CVE-2026-74743 (GCVE-0-2026-74743)

Vulnerability from cvelistv5 – Published: 2026-08-26 14:36 – Updated: 2026-08-27 05:01
VLAI
Title
macvlan: inherit needed_headroom and needed_tailroom from lowerdev
Summary
In the Linux kernel, the following vulnerability has been resolved: macvlan: inherit needed_headroom and needed_tailroom from lowerdev macvlan devices inherit hard_header_len from lowerdev during macvlan_init(), but leave needed_headroom and needed_tailroom set to 0. When the underlying lowerdev requires extra headroom or tailroom for headers/trailers (e.g. macsec, ipsec, wireguard, tunnels, or veth with rx headroom), upper layers calculating packet headroom and tailroom fail to reserve sufficient space. This can result in reallocation overhead, skb headroom underflows, or KASAN slab-use-after-free crashes when dev_hard_header() / macvlan_hard_header() prepends header data or when lower devices append tailroom. Fix this by: 1. Inheriting needed_headroom and needed_tailroom from lowerdev in macvlan_init(). 2. Propagating needed_headroom and needed_tailroom updates to attached macvlans in macvlan_device_event() when receiving NETDEV_FEAT_CHANGE events.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53 , < 8cd90e850e434577bf6774778657d26d6995e53f (git)
Affected: b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53 , < 28afc87bd8da0b3348bbbd834c8a89e83712cf5e (git)
Affected: b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53 , < 8f6a05dbac05725e0786701eb04778c5bdbe4eaa (git)
Affected: b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53 , < 96fa90b74385b7f2b0d97251dd43d5ee6ca44668 (git)
Affected: b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53 , < bc9a00fb78e32bccc39d763bfd13a450705bac5d (git)
Affected: b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53 , < cef51860becd9700217c81732ca1eb1ea6ed6fe1 (git)
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Linux Linux Affected: 2.6.23
Unaffected: 0 , < 2.6.23 (semver)
Unaffected: 6.1.184 , ≤ 6.1.* (semver)
Unaffected: 6.6.153 , ≤ 6.6.* (semver)
Unaffected: 6.12.105 , ≤ 6.12.* (semver)
Unaffected: 6.18.46 , ≤ 6.18.* (semver)
Unaffected: 7.1.10 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmacvlan: inherit needed_headroom and needed_tailroom from lowerdev\n\nmacvlan devices inherit hard_header_len from lowerdev during macvlan_init(),\nbut leave needed_headroom and needed_tailroom set to 0.\n\nWhen the underlying lowerdev requires extra headroom or tailroom for\nheaders/trailers (e.g. macsec, ipsec, wireguard, tunnels, or veth with rx\nheadroom), upper layers calculating packet headroom and tailroom fail to\nreserve sufficient space.\n\nThis can result in reallocation overhead, skb headroom underflows, or KASAN\nslab-use-after-free crashes when dev_hard_header() / macvlan_hard_header()\nprepends header data or when lower devices append tailroom.\n\nFix this by:\n1. Inheriting needed_headroom and needed_tailroom from lowerdev in macvlan_init().\n2. Propagating needed_headroom and needed_tailroom updates to attached macvlans\n   in macvlan_device_event() when receiving NETDEV_FEAT_CHANGE events."
