CVE-2026-98968
Received
Received - Intake
Use-After-Free in Linux Kernel AMT Module
Vulnerability report for CVE-2026-98968, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-10-23
Last updated on: 2026-10-23
Assigner: kernel.org
Description
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).
CVSS Scores
EPSS Scores
| Probability: | |
| Percentile: |
Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| Linux | Linux | cbc21dc1cfe949e37b2a54c71511579f1899e8d4 |
| Linux | Linux | cbc21dc1cfe949e37b2a54c71511579f1899e8d4 |
| Linux | Linux | cbc21dc1cfe949e37b2a54c71511579f1899e8d4 |
| Linux | Linux | cbc21dc1cfe949e37b2a54c71511579f1899e8d4 |
| Linux | Linux | cbc21dc1cfe949e37b2a54c71511579f1899e8d4 |
| Linux | Linux | 5.16 |
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-UNKNOWN |
