# CVE-2026-43496: net/sched: sch_red: Replace direct dequeue call with peek and qdisc_dequeue_peeked

Status: published. Published: 2026-05-21. Updated: 2026-11-06.

In the Linux kernel, the following vulnerability has been resolved:

net/sched: sch_red: Replace direct dequeue call with peek and qdisc_dequeue_peeked

When red qdisc has children (eg qfq qdisc) whose peek() callback is
qdisc_peek_dequeued(), we could get a kernel panic. When the parent of such
qdiscs (eg illustrated in patch #3 as tbf) wants to retrieve an skb from
its child (red in this case), it will do the following:
 1a. do a peek() - and when sensing there's an skb the child can offer, then
     - the child in this case(red) calls its child's (qfq) peek.
        qfq does the right thing and will return the gso_skb queue packet.
        Note: if there wasnt a gso_skb entry then qfq will store it there.
 1b. invoke a dequeue() on the child (red). And herein lies the problem.
     - red will call the child's dequeue() which will essentially just
       try to grab something of qfq's queue.

[   78.667668][  T363] KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f]
[   78.667927][  T363] CPU: 1 UID: 0 PID: 363 Comm: ping Not tainted 7.1.0-rc1-00033-g46f74a3f7d57-dirty #790 PREEMPT(full)
[   78.668263][  T363] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   78.668486][  T363] RIP: 0010:qfq_dequeue+0x446/0xc90 [sch_qfq]
[   78.668718][  T363] Code: 54 c0 e8 dd 90 00 f1 48 c7 c7 e0 03 54 c0 48 89 de e8 ce 90 00 f1 48 8d 7b 48 b8 ff ff 37 00 48 89 fa 48 c1 e0 2a 48 c1 ea 03 <80> 3c 02 00 74 05 e8 ef a1 e1 f1 48 8b 7b 48 48 8d 54 24 58 48 8d
[   78.669312][  T363] RSP: 0018:ffff88810de573e0 EFLAGS: 00010216
[   78.669533][  T363] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
[   78.669790][  T363] RDX: 0000000000000009 RSI: 0000000000000004 RDI: 0000000000000048
[   78.670044][  T363] RBP: ffff888110dc4000 R08: ffffffffb1b0885a R09: fffffbfff6ba9078
[   78.670297][  T363] R10: 0000000000000003 R11: ffff888110e31c80 R12: 0000001880000000
[   78.670560][  T363] R13: ffff888110dc4150 R14: ffff888110dc42b8 R15: 0000000000000200
[   78.670814][  T363] FS:  00007f66a8f09c40(0000) GS:ffff888163428000(0000) knlGS:0000000000000000
[   78.671110][  T363] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   78.671324][  T363] CR2: 000055db4c6a30a8 CR3: 000000010da67000 CR4: 0000000000750ef0
[   78.671585][  T363] PKRU: 55555554
[   78.671713][  T363] Call Trace:
[   78.671843][  T363]  <TASK>
[   78.671936][  T363]  ? __pfx_qfq_dequeue+0x10/0x10 [sch_qfq]
[   78.672148][  T363]  ? __pfx__printk+0x10/0x10
[   78.672322][  T363]  ? srso_alias_return_thunk+0x5/0xfbef5
[   78.672496][  T363]  ? lockdep_hardirqs_on_prepare+0xa8/0x1a0
[   78.672706][  T363]  ? srso_alias_return_thunk+0x5/0xfbef5
[   78.672875][  T363]  ? trace_hardirqs_on+0x19/0x1a0
[   78.673047][  T363]  red_dequeue+0x65/0x270 [sch_red]
[   78.673217][  T363]  ? srso_alias_return_thunk+0x5/0xfbef5
[   78.673385][  T363]  tbf_dequeue.cold+0xb0/0x70c [sch_tbf]
[   78.673566][  T363]  __qdisc_run+0x169/0x1900

