# CVE-2026-23074: net/sched: Enforce that teql can only be used as root qdisc > A use-after-free vulnerability in the Linux kernel's teql qdisc allows local attackers to execute arbitrary code or escalate privileges when teql is used as a child qdisc. - **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`) - **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:** 4 Feb 2026 - **Updated:** 19 Oct 2026 - **Also known as:** AZL-77238, BELL-CVE-2026-23074, DEBIAN-CVE-2026-23074, GHSA-7cwq-2xv8-7cqw, RHSA-2026:3810, ROOT-OS-DEBIAN-11-CVE-2026-23074, ROOT-OS-DEBIAN-12-CVE-2026-23074, ROOT-OS-DEBIAN-13-CVE-2026-23074, ROOT-OS-UBUNTU-2204-CVE-2026-23074, ROOT-OS-UBUNTU-2404-CVE-2026-23074 ## What is CVE-2026-23074? CVE-2026-23074 is a high-severity use after free vulnerability in Linux kernel, published on 4 Feb 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: Enforce that teql can only be used as root qdisc Design intent of teql is that it is only supposed to be used as root qdisc. We need to check for that constraint. Although not important, I will describe the scenario that unearthed this issue for the curious. GangMin Kim managed to concot a scenario as follows: ROOT qdisc 1:0 (QFQ) ├── class 1:1 (weight=15, lmax=16384) netem with delay 6.4s └── class 1:2 (weight=1, lmax=1514) teql GangMin sends a packet which is enqueued to 1:1 (netem). Any invocation of dequeue by QFQ from this class will not return a packet until after 6.4s. In the meantime, a second packet is sent and it lands on 1:2. teql's enqueue will return success and this will activate class 1:2. Main issue is that teql only updates the parent visible qlen (sch->q.qlen) at dequeue. Since QFQ will only call dequeue if peek succeeds (and teql's peek always returns NULL), dequeue will never be called and thus the qlen will remain as 0. With that in mind, when GangMin updates 1:2's lmax value, the qfq_change_class calls qfq_deact_rm_from_agg. Since the child qdisc's qlen was not incremented, qfq fails to deactivate the class, but still frees its pointers from the aggregate. So when the first packet is rescheduled after 6.4 seconds (netem's delay), a dangling pointer is accessed causing GangMin's causing a UAF. Weakness: CWE-825 (Expired Pointer Dereference), CWE-416 (Use After Free) ## Which versions are affected by CVE-2026-23074? It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `kernel` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-abi-whitelists` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-debug` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-debug-debuginfo` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-debug-devel` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-debuginfo` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-debuginfo-common-i686` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-debuginfo-common-s390x` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-debuginfo-common-x86_64` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-devel` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-doc` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-firmware` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-kdump` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-kdump-debuginfo` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `kernel-kdump-devel` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `perf` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `perf-debuginfo` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `python-perf` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | | `python-perf-debuginfo` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.59.1.el6 | Products: Linux kernel. ## How do I fix CVE-2026-23074? Apply the vendor's patch. ## Is CVE-2026-23074 being exploited? There is no known exploitation of CVE-2026-23074 in the wild and no public exploit code. ## Other vulnerabilities in Linux kernel - [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild) - [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild) - [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild) - [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild) - [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-23074 and fix it if it is affected. What it is: CVE-2026-23074 is a high-severity use after free vulnerability in Linux kernel, published on 4 Feb 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-2026-23074 in the wild and no public exploit code. Affected product: Linux kernel. 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-2026-23074/ (Markdown: https://insights.sbomify.com/CVE-2026-23074/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23074 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23074 - OSV: https://osv.dev/vulnerability/CVE-2026-23074 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-23074/ Summaries are generated and may contain mistakes; the official description above is the record.