{"id":"CVE-2026-98968","title":"amt: send the relay's General Query directly from the receive path","summary":"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 …","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= cbc21dc1cfe949e37b2a54c71511579f1899e8d4 < 95114e421196250e3d9662f12df442799477d3c3","Linux >= cbc21dc1cfe949e37b2a54c71511579f1899e8d4 < e7183b7d518ce8b3e1f7284f9881d7a87569df14","Linux >= cbc21dc1cfe949e37b2a54c71511579f1899e8d4 < 181cb48c1e9af6b402567e132f879f89d1c54131","Linux >= cbc21dc1cfe949e37b2a54c71511579f1899e8d4 < e7ea63b4195a150604993044ab574d8240f2a399","Linux >= cbc21dc1cfe949e37b2a54c71511579f1899e8d4 < afae89de73dd693cfa329580ba0fba63bd3f0a11","Linux 5.16"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T12:19:39.236Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98968","references":[{"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"}],"tags":["cve.org"],"ingestedAt":"2026-10-23T13:24:55.553Z","slug":"CVE-2026-98968","body":"## Overview\n\nIn 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).\n\n## Affected\n\n- `Linux >= cbc21dc1cfe949e37b2a54c71511579f1899e8d4 < 95114e421196250e3d9662f12df442799477d3c3`\n- `Linux >= cbc21dc1cfe949e37b2a54c71511579f1899e8d4 < e7183b7d518ce8b3e1f7284f9881d7a87569df14`\n- `Linux >= cbc21dc1cfe949e37b2a54c71511579f1899e8d4 < 181cb48c1e9af6b402567e132f879f89d1c54131`\n- `Linux >= cbc21dc1cfe949e37b2a54c71511579f1899e8d4 < e7ea63b4195a150604993044ab574d8240f2a399`\n- `Linux >= cbc21dc1cfe949e37b2a54c71511579f1899e8d4 < afae89de73dd693cfa329580ba0fba63bd3f0a11`\n- `Linux 5.16`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}