The right thing to do in #1b is to grab the skb off gso_skb queue.
This patchset fixes that issue by changing #1b to use qdisc_dequeue_peeked()
method instead.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 77be155cba4e163e8bba9fd27222a8b6189ec4f7; < 03b0aaeba082ae981a0dfe96cdd03d02050537a1 (affected, git); ≥ 77be155cba4e163e8bba9fd27222a8b6189ec4f7; < c7335f4dc0fa21f7015b910c6fc2f4d599732328 (affected, git); ≥ 77be155cba4e163e8bba9fd27222a8b6189ec4f7; < 45cd83c5c470ba49fe261489c8358ad7b9df7c45 (affected, git); ≥ 77be155cba4e163e8bba9fd27222a8b6189ec4f7; < 36aa34f42cb6842cf371f3a2d3e855d24fd57a50 (affected, git); ≥ 77be155cba4e163e8bba9fd27222a8b6189ec4f7; < ce051eede433f876d322ac3550a36a3c6fc4c231 (affected, git); ≥ 77be155cba4e163e8bba9fd27222a8b6189ec4f7; < 8d09618840b99ef00154d3e731ce9b11e096196d (affected, git); ≥ 77be155cba4e163e8bba9fd27222a8b6189ec4f7; < 587dcf970a525f543d8b5855d9f37a4ca97b76ef (affected, git); ≥ 77be155cba4e163e8bba9fd27222a8b6189ec4f7; < 458d5615272d3de535748342eb68ca492343048c (affected, git). Source: CNA: Linux
- Linux / Linux: 2.6.29 (affected); ≥ 0; < 2.6.29 (unaffected, semver); ≥ 5.10.258; ≤ 5.10.* (unaffected, semver); ≥ 5.15.209; ≤ 5.15.* (unaffected, semver); ≥ 6.1.175; ≤ 6.1.* (unaffected, semver); ≥ 6.6.140; ≤ 6.6.* (unaffected, semver); ≥ 6.12.88; ≤ 6.12.* (unaffected, semver); ≥ 6.18.30; ≤ 6.18.* (unaffected, semver); ≥ 7.0.7; ≤ 7.0.* (unaffected, semver); ≥ 7.1; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux
- Siemens / SIMATIC S7-1500 TM MFP - GNU/Linux subsystem: ≥ 0; < * (affected, custom). Source: ADP: siemens-SADP

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.12% as of 2026-11-06; percentile 1.93%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/03b0aaeba082ae981a0dfe96cdd03d02050537a1 (CNA: Linux)

- https://git.kernel.org/stable/c/c7335f4dc0fa21f7015b910c6fc2f4d599732328 (CNA: Linux)

- https://git.kernel.org/stable/c/45cd83c5c470ba49fe261489c8358ad7b9df7c45 (CNA: Linux)

- https://git.kernel.org/stable/c/36aa34f42cb6842cf371f3a2d3e855d24fd57a50 (CNA: Linux)

- https://git.kernel.org/stable/c/ce051eede433f876d322ac3550a36a3c6fc4c231 (CNA: Linux)

- https://git.kernel.org/stable/c/8d09618840b99ef00154d3e731ce9b11e096196d (CNA: Linux)

- https://git.kernel.org/stable/c/587dcf970a525f543d8b5855d9f37a4ca97b76ef (CNA: Linux)

- https://git.kernel.org/stable/c/458d5615272d3de535748342eb68ca492343048c (CNA: Linux)

- https://cert-portal.siemens.com/productcert/html/ssa-784472.html (ADP: siemens-SADP)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-43496; retrieved 2026-11-06; source updated 2026-11-06

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-43496; retrieved 2026-11-06; source updated Not reported

Revision: 2f46111d3578ce450e9c9abc82de9aaa2fcfe000fd5324b20207a9df72f80893

Canonical: https://y2.dev/cve/CVE-2026-43496

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