# CVE-2024-53044: net/sched: sch_api: fix xa_insert() error path in tcf_block_get_ext() > A logic error in the Linux kernel's traffic control subsystem causes an unrecoverable denial of service when specific qdisc commands fail, requiring a system reboot to recover. - **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:** 19 Nov 2024 - **Updated:** 5 Aug 2026 - **Also known as:** BELL-CVE-2024-53044, DEBIAN-CVE-2024-53044, GHSA-g4gg-7gqp-cf6m, UBUNTU-CVE-2024-53044 ## What is CVE-2024-53044? CVE-2024-53044 is a high-severity denial of service vulnerability in Linux kernel, published on 19 Nov 2024. 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_api: fix xa_insert() error path in tcf_block_get_ext() This command: $ tc qdisc replace dev eth0 ingress_block 1 egress_block 1 clsact Error: block dev insert failed: -EBUSY. fails because user space requests the same block index to be set for both ingress and egress. [ side note, I don't think it even failed prior to commit 913b47d3424e ("net/sched: Introduce tc block netdev tracking infra"), because this is a command from an old set of notes of mine which used to work, but alas, I did not scientifically bisect this ] The problem is not that it fails, but rather, that the second time around, it fails differently (and irrecoverably): $ tc qdisc replace dev eth0 ingress_block 1 egress_block 1 clsact Error: dsa_core: Flow block cb is busy. [ another note: the extack is added by me for illustration purposes. the context of the problem is that clsact_init() obtains the same &q->ingress_block pointer as &q->egress_block, and since we call tcf_block_get_ext() on both of them, "dev" will be added to the block->ports xarray twice, thus failing the operation: once through the ingress block pointer, and once again through the egress block pointer. the problem itself is that when xa_insert() fails, we have emitted a FLOW_BLOCK_BIND command through ndo_setup_tc(), but the offload never sees a corresponding FLOW_BLOCK_UNBIND. ] Even correcting the bad user input, we still cannot recover: $ tc qdisc replace dev swp3 ingress_block 1 egress_block 2 clsact Error: dsa_core: Flow block cb is busy. Basically the only way to recover is to reboot the system, or unbind and rebind the net device driver. To fix the bug, we need to fill the correct error teardown path which was missed during code movement, and call tcf_block_offload_unbind() when xa_insert() fails. [ last note, fundamentally I blame the label naming convention in tcf_block_get_ext() for the bug. The labels should be named after what they do, not after the error path that jumps to them. This way, it is obviously wrong that two labels pointing to the same code mean something is wrong, and checking the code correctness at the goto site is also easier ] ## Which versions are affected by CVE-2024-53044? It affects 1 product. Products: Linux kernel. ## How do I fix CVE-2024-53044? Apply the vendor's patch. ## Is CVE-2024-53044 being exploited? There is no known exploitation of CVE-2024-53044 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-2024-53044 and fix it if it is affected. What it is: CVE-2024-53044 is a high-severity denial of service vulnerability in Linux kernel, published on 19 Nov 2024. 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-2024-53044 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-2024-53044/ (Markdown: https://insights.sbomify.com/CVE-2024-53044/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2024-53044 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-53044 - OSV: https://osv.dev/vulnerability/CVE-2024-53044 --- From sbomify Insights: https://insights.sbomify.com/CVE-2024-53044/ Summaries are generated and may contain mistakes; the official description above is the record.