Vulnerability-Lookup

GHSA-8437-C9WR-2522

Vulnerability from github – Published: 2026-09-16 09:30 – Updated: 2026-09-16 09:30

Details

In the Linux kernel, the following vulnerability has been resolved:

ipv6: avoid divide by zero in rt6_multipath_rebalance

rt6_multipath_rebalance() calculates the total eligible nexthop weight in one pass and programs upper bounds in a second pass. Since RTM_NEWROUTE is RTNL-free, a concurrent ignore_routes_with_linkdown update can make the first pass return zero while the second sees an eligible nexthop, causing rt6_upper_bound_set() to divide by zero.

UBSAN: division-overflow in net/ipv6/route.c:4845:17 Oops: divide error: 0000 [#1] SMP KASAN NOPTI rt6_upper_bound_set() net/ipv6/route.c:4845 rt6_multipath_rebalance() fib6_add_rt2node() ip6_route_multipath_add() inet6_rtm_newroute()

Skip upper-bound calculation when the first pass reports a zero total. This respects the lock-free performance considerations here and solves insecure scenarios.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-89790"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-16T09:17:09Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: avoid divide by zero in rt6_multipath_rebalance\n\nrt6_multipath_rebalance() calculates the total eligible nexthop weight\nin one pass and programs upper bounds in a second pass. Since\nRTM_NEWROUTE is RTNL-free, a concurrent\nignore_routes_with_linkdown update can make the first pass return zero\nwhile the second sees an eligible nexthop, causing\nrt6_upper_bound_set() to divide by zero.\n\nUBSAN: division-overflow in net/ipv6/route.c:4845:17\nOops: divide error: 0000 [#1] SMP KASAN NOPTI\n  rt6_upper_bound_set() net/ipv6/route.c:4845\n  rt6_multipath_rebalance()\n  fib6_add_rt2node()\n  ip6_route_multipath_add()\n  inet6_rtm_newroute()\n\nSkip upper-bound calculation when the first pass reports a zero total.\nThis respects the lock-free performance considerations here and solves\ninsecure scenarios.",
  "id": "GHSA-8437-c9wr-2522",
  "modified": "2026-09-16T09:30:30Z",
  "published": "2026-09-16T09:30:30Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89790"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d2c26c2911dd1a363c488add4fb63eb5f0f28f87"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f30cf8fd9872299c0c27f9916252ba2b9f422dce"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f82b5dbb2fef65b52a62d5ffe05e0483c4385a83"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-89790 (GCVE-0-2026-89790)

Vulnerability from cvelistv5 – Published: 2026-09-16 08:48 – Updated: 2026-09-16 08:48

Title

ipv6: avoid divide by zero in rt6_multipath_rebalance

Summary

In the Linux kernel, the following vulnerability has been resolved: ipv6: avoid divide by zero in rt6_multipath_rebalance rt6_multipath_rebalance() calculates the total eligible nexthop weight in one pass and programs upper bounds in a second pass. Since RTM_NEWROUTE is RTNL-free, a concurrent ignore_routes_with_linkdown update can make the first pass return zero while the second sees an eligible nexthop, causing rt6_upper_bound_set() to divide by zero. UBSAN: division-overflow in net/ipv6/route.c:4845:17 Oops: divide error: 0000 [#1] SMP KASAN NOPTI rt6_upper_bound_set() net/ipv6/route.c:4845 rt6_multipath_rebalance() fib6_add_rt2node() ip6_route_multipath_add() inet6_rtm_newroute() Skip upper-bound calculation when the first pass reports a zero total. This respects the lock-free performance considerations here and solves insecure scenarios.

Severity

No CVSS data available.

Assigner

Linux mitre root

References

3 references

URL	Tags
https://git.kernel.org/stable/c/f30cf8fd9872299c0…
https://git.kernel.org/stable/c/f82b5dbb2fef65b52…
https://git.kernel.org/stable/c/d2c26c2911dd1a363…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: bd11ff421d36abdb585b9104fa70057bf01b3110 , < f30cf8fd9872299c0c27f9916252ba2b9f422dce (git) Affected: bd11ff421d36abdb585b9104fa70057bf01b3110 , < f82b5dbb2fef65b52a62d5ffe05e0483c4385a83 (git) Affected: bd11ff421d36abdb585b9104fa70057bf01b3110 , < d2c26c2911dd1a363c488add4fb63eb5f0f28f87 (git)
Linux	Linux	Affected: 6.16 Unaffected: 0 , < 6.16 (semver) Unaffected: 6.18.52 , ≤ 6.18.* (semver) Unaffected: 7.2.6 , ≤ 7.2.* (semver) Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv6/route.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
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              "status": "affected",
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              "versionType": "git"
            },
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              "versionType": "git"
            },
            {
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            }
          ]
        },
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          "versions": [
            {
              "status": "affected",
              "version": "6.16"
            },
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.52",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
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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\nipv6: avoid divide by zero in rt6_multipath_rebalance\n\nrt6_multipath_rebalance() calculates the total eligible nexthop weight\nin one pass and programs upper bounds in a second pass. Since\nRTM_NEWROUTE is RTNL-free, a concurrent\nignore_routes_with_linkdown update can make the first pass return zero\nwhile the second sees an eligible nexthop, causing\nrt6_upper_bound_set() to divide by zero.\n\nUBSAN: division-overflow in net/ipv6/route.c:4845:17\nOops: divide error: 0000 [#1] SMP KASAN NOPTI\n  rt6_upper_bound_set() net/ipv6/route.c:4845\n  rt6_multipath_rebalance()\n  fib6_add_rt2node()\n  ip6_route_multipath_add()\n  inet6_rtm_newroute()\n\nSkip upper-bound calculation when the first pass reports a zero total.\nThis respects the lock-free performance considerations here and solves\ninsecure scenarios."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-16T08:48:26.343Z",
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        {
          "url": "https://git.kernel.org/stable/c/d2c26c2911dd1a363c488add4fb63eb5f0f28f87"
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      "title": "ipv6: avoid divide by zero in rt6_multipath_rebalance",
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    "datePublished": "2026-09-16T08:48:26.343Z",
    "dateReserved": "2026-09-11T19:38:34.766Z",
    "dateUpdated": "2026-09-16T08:48:26.343Z",
    "state": "PUBLISHED"
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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

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The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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