{"id":"CVE-2026-98968","state":"PUBLISHED","title":"amt: send the relay's General Query directly from the receive path","description":"In the Linux kernel, the following vulnerability has been resolved:\n\namt: send the relay's General Query directly from the receive path\n\nAn skb queued in a qdisc can outlive the tunnel it references\nthrough a raw pointer in skb->cb. For example, with igmp_qrv set\nto 1 on the relay a tunnel lives for 135s, so a netem delay of\n180s on the amt device outlives it; when the tunnel expires and is\nfreed, the subsequent dequeue triggers a use-after-free in\namt_dev_xmit().\n\n  BUG: KASAN: slab-use-after-free in amt_dev_xmit+0x2763/0x2e20\n  Call Trace:\n   amt_dev_xmit+0x2763/0x2e20 [drivers/net/amt.c:1262]\n   dev_hard_start_xmit+0x22f/0x620\n   sch_direct_xmit+0x12e/0xac0\n   netem_dequeue+0x333/0xc50\n   net_tx_action+0x35c/0xa60\n\namt_send_igmp_gq() and amt_send_mld_gq() are only called from\namt_request_handler(), inside the rcu_read_lock_bh() section of\namt_rcv(). amt_request_handler() already has the tunnel the query is\nfor: it found or created it inside that section. Queuing the query with\ndev_queue_xmit() only leads back into amt_dev_xmit(), which strips the\nEthernet header and calls amt_send_membership_query() for that tunnel.\n\nMake that call directly from the two senders instead, the same way\namt_send_advertisement() transmits from the receive path. The query\nnever waits in a qdisc, the tunnel is only dereferenced inside the\nRCU section that found or created it, and nothing is stored in\nskb->cb, so no lookup or refcount is needed. Remove the query branch\nof amt_dev_xmit(), amt_skb_cb() and struct amt_skb_cb, which have no\nusers left.\n\nBehaviour changes:\n - The relay's own General Queries no longer pass through the amt\n   device's egress path: its qdisc, tc egress (clsact/tcx), the\n   netfilter egress hook and packet taps. They are still visible as\n   UDP on the underlay.\n - A query that is sent successfully is no longer counted as\n   tx_dropped. The old query branch left through the unlock label,\n   which counted every sent query as dropped.\n - A query that reaches amt_dev_xmit() on a relay from elsewhere,\n   such as a userspace querier, is now dropped at the IGMP/MLD type\n   switch. Before, it trusted whatever skb->cb held, and a NULL\n   tunnel hit the WARN_ON(1).","publishedAt":"2026-10-23T12:19:39.236Z","updatedAt":"2026-10-30T12:40:34.695Z","severity":{"score":8.1,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/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":"cbc21dc1cfe949e37b2a54c71511579f1899e8d4","status":"affected","lessThan":"423a46053788ec4a021d57e69d66db7f7f550da4","versionType":"git"},{"version":"cbc21dc1cfe949e37b2a54c71511579f1899e8d4","status":"affected","lessThan":"95114e421196250e3d9662f12df442799477d3c3","versionType":"git"},{"version":"cbc21dc1cfe949e37b2a54c71511579f1899e8d4","status":"affected","lessThan":"e7183b7d518ce8b3e1f7284f9881d7a87569df14","versionType":"git"},{"version":"cbc21dc1cfe949e37b2a54c71511579f1899e8d4","status":"affected","lessThan":"181cb48c1e9af6b402567e132f879f89d1c54131","versionType":"git"},{"version":"cbc21dc1cfe949e37b2a54c71511579f1899e8d4","status":"affected","lessThan":"e7ea63b4195a150604993044ab574d8240f2a399","versionType":"git"},{"version":"cbc21dc1cfe949e37b2a54c71511579f1899e8d4","status":"affected","lessThan":"afae89de73dd693cfa329580ba0fba63bd3f0a11","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/amt.c","include/net/amt.h"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.16","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.16","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.113","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.11","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/amt.c","include/net/amt.h"]}],"references":["https://git.kernel.org/stable/c/423a46053788ec4a021d57e69d66db7f7f550da4","https://git.kernel.org/stable/c/95114e421196250e3d9662f12df442799477d3c3","https://git.kernel.org/stable/c/e7183b7d518ce8b3e1f7284f9881d7a87569df14","https://git.kernel.org/stable/c/181cb48c1e9af6b402567e132f879f89d1c54131","https://git.kernel.org/stable/c/e7ea63b4195a150604993044ab574d8240f2a399","https://git.kernel.org/stable/c/afae89de73dd693cfa329580ba0fba63bd3f0a11"],"weaknesses":[],"ingestedAt":"2026-10-30T13:00:06.648Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98968.json","commit":"cb14bf1b43b0c9f05f7f40eae2246263fd430780","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98968","state":"PUBLISHED","datePublished":"2026-10-23T12:19:39.236Z","dateUpdated":"2026-10-30T12:40:34.695Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.383Z"},"containers":{"cna":{"title":"amt: send the relay's General Query directly from the receive path","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\namt: send the relay's General Query directly from the receive path\n\nAn skb queued in a qdisc can outlive the tunnel it references\nthrough a raw pointer in skb->cb. For example, with igmp_qrv set\nto 1 on the relay a tunnel lives for 135s, so a netem delay of\n180s on the amt device outlives it; when the tunnel expires and is\nfreed, the subsequent dequeue triggers a use-after-free in\namt_dev_xmit().\n\n  BUG: KASAN: slab-use-after-free in amt_dev_xmit+0x2763/0x2e20\n  Call Trace:\n   amt_dev_xmit+0x2763/0x2e20 [drivers/net/amt.c:1262]\n   dev_hard_start_xmit+0x22f/0x620\n   sch_direct_xmit+0x12e/0xac0\n   netem_dequeue+0x333/0xc50\n   net_tx_action+0x35c/0xa60\n\namt_send_igmp_gq() and amt_send_mld_gq() are only called from\namt_request_handler(), inside the rcu_read_lock_bh() section of\namt_rcv(). amt_request_handler() already has the tunnel the query is\nfor: it found or created it inside that section. Queuing the query with\ndev_queue_xmit() only leads back into amt_dev_xmit(), which strips the\nEthernet header and calls amt_send_membership_query() for that tunnel.