GHSA-2VPJ-2C73-PM86
Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-08-17 06:33In the Linux kernel, the following vulnerability has been resolved:
flow_dissector: check device type before reading ETH_ADDRS
__skb_flow_dissect() unconditionally reads 12 bytes from eth_hdr(skb) when FLOW_DISSECTOR_KEY_ETH_ADDRS is requested. This assumes the skb has a valid Ethernet header at mac_header, which is not always the case.
The problem can be triggered by: 1. Creating a TUN device in L3 mode (IFF_TUN, hard_header_len=0) 2. Attaching a multiq qdisc with a flower filter matching on eth_src 3. Sending a packet through AF_PACKET
Since TUN in L3 mode has no link-layer header, mac_header points to the L3 data area. The flow dissector reads 12 bytes of uninitialized skb memory, which then propagates through fl_set_masked_key() and is used as a rhashtable lookup key in __fl_lookup(), as reported by KMSAN.
Rejecting the filter in the control path (at tc filter add time) is not feasible because TC filter blocks can be shared between arbitrary devices -- a filter installed on an Ethernet device may later classify packets on a headerless device through a shared block. The device association is not fixed at filter creation time.
Fix this by gating the memcpy on dev->type == ARPHRD_ETHER, which ensures only true Ethernet-framed packets have their addresses read. This is more precise than the previous hard_header_len >= 12 check, which would incorrectly pass for non-Ethernet link types like IPoIB (ARPHRD_INFINIBAND, hard_header_len=24) and FDDI (hard_header_len=21) whose L2 headers are not in Ethernet format. Additionally check skb_mac_header_was_set() to guard against the pathological case where mac_header is the unset sentinel (~0U), which would cause eth_hdr() to return a wild pointer.
For the act_mirred redirect case (Ethernet packet redirected to a non-Ethernet device sharing a TC block), zeroing the key is the correct behavior: the packet is now being classified on the target device, where Ethernet address matching is not semantically meaningful.
Note: on non-Ethernet devices, the zeroed key will match a filter configured with all-zero MAC addresses. This is an improvement over the previous behavior where uninitialized memory could randomly match any filter.
{
"affected": [],
"aliases": [
"CVE-2026-72444"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-15T06:22:18Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nflow_dissector: check device type before reading ETH_ADDRS\n\n__skb_flow_dissect() unconditionally reads 12 bytes from eth_hdr(skb)\nwhen FLOW_DISSECTOR_KEY_ETH_ADDRS is requested. This assumes the skb\nhas a valid Ethernet header at mac_header, which is not always the case.\n\nThe problem can be triggered by:\n 1. Creating a TUN device in L3 mode (IFF_TUN, hard_header_len=0)\n 2. Attaching a multiq qdisc with a flower filter matching on eth_src\n 3. Sending a packet through AF_PACKET\n\nSince TUN in L3 mode has no link-layer header, mac_header points to\nthe L3 data area. The flow dissector reads 12 bytes of uninitialized\nskb memory, which then propagates through fl_set_masked_key() and is\nused as a rhashtable lookup key in __fl_lookup(), as reported by KMSAN.\n\nRejecting the filter in the control path (at tc filter add time) is\nnot feasible because TC filter blocks can be shared between arbitrary\ndevices -- a filter installed on an Ethernet device may later classify\npackets on a headerless device through a shared block. The device\nassociation is not fixed at filter creation time.\n\nFix this by gating the memcpy on dev-\u003etype == ARPHRD_ETHER, which\nensures only true Ethernet-framed packets have their addresses read.\nThis is more precise than the previous hard_header_len \u003e= 12 check,\nwhich would incorrectly pass for non-Ethernet link types like IPoIB\n(ARPHRD_INFINIBAND, hard_header_len=24) and FDDI (hard_header_len=21)\nwhose L2 headers are not in Ethernet format. Additionally check\nskb_mac_header_was_set() to guard against the pathological case where\nmac_header is the unset sentinel (~0U), which would cause eth_hdr() to\nreturn a wild pointer.\n\nFor the act_mirred redirect case (Ethernet packet redirected to a\nnon-Ethernet device sharing a TC block), zeroing the key is the correct\nbehavior: the packet is now being classified on the target device, where\nEthernet address matching is not semantically meaningful.\n\nNote: on non-Ethernet devices, the zeroed key will match a filter\nconfigured with all-zero MAC addresses. This is an improvement over the\nprevious behavior where uninitialized memory could randomly match any\nfilter.",
"id": "GHSA-2vpj-2c73-pm86",
"modified": "2026-08-17T06:33:30Z",
"published": "2026-08-15T06:32:24Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-72444"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/0fe6455b8e1a22414f39c07bc90a1df12b52ec74"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/594c90b197141944f25991b8314de5c26ee27a7e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/825de39f0c35a112148799b3cbe45af3766c018a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9a65860959db594dfc1820c7fdc09285fb7556bf"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/bf6e8af2c8be77489bedeae9f8a9654cb710e500"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c6d3bcb0f934d4297ac5fa1c8656ae40694fb601"
}
],
"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"
}
]
}
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