CVE-2026-98968amt: send the relay's General Query directly from the receive path

Description

In the Linux kernel, the following vulnerability has been resolved: amt: send the relay's General Query directly from the receive path An skb queued in a qdisc can outlive the tunnel it references through a raw pointer in skb->cb. For example, with igmp_qrv set to 1 on the relay a tunnel lives for 135s, so a netem delay of 180s on the amt device outlives it; when the tunnel expires and is freed, the subsequent dequeue triggers a use-after-free in amt_dev_xmit(). BUG: KASAN: slab-use-after-free in amt_dev_xmit+0x2763/0x2e20 Call Trace: amt_dev_xmit+0x2763/0x2e20 [drivers/net/amt.c:1262] dev_hard_start_xmit+0x22f/0x620 sch_direct_xmit+0x12e/0xac0 netem_dequeue+0x333/0xc50 net_tx_action+0x35c/0xa60 amt_send_igmp_gq() and amt_send_mld_gq() are only called from amt_request_handler(), inside the rcu_read_lock_bh() section of amt_rcv(). amt_request_handler() already has the tunnel the query is for: it found or created it inside that section. Queuing the query with dev_queue_xmit() only leads back into amt_dev_xmit(), which strips the Ethernet header and calls amt_send_membership_query() for that tunnel. Make that call directly from the two senders instead, the same way amt_send_advertisement() transmits from the receive path. The query never waits in a qdisc, the tunnel is only dereferenced inside the RCU section that found or created it, and nothing is stored in skb->cb, so no lookup or refcount is needed. Remove the query branch of amt_dev_xmit(), amt_skb_cb() and struct amt_skb_cb, which have no users left. Behaviour changes: - The relay's own General Queries no longer pass through the amt device's egress path: its qdisc, tc egress (clsact/tcx), the netfilter egress hook and packet taps. They are still visible as UDP on the underlay. - A query that is sent successfully is no longer counted as tx_dropped. The old query branch left through the unlock label, which counted every sent query as dropped. - A query that reaches amt_dev_xmit() on a relay from elsewhere, such as a userspace querier, is now dropped at the IGMP/MLD type switch. Before, it trusted whatever skb->cb held, and a NULL tunnel hit the WARN_ON(1).

Timeline

Scores

EPSS (exploitation in 30 days)

0.53% · top 55% of all CVEs (13 Nov 2026)

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.1.

Affected products

• Linux · Linux

  • affected cbc21dc1cfe949e37b2a54c71511579f1899e8d4 – < 423a46053788ec4a021d57e69d66db7f7f550da4
  • affected cbc21dc1cfe949e37b2a54c71511579f1899e8d4 – < 95114e421196250e3d9662f12df442799477d3c3
  • affected cbc21dc1cfe949e37b2a54c71511579f1899e8d4 – < e7183b7d518ce8b3e1f7284f9881d7a87569df14
  • affected cbc21dc1cfe949e37b2a54c71511579f1899e8d4 – < 181cb48c1e9af6b402567e132f879f89d1c54131
  • affected cbc21dc1cfe949e37b2a54c71511579f1899e8d4 – < e7ea63b4195a150604993044ab574d8240f2a399
  • affected cbc21dc1cfe949e37b2a54c71511579f1899e8d4 – < afae89de73dd693cfa329580ba0fba63bd3f0a11

• Linux · Linux

  • affected 5.16
  • unaffected < 5.16
  • unaffected 6.1.191 – ≤ 6.1.*
  • unaffected 6.6.160 – ≤ 6.6.*
  • unaffected 6.12.113 – ≤ 6.12.*
  • unaffected 6.18.57 – ≤ 6.18.*
  • unaffected 7.2.11 – ≤ 7.2.*
  • unaffected 7.3 – ≤ *

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2026-108762 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-98968](https://cveledger.app/badge/CVE-2026-98968.svg)](https://cveledger.app/cve/CVE-2026-98968)

Record last updated 30 Oct 2026, 12:40 UTC.