# CVE-2021-47266: RDMA/ipoib: Fix warning caused by destroying non-initial netns > A null pointer dereference in the Linux kernel RDMA/ipoib module causes a system crash when destroying a non-initial network namespace. - **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 21 May 2024 - **Updated:** 23 May 2026 - **Also known as:** DEBIAN-CVE-2021-47266, GHSA-8cxw-6695-4jq3, UBUNTU-CVE-2021-47266 ## What is CVE-2021-47266? CVE-2021-47266 is a medium-severity vulnerability in Linux kernel, published on 21 May 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: RDMA/ipoib: Fix warning caused by destroying non-initial netns After the commit 5ce2dced8e95 ("RDMA/ipoib: Set rtnl_link_ops for ipoib interfaces"), if the IPoIB device is moved to non-initial netns, destroying that netns lets the device vanish instead of moving it back to the initial netns, This is happening because default_device_exit() skips the interfaces due to having rtnl_link_ops set. Steps to reporoduce: ip netns add foo ip link set mlx5_ib0 netns foo ip netns delete foo WARNING: CPU: 1 PID: 704 at net/core/dev.c:11435 netdev_exit+0x3f/0x50 Modules linked in: xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT nf_reject_ipv4 nft_compat nft_counter nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables nfnetlink tun d fuse CPU: 1 PID: 704 Comm: kworker/u64:3 Tainted: G S W 5.13.0-rc1+ #1 Hardware name: Dell Inc. PowerEdge R630/02C2CP, BIOS 2.1.5 04/11/2016 Workqueue: netns cleanup_net RIP: 0010:netdev_exit+0x3f/0x50 Code: 48 8b bb 30 01 00 00 e8 ef 81 b1 ff 48 81 fb c0 3a 54 a1 74 13 48 8b 83 90 00 00 00 48 81 c3 90 00 00 00 48 39 d8 75 02 5b c3 <0f> 0b 5b c3 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 0f 1f 44 00 RSP: 0018:ffffb297079d7e08 EFLAGS: 00010206 RAX: ffff8eb542c00040 RBX: ffff8eb541333150 RCX: 000000008010000d RDX: 000000008010000e RSI: 000000008010000d RDI: ffff8eb440042c00 RBP: ffffb297079d7e48 R08: 0000000000000001 R09: ffffffff9fdeac00 R10: ffff8eb5003be000 R11: 0000000000000001 R12: ffffffffa1545620 R13: ffffffffa1545628 R14: 0000000000000000 R15: ffffffffa1543b20 FS: 0000000000000000(0000) GS:ffff8ed37fa00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00005601b5f4c2e8 CR3: 0000001fc8c10002 CR4: 00000000003706e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: ops_exit_list.isra.9+0x36/0x70 cleanup_net+0x234/0x390 process_one_work+0x1cb/0x360 ? process_one_work+0x360/0x360 worker_thread+0x30/0x370 ? process_one_work+0x360/0x360 kthread+0x116/0x130 ? kthread_park+0x80/0x80 ret_from_fork+0x22/0x30 To avoid the above warning and later on the kernel panic that could happen on shutdown due to a NULL pointer dereference, make sure to set the netns_refund flag that was introduced by commit 3a5ca857079e ("can: dev: Move device back to init netns on owning netns delete") to properly restore the IPoIB interfaces to the initial netns. Weakness: CWE-476 (NULL Pointer Dereference) ## Which versions are affected by CVE-2021-47266? It affects 1 product. Products: Linux kernel. ## How do I fix CVE-2021-47266? Apply the vendor's patch. ## Is CVE-2021-47266 being exploited? There is no known exploitation of CVE-2021-47266 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-2021-47266 and fix it if it is affected. What it is: CVE-2021-47266 is a medium-severity vulnerability in Linux kernel, published on 21 May 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-2021-47266 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-2021-47266/ (Markdown: https://insights.sbomify.com/CVE-2021-47266/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47266 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47266 - OSV: https://osv.dev/vulnerability/CVE-2021-47266 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-47266/ Summaries are generated and may contain mistakes; the official description above is the record.