        }
      ],
      "metrics": [
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            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The bug fires on the macvlan transmit path (ip_finish_output2/neigh_resolve_output/macvlan_hard_header) when kernel-generated replies or forwarded traffic egress a macvlan netdev; remote peers trigger this by sending TCP/UDP/ICMP to an address on a pre-configured macvlan interface.\nAC:L - Once macvlan is stacked on a lowerdev with nonzero needed_headroom (WireGuard, MACsec, IPsec, tunnels, veth RX headroom), ordinary packets reliably hit under-reserved skb headroom/tailroom during dev_hard_header() without races or uncontrollable timing.\nPR:N - A remote attacker needs no local account or capabilities; sending routable traffic to a macvlan address suffices. Administrative macvlan setup is environmental (like other netdev CVEs), not an attacker privilege requirement.\nUI:N - Exploitation requires only normal network delivery to a reachable macvlan address; no victim must open files, mount filesystems, or perform any interactive action beyond existing connectivity.\nS:U - Impact is kernel skb heap corruption, slab-use-after-free, or panic within the host network stack; it does not cross VM, IOMMU, or container security boundaries into a separate authority.\nC:H - The fix commit documents KASAN slab-use-after-free from skb headroom underflow during header prepending; this class of kernel heap corruption is exploitable for arbitrary memory disclosure beyond a bounded leak.\nI:H - Insufficient headroom causes skb_push underflows and slab UAF during pskb_expand_head/reallocation, providing kernel heap write primitives that can be leveraged for control-flow hijacking and privilege escalation.\nA:H - The failure mode includes skb_under_panic (kernel BUG/panic) and KASAN-detected slab UAF crashes, causing immediate host kernel denial of service on affected transmit paths."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-27T05:01:04.222Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/8cd90e850e434577bf6774778657d26d6995e53f"
        },
        {
          "url": "https://git.kernel.org/stable/c/28afc87bd8da0b3348bbbd834c8a89e83712cf5e"
        },
        {
          "url": "https://git.kernel.org/stable/c/8f6a05dbac05725e0786701eb04778c5bdbe4eaa"
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        },
        {
          "url": "https://git.kernel.org/stable/c/cef51860becd9700217c81732ca1eb1ea6ed6fe1"
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74743",
    "datePublished": "2026-08-26T14:36:54.175Z",
    "dateReserved": "2026-08-15T05:44:03.930Z",
    "dateUpdated": "2026-08-27T05:01:04.222Z",
    "state": "PUBLISHED"
  },
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      "date": "2026-09-26",
      "epss": "0.00701",
      "percentile": "0.51284"
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      "cve": "CVE-2026-74743",
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      "product_status:known_affected": "2",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "macvlan: inherit needed_headroom and needed_tailroom from lowerdev",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-74743.json",
      "version": "2"
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                "product": "Linux",
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                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
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                    "status": "affected",
                    "version": "2.6.23"
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        ],
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        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmacvlan: inherit needed_headroom and needed_tailroom from lowerdev\n\nmacvlan devices inherit hard_header_len from lowerdev during macvlan_init(),\nbut leave needed_headroom and needed_tailroom set to 0.\n\nWhen the underlying lowerdev requires extra headroom or tailroom for\nheaders/trailers (e.g. macsec, ipsec, wireguard, tunnels, or veth with rx\nheadroom), upper layers calculating packet headroom and tailroom fail to\nreserve sufficient space.\n\nThis can result in reallocation overhead, skb headroom underflows, or KASAN\nslab-use-after-free crashes when dev_hard_header() / macvlan_hard_header()\nprepends header data or when lower devices append tailroom.\n\nFix this by:\n1. Inheriting needed_headroom and needed_tailroom from lowerdev in macvlan_init().\n2. Propagating needed_headroom and needed_tailroom updates to attached macvlans\n   in macvlan_device_event() when receiving NETDEV_FEAT_CHANGE events."
          }
        ],
        "id": "CVE-2026-74743",
        "lastModified": "2026-08-27T06:17:24.113",
        "metrics": {
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                "attackVector": "NETWORK",
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                "baseScore": 9.8,
                "baseSeverity": "CRITICAL",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
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              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
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      "current_release_date": "2026-08-27T07:15:31+00:00",
      "cve": "CVE-2026-74743",
      "id": "CVE-2026-74743",
      "initial_release_date": "2026-08-26T00:00:00+00:00",
      "product_status:known_affected": "260",
      "product_status:under_investigation": "14",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: macvlan: inherit needed_headroom and needed_tailroom from lowerdev",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74743.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-09-23T17:01:01Z",
      "cve": "CVE-2026-74743",
      "id": "CVE-2026-74743",
      "initial_release_date": "2026-08-27T00:21:26Z",
      "product_status:first_fixed": "68",
      "product_status:known_affected": "562",
      "product_status:known_not_affected": "89",
      "product_status:recommended": "96",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-74743",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-74743.json",
      "version": "9"
    }
  }
}



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