unregister_netdevice: waiting for gre6 to become free. Usage count = 68\n\nLet\u0027s call fib6_drop_pcpu_from() before rt6_flush_exceptions(),\nto set fib6_destroying before rt6_exception_lock, and check\nf6i-\u003efib6_destroying in rt6_insert_exception().\n\nNote that FIB6_EXCEPTION_BUCKET_FLUSHED logic is dead and\nwe can clean it up in net-next."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:22:24.055Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/e03e77071e75ce726d877f0a4349a28b6e1f487a"
        },
        {
          "url": "https://git.kernel.org/stable/c/0346ec2f080b40d95ed05b853bb9226289e75212"
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98598",
    "datePublished": "2026-10-18T15:19:11.126Z",
    "dateReserved": "2026-09-25T10:25:14.359Z",
    "dateUpdated": "2026-10-19T09:22:24.055Z",
    "state": "PUBLISHED"
  },
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  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
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      "date": "2026-11-02",
      "epss": "0.00198",
      "percentile": "0.0957"
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      "cve": "CVE-2026-98598",
      "id": "msrc_CVE-2026-98598",
      "initial_release_date": "2026-10-20T01:08:45.000Z",
      "product_status:known_affected": "2",
      "product_status:under_investigation": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "ipv6: Prevent rt6_insert_exception() for dying fib6_info.",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-98598.json",
      "version": "4"
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        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: Prevent rt6_insert_exception() for dying fib6_info.\n\nBefore the cited commit, fib6_nh_flush_exceptions() always set\nfrom-\u003eexception_bucket_flushed = 1 under rt6_exception_lock to\nprevent rt6_insert_exception() from inserting a new exception\nfor a dying fib6_info.\n\nThe flag was replaced with the FIB6_EXCEPTION_BUCKET_FLUSHED\nbit stored in nh-\u003ert6i_exception_bucket.\n\nThe problem is that now the bit is only set when the bucket\nis not NULL and fib6_nh_flush_exceptions() is called from\nfib6_nh_release() after fib6_ref has already reached zero.\n\nIf rt6_insert_exception() is called while the target fib6_info\nis being removed via fib6_purge_rt(), a new exception could be\ncreated successfully because rt6_flush_exceptions() no longer\nsets the bit.\n\nThis creates a reference cycle between the fib6_info and the\nexception route, leaking the fib6_info, its nexthop device,\nand all per-CPU routes in fib6_nh-\u003ert6i_pcpu, which stalls netdev\nunregistration.\n\n[   34.680602] unregister_netdevice: waiting for gre6 to become free. Usage count = 68\n[   44.920675] unregister_netdevice: waiting for gre6 to become free. Usage count = 68\n[   55.176582] unregister_netdevice: waiting for gre6 to become free. Usage count = 68\n\nLet\u0027s call fib6_drop_pcpu_from() before rt6_flush_exceptions(),\nto set fib6_destroying before rt6_exception_lock, and check\nf6i-\u003efib6_destroying in rt6_insert_exception().\n\nNote that FIB6_EXCEPTION_BUCKET_FLUSHED logic is dead and\nwe can clean it up in net-next."
          }
        ],
        "id": "CVE-2026-98598",
        "lastModified": "2026-10-19T10:19:21.240",
        "metrics": {},
        "published": "2026-10-18T16:17:12.500",
        "references": [
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        "vulnStatus": "Received"
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      "cve": "CVE-2026-98598",
      "id": "CVE-2026-98598",
      "initial_release_date": "2026-10-18T00:00:00+00:00",
      "product_status:known_affected": "202",
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      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ipv6: Prevent rt6_insert_exception() for dying fib6_info",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-98598.json",
      "version": "3"
    }
  }
}



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