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GHSA-4329-5QMC-M43G

Vulnerability from github – Published: 2026-09-17 18:31 – Updated: 2026-09-18 18:31

Details

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

ip6mr: do not clone dst in ip6mr_cache_report()

IPv6 input attaches a non-refcounted (NOREF) dst to skbs under RCU. When an ingress multicast packet misses MFC lookup, ip6mr_cache_unresolved() places the skb onto the unresolved queue, escaping the receive-side RCU grace period.

If the underlying route is deleted and freed, and the MFC queue is later resolved with a wrong parent interface, ip6_mr_forward() invokes ip6mr_cache_report(..., MRT6MSG_WRONGMIF), which executes dst_clone(skb_dst(pkt)) on the freed dst entry, triggering a slab use-after-free.

Report packets queued to mroute6_sk (a raw socket) and netlink notifications do not require an attached dst entry.

Fix this by: 1. Removing dst_clone() in ip6mr_cache_report() and ensuring report skbs do not hold a dst. 2. Dropping skb_dst before queuing unresolved skbs in ip6mr_cache_unresolved(), matching the fact that multicast forwarding resolves outgoing routes anew via ip6_route_output().

Severity

7.8 (High)


                  
                    CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

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{
  "affected": [],
  "aliases": [
    "CVE-2026-90111"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-17T17:17:03Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nip6mr: do not clone dst in ip6mr_cache_report()\n\nIPv6 input attaches a non-refcounted (NOREF) dst to skbs under RCU.\nWhen an ingress multicast packet misses MFC lookup,\nip6mr_cache_unresolved() places the skb onto the unresolved queue,\nescaping the receive-side RCU grace period.\n\nIf the underlying route is deleted and freed, and the MFC queue is later\nresolved with a wrong parent interface, ip6_mr_forward() invokes\nip6mr_cache_report(..., MRT6MSG_WRONGMIF), which executes\ndst_clone(skb_dst(pkt)) on the freed dst entry, triggering a slab\nuse-after-free.\n\nReport packets queued to mroute6_sk (a raw socket) and netlink\nnotifications do not require an attached dst entry.\n\nFix this by:\n1. Removing dst_clone() in ip6mr_cache_report() and ensuring report skbs\n   do not hold a dst.\n2. Dropping skb_dst before queuing unresolved skbs in\n   ip6mr_cache_unresolved(), matching the fact that multicast\n   forwarding resolves outgoing routes anew via ip6_route_output().",
  "id": "GHSA-4329-5qmc-m43g",
  "modified": "2026-09-18T18:31:27Z",
  "published": "2026-09-17T18:31:51Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-90111"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/235b42b5860189eb8c27c36435ad932cae65a734"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4a674afaae4136c71943aa3e35d433676fd40e8f"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-90111 (GCVE-0-2026-90111)

Vulnerability from cvelistv5 – Published: 2026-09-17 16:06 – Updated: 2026-09-18 17:53

Title

ip6mr: do not clone dst in ip6mr_cache_report()

Summary

In the Linux kernel, the following vulnerability has been resolved: ip6mr: do not clone dst in ip6mr_cache_report() IPv6 input attaches a non-refcounted (NOREF) dst to skbs under RCU. When an ingress multicast packet misses MFC lookup, ip6mr_cache_unresolved() places the skb onto the unresolved queue, escaping the receive-side RCU grace period. If the underlying route is deleted and freed, and the MFC queue is later resolved with a wrong parent interface, ip6_mr_forward() invokes ip6mr_cache_report(..., MRT6MSG_WRONGMIF), which executes dst_clone(skb_dst(pkt)) on the freed dst entry, triggering a slab use-after-free. Report packets queued to mroute6_sk (a raw socket) and netlink notifications do not require an attached dst entry. Fix this by: 1. Removing dst_clone() in ip6mr_cache_report() and ensuring report skbs do not hold a dst. 2. Dropping skb_dst before queuing unresolved skbs in ip6mr_cache_unresolved(), matching the fact that multicast forwarding resolves outgoing routes anew via ip6_route_output().

Severity

7.8 (High)


