# CVE-2026-74266: net/sched: sch_dualpi2: Do not call qdisc_tree_reduce_backlog during peek before restoring qlen > A null pointer dereference in the Linux kernel's dualpi2 qdisc allows local attackers to cause a system crash by triggering a specific packet drop scenario. - **Severity:** Not scored - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Local or same network only - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 15 Aug 2026 - **Updated:** 17 Aug 2026 - **Also known as:** BELL-CVE-2026-74266, DEBIAN-CVE-2026-74266, GHSA-frwj-6925-xvf6, UBUNTU-CVE-2026-74266 ## What is CVE-2026-74266? CVE-2026-74266 is a vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim. ### Official description In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_dualpi2: Do not call qdisc_tree_reduce_backlog during peek before restoring qlen Whenever dualpi2 drops packets during peek, it calls qdisc_tree_reduce_backlog. An issue arises because it calls qdisc_tree_reduce_backlog before it reincrements the qlen. If qlen drops to zero, but peek returns an skb, the parent's qlen_notify callback will be executed even though dualpi2 still has 1 packet on the queue and, thus, mistakenly deactivates the parent's class which leads to a null-ptr-deref: [ 101.427314][ T599] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000009: 0000 [#1] SMP KASAN NOPTI [ 101.427755][ T599] KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f] [ 101.428048][ T599] CPU: 2 UID: 0 PID: 599 Comm: ping Not tainted 7.1.0-rc5-00284-gbce53c430ed7 #102 PREEMPT(full) [ 101.428400][ T599] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 101.428608][ T599] RIP: 0010:qfq_dequeue (net/sched/sch_qfq.c:1150) sch_qfq [ 101.428821][ T599] Code: 00 fc ff df 80 3c 02 00 0f 85 46 0c 00 00 4c 8d 73 48 48 89 9d b8 02 00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 f2 48 c1 ea 03 <80> 3c 02 00 0f 85 2d 0c 00 00 48 b8 00 00 00 00 00 fc ff df 4c 8b All code [ 101.429348][ T599] RSP: 0018:ffff8881110df4f0 EFLAGS: 00010216 [ 101.429541][ T599] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: dffffc0000000000 [ 101.429763][ T599] RDX: 0000000000000009 RSI: 00000024c0000000 RDI: ffff88811436c2b0 [ 101.429985][ T599] RBP: ffff88811436c000 R08: ffff88811436c280 R09: 1ffff11021277523 [ 101.430206][ T599] R10: 1ffff11021277526 R11: 1ffff11021277527 R12: 00000024c0000000 [ 101.430423][ T599] R13: ffff88811436c2b8 R14: 0000000000000048 R15: 0000000020000000 [ 101.430642][ T599] FS: 00007f61813e1c40(0000) GS:ffff8881691ef000(0000) knlGS:0000000000000000 [ 101.430913][ T599] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 101.431100][ T599] CR2: 00005651650850a8 CR3: 000000010ca0b000 CR4: 0000000000750ef0 [ 101.431320][ T599] PKRU: 55555554 [ 101.431433][ T599] Call Trace: [ 101.431544][ T599] [ 101.431628][ T599] __qdisc_run (net/sched/sch_generic.c:322 net/sched/sch_generic.c:427 net/sched/sch_generic.c:445) [ 101.431792][ T599] ? dev_qdisc_enqueue (./include/trace/events/qdisc.h:49 (discriminator 22) net/core/dev.c:4176 (discriminator 22)) [ 101.431941][ T599] __dev_queue_xmit (./include/net/pkt_sched.h:120 ./include/net/pkt_sched.h:117 net/core/dev.c:4292 net/core/dev.c:4831) Fix this by only calling qdisc_tree_reduce_backlog in peek after the qlen is restored. ## Which versions are affected by CVE-2026-74266? ## How do I fix CVE-2026-74266? Apply the vendor's patch. ## Is CVE-2026-74266 being exploited? There is no known exploitation of CVE-2026-74266 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-74266 and fix it if it is affected. What it is: CVE-2026-74266 is a vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-74266 in the wild and no public exploit code. Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-74266/ (Markdown: https://insights.sbomify.com/CVE-2026-74266/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74266 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74266 - OSV: https://osv.dev/vulnerability/CVE-2026-74266 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-74266/ Summaries are generated and may contain mistakes; the official description above is the record.