\n\nMake that call directly from the two senders instead, the same way\namt_send_advertisement() transmits from the receive path. The query\nnever waits in a qdisc, the tunnel is only dereferenced inside the\nRCU section that found or created it, and nothing is stored in\nskb->cb, so no lookup or refcount is needed. Remove the query branch\nof amt_dev_xmit(), amt_skb_cb() and struct amt_skb_cb, which have no\nusers left.\n\nBehaviour changes:\n - The relay's own General Queries no longer pass through the amt\n   device's egress path: its qdisc, tc egress (clsact/tcx), the\n   netfilter egress hook and packet taps. They are still visible as\n   UDP on the underlay.\n - A query that is sent successfully is no longer counted as\n   tx_dropped. The old query branch left through the unlock label,\n   which counted every sent query as dropped.\n - A query that reaches amt_dev_xmit() on a relay from elsewhere,\n   such as a userspace querier, is now dropped at the IGMP/MLD type\n   switch. Before, it trusted whatever skb->cb held, and a NULL\n   tunnel hit the WARN_ON(1)."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"cbc21dc1cfe949e37b2a54c71511579f1899e8d4","status":"affected","lessThan":"423a46053788ec4a021d57e69d66db7f7f550da4","versionType":"git"},{"version":"cbc21dc1cfe949e37b2a54c71511579f1899e8d4","status":"affected","lessThan":"95114e421196250e3d9662f12df442799477d3c3","versionType":"git"},{"version":"cbc21dc1cfe949e37b2a54c71511579f1899e8d4","status":"affected","lessThan":"e7183b7d518ce8b3e1f7284f9881d7a87569df14","versionType":"git"},{"version":"cbc21dc1cfe949e37b2a54c71511579f1899e8d4","status":"affected","lessThan":"181cb48c1e9af6b402567e132f879f89d1c54131","versionType":"git"},{"version":"cbc21dc1cfe949e37b2a54c71511579f1899e8d4","status":"affected","lessThan":"e7ea63b4195a150604993044ab574d8240f2a399","versionType":"git"},{"version":"cbc21dc1cfe949e37b2a54c71511579f1899e8d4","status":"affected","lessThan":"afae89de73dd693cfa329580ba0fba63bd3f0a11","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/amt.c","include/net/amt.h"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.16","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.16","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.113","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.11","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/amt.c","include/net/amt.h"]}],"references":[{"url":"https://git.kernel.org/stable/c/423a46053788ec4a021d57e69d66db7f7f550da4"},{"url":"https://git.kernel.org/stable/c/95114e421196250e3d9662f12df442799477d3c3"},{"url":"https://git.kernel.org/stable/c/e7183b7d518ce8b3e1f7284f9881d7a87569df14"},{"url":"https://git.kernel.org/stable/c/181cb48c1e9af6b402567e132f879f89d1c54131"},{"url":"https://git.kernel.org/stable/c/e7ea63b4195a150604993044ab574d8240f2a399"},{"url":"https://git.kernel.org/stable/c/afae89de73dd693cfa329580ba0fba63bd3f0a11"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":8.1,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - A routable UDP AMT_MSG_REQUEST enters udp_rcv() and amt_rcv(), and amt_request_handler() uses its source tuple, nonce, and p bit in the patched amt_send_igmp_gq()/amt_send_mld_gq(); the resulting query later dequeues into patched amt_dev_xmit().\nAC:H - The remote attacker can send the Request and let the tunnel expire, but cannot arrange the required relay-local queue retention: the demonstrated trigger uses igmp_qrv=1 for a 135-second amt_gmi() and a 180-second netem delay. Success therefore depends on target state outside remote control.\nPR:N - The relay branch of amt_rcv() dispatches AMT_MSG_REQUEST directly to amt_request_handler(), which checks only length and reserved/version bits before creating a tunnel; it requires no Discovery state, nonce/MAC validation, credentials, or capability.\nUI:N - Once the relay and delaying qdisc exist, the attacker only sends a Request; amt_request_handler() schedules gc_wq, and amt_tunnel_expire() plus netem dequeue run without victim action.\nS:U - The freed amt_tunnel_list and the accesses from amt_dev_xmit()/amt_send_membership_query() remain within the relay host's kernel; no VM, IOMMU, or other authority boundary is crossed.\nC:H - amt_send_membership_query() reads freed tunnel->ip4, source_port, nonce, and mac, and emits the nonce and MAC in an outbound AMT Membership Query; reclaiming the slab makes this a kernel UAF disclosure primitive.\nI:H - After transmission, amt_update_relay_status() executes spin_lock_bh(&tunnel->lock) and writes tunnel->status through the freed or reallocated amt_tunnel_list, enabling kernel heap corruption and potential control-flow hijacking.\nA:H - The delayed dequeue in amt_dev_xmit() produced the reported KASAN slab-use-after-free; its stale routing, lock, and status accesses can oops, panic, or hang the kernel, and new Requests can trigger it again after tunnel expiry."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:40:34.695Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.16","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.16","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.16","versionEndExcluding":"6.12.113"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.16","versionEndExcluding":"6.18.57"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.16","versionEndExcluding":"7.2.11"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.16","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}