# CVE-2023-4623: Use-after-free in Linux kernel's net/sched: sch_hfsc (HFSC qdisc traffic control) component > A use-after-free in the Linux kernel's HFSC qdisc allows local attackers to escalate privileges. - **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:** 6 Sep 2023 - **Updated:** 14 Oct 2026 - **Also known as:** AZL-31697, BELL-CVE-2023-4623, DEBIAN-CVE-2023-4623, GHSA-j8c5-g64v-xj97, RHSA-2024:1747, SUSE-SU-2023:4164-1, SUSE-SU-2023:4204-1, SUSE-SU-2023:4208-1, SUSE-SU-2023:4244-1, SUSE-SU-2023:4278-1, SUSE-SU-2023:4300-1, SUSE-SU-2023:4313-1, SUSE-SU-2023:4321-1, SUSE-SU-2023:4328-1, UBUNTU-CVE-2023-4623 ## What is CVE-2023-4623? CVE-2023-4623 is a high-severity use after free vulnerability in Debian Debian Linux, published on 6 Sep 2023. It can only be exploited from the same machine or local network, with no action from the victim. ### Official description A use-after-free vulnerability in the Linux kernel's net/sched: sch_hfsc (HFSC qdisc traffic control) component can be exploited to achieve local privilege escalation. If a class with a link-sharing curve (i.e. with the HFSC_FSC flag set) has a parent without a link-sharing curve, then init_vf() will call vttree_insert() on the parent, but vttree_remove() will be skipped in update_vf(). This leaves a dangling pointer that can cause a use-after-free. We recommend upgrading past commit b3d26c5702c7d6c45456326e56d2ccf3f103e60f. Weakness: CWE-416 (Use After Free) ## Which versions are affected by CVE-2023-4623? It affects 2 products. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `bpftool` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel-abi-whitelists` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel-debug` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel-debug-debuginfo` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel-debug-devel` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel-debuginfo` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel-debuginfo-common-x86_64` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel-devel` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel-doc` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel-tools` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel-tools-debuginfo` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel-tools-libs` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kernel-tools-libs-devel` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `perf` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `perf-debuginfo` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `python-perf` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `python-perf-debuginfo` | Red Hat:rhel_aus:7.6::server | All versions | 0:3.10.0-957.112.1.el7 | | `kgraft-patch-SLE12-SP5_Update_36` | SUSE:Linux Enterprise Live Patching 12 SP5 | All versions | 12-2.3 | | `kgraft-patch-SLE12-SP5_Update_42` | SUSE:Linux Enterprise Live Patching 12 SP5 | All versions | 7-2.2 | | `kgraft-patch-SLE12-SP5_Update_43` | SUSE:Linux Enterprise Live Patching 12 SP5 | All versions | 6-2.2 | | `kgraft-patch-SLE12-SP5_Update_44` | SUSE:Linux Enterprise Live Patching 12 SP5 | All versions | 5-2.2 | | `kgraft-patch-SLE12-SP5_Update_45` | SUSE:Linux Enterprise Live Patching 12 SP5 | All versions | 4-2.2 | | `kgraft-patch-SLE12-SP5_Update_47` | SUSE:Linux Enterprise Live Patching 12 SP5 | All versions | 3-2.2 | | `kernel-livepatch-SLE15-SP1_Update_35` | SUSE:Linux Enterprise Live Patching 15 SP1 | All versions | 12-150100.2.3 | | `kernel-livepatch-SLE15-SP1_Update_36` | SUSE:Linux Enterprise Live Patching 15 SP1 | All versions | 10-150100.2.3 | | `kernel-livepatch-SLE15-SP1_Update_41` | SUSE:Linux Enterprise Live Patching 15 SP1 | All versions | 5-150100.2.2 | | `kernel-livepatch-SLE15-SP1_Update_42` | SUSE:Linux Enterprise Live Patching 15 SP1 | All versions | 4-150100.2.2 | | `kernel-livepatch-SLE15-SP2_Update_39` | SUSE:Linux Enterprise Live Patching 15 SP2 | All versions | 3-150200.2.1 | | `kernel-livepatch-SLE15-SP4-RT_Update_13` | SUSE:Linux Enterprise Live Patching 15 SP4 | All versions | 2-150400.2.1 | | `kernel-livepatch-SLE15-SP4_Update_18` | SUSE:Linux Enterprise Live Patching 15 SP4 | All versions | 2-150400.2.1 | | `kernel-livepatch-SLE15-SP5-RT_Update_5` | SUSE:Linux Enterprise Live Patching 15 SP5 | All versions | 2-150500.2.1 | | `kernel-livepatch-SLE15-SP5_Update_5` | SUSE:Linux Enterprise Live Patching 15 SP5 | All versions | 2-150500.2.1 | Products: Debian Debian Linux, Linux kernel. ## How do I fix CVE-2023-4623? Apply the vendor's patch. ## Is CVE-2023-4623 being exploited? There is no known exploitation of CVE-2023-4623 in the wild and no public exploit code. ## Other vulnerabilities in Debian Debian Linux - [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild) - [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild) - [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild) - [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild) - [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2023-4623 and fix it if it is affected. What it is: CVE-2023-4623 is a high-severity use after free vulnerability in Debian Debian Linux, published on 6 Sep 2023. 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-2023-4623 in the wild and no public exploit code. Affected product: Debian Debian 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-2023-4623/ (Markdown: https://insights.sbomify.com/CVE-2023-4623/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2023-4623 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-4623 - OSV: https://osv.dev/vulnerability/CVE-2023-4623 --- From sbomify Insights: https://insights.sbomify.com/CVE-2023-4623/ Summaries are generated and may contain mistakes; the official description above is the record.