                        
                          CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Assigner

Linux mitre root

References

2 references

URL	Tags
https://git.kernel.org/stable/c/4a674afaae4136c71…
https://git.kernel.org/stable/c/235b42b5860189eb8…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 67f415dd29063a5906c560051c00e42dcf01a4dd , < 4a674afaae4136c71943aa3e35d433676fd40e8f (git) Affected: 67f415dd29063a5906c560051c00e42dcf01a4dd , < 235b42b5860189eb8c27c36435ad932cae65a734 (git)
Linux	Linux	Affected: 5.3 Unaffected: 0 , < 5.3 (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/ip6mr.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "4a674afaae4136c71943aa3e35d433676fd40e8f",
              "status": "affected",
              "version": "67f415dd29063a5906c560051c00e42dcf01a4dd",
              "versionType": "git"
            },
            {
              "lessThan": "235b42b5860189eb8c27c36435ad932cae65a734",
              "status": "affected",
              "version": "67f415dd29063a5906c560051c00e42dcf01a4dd",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/ipv6/ip6mr.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.3"
            },
            {
              "lessThan": "5.3",
              "status": "unaffected",
              "version": "0",
              "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": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.6",
                  "versionStartIncluding": "5.3",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3-rc1",
                  "versionStartIncluding": "5.3",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nip6mr: do not clone dst in ip6mr_cache_report()\n\nIPv6 input attaches a non-refcounted (NOREF) dst to skbs under RCU.\nWhen an ingress multicast packet misses MFC lookup,\nip6mr_cache_unresolved() places the skb onto the unresolved queue,\nescaping the receive-side RCU grace period.\n\nIf the underlying route is deleted and freed, and the MFC queue is later\nresolved with a wrong parent interface, ip6_mr_forward() invokes\nip6mr_cache_report(..., MRT6MSG_WRONGMIF), which executes\ndst_clone(skb_dst(pkt)) on the freed dst entry, triggering a slab\nuse-after-free.\n\nReport packets queued to mroute6_sk (a raw socket) and netlink\nnotifications do not require an attached dst entry.\n\nFix this by:\n1. Removing dst_clone() in ip6mr_cache_report() and ensuring report skbs\n   do not hold a dst.\n2. Dropping skb_dst before queuing unresolved skbs in\n   ip6mr_cache_unresolved(), matching the fact that multicast\n   forwarding resolves outgoing routes anew via ip6_route_output()."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The UAF is dst_clone(skb_dst(pkt)) in ip6mr_cache_report(MRT6MSG_WRONGMIF) on a NOREF dst that ip6_route_input() attached and ip6mr_cache_unresolved() queued past RCU. Completing it requires deleting that fib6 route and MRT6_ADD_MFC with mf6cc_parent != the arrival vif; those are local setsockopt/netlink from the same attacker, not a field in the IPv6 multicast datagram.\nAC:L - The attacker owns every step: MRT6_INIT/ADD_MIF/ASSERT, inject a non-link-local IPv6 multicast skb so ip6_mr_input() misses the MFC and ip6mr_cache_unresolved() queues it, delete the fib6 route and wait an RCU grace period, then MRT6_ADD_MFC with the wrong parent so ip6_mr_forward() takes the WRONGMIF path.\nPR:L - inet6_create() allows SOCK_RAW/IPPROTO_ICMPV6 only with ns_capable(CAP_NET_RAW); ip6_mroute_setsockopt() then lets that mroute socket (or ns_capable(CAP_NET_ADMIN)) run MRT6_ADD_MIF, MRT6_ASSERT, and MRT6_ADD_MFC. An unprivileged user obtains both capabilities in a user+net namespace via unshare -Urn.\nUI:N - The attacker opens the raw ICMPv6 mroute socket, adds MIFs, injects the multicast skb onto a veth, deletes the fib6 route, and installs the mismatched-parent MFC entirely with their own syscalls; no other user must mount a volume or otherwise interact.\nS:U - dst_clone()/dst_hold() touch the host kernel\u0027s struct dst_entry from the IPv6 fib looked up for the queued skb; the use-after-free stays in that networking authority and does not cross a VM, IOMMU, or other boundary.\nC:H - After the fib6 route is freed, ip6mr_cache_report() still does dst_clone(skb_dst(pkt)) and dst_hold() reads __rcuref on the dangling dst_entry; that slab UAF can be reclaimed with attacker-controlled objects and used as an arbitrary kernel read.\nI:H - dst_hold() calls rcuref_get(\u0026dst-\u003e__rcuref) on the freed dst_entry, writing a reclaimable slab object that can be sprayed to forge a refcount/control-flow hijack when the WRONGMIF report clones the stale dst.\nA:H - ip6_mr_forward() invoking ip6mr_cache_report(MRT6MSG_WRONGMIF) oopses in dst_hold()/rcuref_get() on the already-freed dst_entry even without a full exploit, so the bug is a reliable kernel crash as well as a UAF."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-18T17:53:06.232Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/4a674afaae4136c71943aa3e35d433676fd40e8f"
        },
        {
          "url": "https://git.kernel.org/stable/c/235b42b5860189eb8c27c36435ad932cae65a734"
        }
      ],
      "title": "ip6mr: do not clone dst in ip6mr_cache_report()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-90111",
    "datePublished": "2026-09-17T16:06:18.779Z",
    "dateReserved": "2026-09-11T19:38:34.787Z",
    "dateUpdated": "2026-09-18T17:53:06.232Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

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.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
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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GHSA-4329-5QMC-M43G

CVE-2026-90111 (GCVE-0-2026-90111)

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