{"cve":"CVE-2026-23340","nvd":{"published":"2026-03-25T11:16:31.837","modified":"2026-10-19T19:17:45.897","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: sched: avoid qdisc_reset_all_tx_gt() vs dequeue race for lockless qdiscs\n\nWhen shrinking the number of real tx queues,\nnetif_set_real_num_tx_queues() calls qdisc_reset_all_tx_gt() to flush\nqdiscs for queues which will no longer be used.\n\nqdisc_reset_all_tx_gt() currently serializes qdisc_reset() with\nqdisc_lock(). However, for lockless qdiscs, the dequeue path is\nserialized by qdisc_run_begin/end() using qdisc->seqlock instead, so\nqdisc_reset() can run concurrently with __qdisc_run() and free skbs\nwhile they are still being dequeued, leading to UAF.\n\nThis can easily be reproduced on e.g. virtio-net by imposing heavy\ntraffic while frequently changing the number of queue pairs:\n\n  iperf3 -ub0 -c $peer -t 0 &\n  while :; do\n    ethtool -L eth0 combined 1\n    ethtool -L eth0 combined 2\n  done\n\nWith KASAN enabled, this leads to reports like:\n\n  BUG: KASAN: slab-use-after-free in __qdisc_run+0x133f/0x1760\n  ...\n  Call Trace:\n   <TASK>\n   ...\n   __qdisc_run+0x133f/0x1760\n   __dev_queue_xmit+0x248f/0x3550\n   ip_finish_output2+0xa42/0x2110\n   ip_output+0x1a7/0x410\n   ip_send_skb+0x2e6/0x480\n   udp_send_skb+0xb0a/0x1590\n   udp_sendmsg+0x13c9/0x1fc0\n   ...\n   </TASK>\n\n  Allocated by task 1270 on cpu 5 at 44.558414s:\n   ...\n   alloc_skb_with_frags+0x84/0x7c0\n   sock_alloc_send_pskb+0x69a/0x830\n   __ip_append_data+0x1b86/0x48c0\n   ip_make_skb+0x1e8/0x2b0\n   udp_sendmsg+0x13a6/0x1fc0\n   ...\n\n  Freed by task 1306 on cpu 3 at 44.558445s:\n   ...\n   kmem_cache_free+0x117/0x5e0\n   pfifo_fast_reset+0x14d/0x580\n   qdisc_reset+0x9e/0x5f0\n   netif_set_real_num_tx_queues+0x303/0x840\n   virtnet_set_channels+0x1bf/0x260 [virtio_net]\n   ethnl_set_channels+0x684/0xae0\n   ethnl_default_set_doit+0x31a/0x890\n   ...\n\nSerialize qdisc_reset_all_tx_gt() against the lockless dequeue path by\ntaking qdisc->seqlock for TCQ_F_NOLOCK qdiscs, matching the\nserialization model already used by dev_reset_queue().\n\nAdditionally clear QDISC_STATE_NON_EMPTY after reset so the qdisc state\nreflects an empty queue, avoiding needless re-scheduling.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.8},"cwes":["CWE-416","CWE-362"],"references":["https://git.kernel.org/stable/c/5bb27ad54d12de67e457d7d251198e361bef835e","https://git.kernel.org/stable/c/5bc4e69306ed7ae02232eb4c0b23ed621a26d504","https://git.kernel.org/stable/c/7594467c49bfc2f4644dee0415ac2290db11fa0d","https://git.kernel.org/stable/c/7f083faf59d14c04e01ec05a7507f036c965acf8","https://git.kernel.org/stable/c/8314944cc3bdeaa5a73e6f8a8cf0d94822e625cb"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-21T03:43:09.190223697+00:00"},"epss":{"cve":"CVE-2026-23340","score":0.00117,"percentile":0.01671,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}