{"id":"CVE-2026-72444","state":"PUBLISHED","title":"flow_dissector: check device type before reading ETH_ADDRS","description":"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->type == ARPHRD_ETHER, which\nensures only true Ethernet-framed packets have their addresses read.\nThis is more precise than the previous hard_header_len >= 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.","publishedAt":"2026-08-15T05:56:55.229Z","updatedAt":"2026-10-16T18:55:24.524Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"67a900cc0436d74e7ff89042371760def087680d","status":"affected","lessThan":"0fe6455b8e1a22414f39c07bc90a1df12b52ec74","versionType":"git"},{"version":"67a900cc0436d74e7ff89042371760def087680d","status":"affected","lessThan":"9a65860959db594dfc1820c7fdc09285fb7556bf","versionType":"git"},{"version":"67a900cc0436d74e7ff89042371760def087680d","status":"affected","lessThan":"594c90b197141944f25991b8314de5c26ee27a7e","versionType":"git"},{"version":"67a900cc0436d74e7ff89042371760def087680d","status":"affected","lessThan":"c6d3bcb0f934d4297ac5fa1c8656ae40694fb601","versionType":"git"},{"version":"67a900cc0436d74e7ff89042371760def087680d","status":"affected","lessThan":"825de39f0c35a112148799b3cbe45af3766c018a","versionType":"git"},{"version":"67a900cc0436d74e7ff89042371760def087680d","status":"affected","lessThan":"bf6e8af2c8be77489bedeae9f8a9654cb710e500","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/core/flow_dissector.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.2","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.2","versionType":"semver"},{"version":"6.1.178","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.145","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.97","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.40","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/core/flow_dissector.c"]}],"references":["https://git.kernel.org/stable/c/0fe6455b8e1a22414f39c07bc90a1df12b52ec74","https://git.kernel.org/stable/c/9a65860959db594dfc1820c7fdc09285fb7556bf","https://git.kernel.org/stable/c/594c90b197141944f25991b8314de5c26ee27a7e","https://git.kernel.org/stable/c/c6d3bcb0f934d4297ac5fa1c8656ae40694fb601","https://git.kernel.org/stable/c/825de39f0c35a112148799b3cbe45af3766c018a","https://git.kernel.org/stable/c/bf6e8af2c8be77489bedeae9f8a9654cb710e500"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/72xxx/CVE-2026-72444.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-72444","state":"PUBLISHED","datePublished":"2026-08-15T05:56:55.229Z","dateUpdated":"2026-10-16T18:55:24.524Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-09T03:40:39.930Z"},"containers":{"cna":{"title":"flow_dissector: check device type before reading ETH_ADDRS","descriptions":[{"lang":"en","value":"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->type == ARPHRD_ETHER, which\nensures only true Ethernet-framed packets have their addresses read.\nThis is more precise than the previous hard_header_len >= 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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"67a900cc0436d74e7ff89042371760def087680d","status":"affected","lessThan":"0fe6455b8e1a22414f39c07bc90a1df12b52ec74","versionType":"git"},{"version":"67a900cc0436d74e7ff89042371760def087680d","status":"affected","lessThan":"9a65860959db594dfc1820c7fdc09285fb7556bf","versionType":"git"},{"version":"67a900cc0436d74e7ff89042371760def087680d","status":"affected","lessThan":"594c90b197141944f25991b8314de5c26ee27a7e","versionType":"git"},{"version":"67a900cc0436d74e7ff89042371760def087680d","status":"affected","lessThan":"c6d3bcb0f934d4297ac5fa1c8656ae40694fb601","versionType":"git"},{"version":"67a900cc0436d74e7ff89042371760def087680d","status":"affected","lessThan":"825de39f0c35a112148799b3cbe45af3766c018a","versionType":"git"},{"version":"67a900cc0436d74e7ff89042371760def087680d","status":"affected","lessThan":"bf6e8af2c8be77489bedeae9f8a9654cb710e500","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/core/flow_dissector.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.2","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.2","versionType":"semver"},{"version":"6.1.178","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.145","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.97","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.40","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/core/flow_dissector.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/0fe6455b8e1a22414f39c07bc90a1df12b52ec74"},{"url":"https://git.kernel.org/stable/c/9a65860959db594dfc1820c7fdc09285fb7556bf"},{"url":"https://git.kernel.org/stable/c/594c90b197141944f25991b8314de5c26ee27a7e"},{"url":"https://git.kernel.org/stable/c/c6d3bcb0f934d4297ac5fa1c8656ae40694fb601"},{"url":"https://git.kernel.org/stable/c/825de39f0c35a112148799b3cbe45af3766c018a"},{"url":"https://git.kernel.org/stable/c/bf6e8af2c8be77489bedeae9f8a9654cb710e500"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The bug is hit from TC flower classification (fl_classify) on packets injected locally via AF_PACKET through an L3 TUN with mq/flower qdisc; per kernel guidance TC/netlink qdisc paths are Local, not remotely reachable network stack handlers.\nAC:L - Syzbot and the fix commit show reliable reproduction by creating an L3 TUN, attaching a multiq qdisc with a flower eth_src filter, and sending packets via AF_PACKET; the attacker controls every setup step with no races or rare kernel config.\nPR:L - Exploitation requires CAP_NET_ADMIN to create/configure the TUN and install TC flower filters via rtnetlink, plus CAP_NET_RAW for AF_PACKET sockets; both capabilities are obtainable by an unprivileged user inside a user+network namespace (unshare -Urn).\nUI:N - No victim user action is required; exploitation uses attacker-controlled local syscalls (TUN ioctl, rtnetlink TC setup, AF_PACKET sendmsg) in a namespace they create.\nS:U - Impact stays within the kernel networking/TC subsystem of the host or attacker-controlled namespace; it does not cross VM, sandbox, or IOMMU security boundaries.\nC:H - __skb_flow_dissect copies 12 bytes from eth_hdr(skb) when FLOW_DISSECTOR_KEY_ETH_ADDRS is set; on headerless devices (L3 TUN, ARPHRD_NONE) mac_header points at L3 data or unset headroom, leaking uninitialized or out-of-bounds kernel memory into flow keys used by __fl_lookup.\nI:H - Garbage eth address keys flow through fl_set_masked_key into rhashtable lookup and can spuriously match flower filters, invoking unintended TC actions (police drop, skb mark, act_mirred redirect) that alter packet handling beyond the attacker's own data.\nA:H - When mac_header is the unset sentinel (~0U), eth_hdr() becomes a wild pointer and the memcpy can page-fault with a kernel oops/panic; even without fault, mis-matched filters can apply drop/redirect actions that deny or disrupt packet delivery."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-17T05:44:16.441Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.2","versionEndExcluding":"6.1.178"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.2","versionEndExcluding":"6.6.145"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.2","versionEndExcluding":"6.12.97"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.2","versionEndExcluding":"6.18.40"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.2","versionEndExcluding":"7.1.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.2","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-72444","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T18:50:08.470597Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T18:55:24.524Z"}}]}}}