# CVE-2021-47371: nexthop: Fix memory leaks in nexthop notification chain listeners > A memory leak in the Linux kernel nexthop notification chain allows local attackers to cause resource exhaustion and denial of service. - **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/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:** 21 May 2024 - **Updated:** 11 May 2026 - **Also known as:** DEBIAN-CVE-2021-47371, GHSA-8v6f-ww2f-hcqw, UBUNTU-CVE-2021-47371 ## What is CVE-2021-47371? CVE-2021-47371 is a high-severity memory corruption 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: nexthop: Fix memory leaks in nexthop notification chain listeners syzkaller discovered memory leaks [1] that can be reduced to the following commands: # ip nexthop add id 1 blackhole # devlink dev reload pci/0000:06:00.0 As part of the reload flow, mlxsw will unregister its netdevs and then unregister from the nexthop notification chain. Before unregistering from the notification chain, mlxsw will receive delete notifications for nexthop objects using netdevs registered by mlxsw or their uppers. mlxsw will not receive notifications for nexthops using netdevs that are not dismantled as part of the reload flow. For example, the blackhole nexthop above that internally uses the loopback netdev as its nexthop device. One way to fix this problem is to have listeners flush their nexthop tables after unregistering from the notification chain. This is error-prone as evident by this patch and also not symmetric with the registration path where a listener receives a dump of all the existing nexthops. Therefore, fix this problem by replaying delete notifications for the listener being unregistered. This is symmetric to the registration path and also consistent with the netdev notification chain. The above means that unregister_nexthop_notifier(), like register_nexthop_notifier(), will have to take RTNL in order to iterate over the existing nexthops and that any callers of the function cannot hold RTNL. This is true for mlxsw and netdevsim, but not for the VXLAN driver. To avoid a deadlock, change the latter to unregister its nexthop listener without holding RTNL, making it symmetric to the registration path. [1] unreferenced object 0xffff88806173d600 (size 512): comm "syz-executor.0", pid 1290, jiffies 4295583142 (age 143.507s) hex dump (first 32 bytes): 41 9d 1e 60 80 88 ff ff 08 d6 73 61 80 88 ff ff A..`......sa.... 08 d6 73 61 80 88 ff ff 01 00 00 00 00 00 00 00 ..sa............ backtrace: [] kmemleak_alloc_recursive include/linux/kmemleak.h:43 [inline] [] slab_post_alloc_hook+0x96/0x490 mm/slab.h:522 [] slab_alloc_node mm/slub.c:3206 [inline] [] slab_alloc mm/slub.c:3214 [inline] [] kmem_cache_alloc_trace+0x163/0x370 mm/slub.c:3231 [] kmalloc include/linux/slab.h:591 [inline] [] kzalloc include/linux/slab.h:721 [inline] [] mlxsw_sp_nexthop_obj_group_create drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:4918 [inline] [] mlxsw_sp_nexthop_obj_new drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:5054 [inline] [] mlxsw_sp_nexthop_obj_event+0x59a/0x2910 drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:5239 [] notifier_call_chain+0xbd/0x210 kernel/notifier.c:83 [] blocking_notifier_call_chain kernel/notifier.c:318 [inline] [] blocking_notifier_call_chain+0x72/0xa0 kernel/notifier.c:306 [] call_nexthop_notifiers+0x156/0x310 net/ipv4/nexthop.c:244 [] insert_nexthop net/ipv4/nexthop.c:2336 [inline] [] nexthop_add net/ipv4/nexthop.c:2644 [inline] [] rtm_new_nexthop+0x14e8/0x4d10 net/ipv4/nexthop.c:2913 [] rtnetlink_rcv_msg+0x448/0xbf0 net/core/rtnetlink.c:5572 [] netlink_rcv_skb+0x173/0x480 net/netlink/af_netlink.c:2504 [] rtnetlink_rcv+0x22/0x30 net/core/rtnetlink.c:5590 [] netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline] [] netlink_unicast+0x5ae/0x7f0 net/netlink/af_netlink.c:1340 [] netlink_sendmsg+0x8e1/0xe30 net/netlink/af_netlink.c:1929 [] sock_sendmsg_nosec net/socket.c:704 [inline ---truncated--- Weakness: CWE-400 (Uncontrolled Resource Consumption) ## Which versions are affected by CVE-2021-47371? It affects 1 product. Products: Linux kernel. ## How do I fix CVE-2021-47371? Apply the vendor's patch. ## Is CVE-2021-47371 being exploited? There is no known exploitation of CVE-2021-47371 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-2021-47371 and fix it if it is affected. What it is: CVE-2021-47371 is a high-severity memory corruption 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-2021-47371 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-2021-47371/ (Markdown: https://insights.sbomify.com/CVE-2021-47371/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47371 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47371 - OSV: https://osv.dev/vulnerability/CVE-2021-47371 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-47371/ Summaries are generated and may contain mistakes; the official description above is the record.