{"answers":{"affected":"","exploited":"There is no known exploitation of CVE-2025-40220 in the wild and no public exploit code.","fix":"Apply the vendor's patch.","what":"CVE-2025-40220 is a denial of service vulnerability in Linux, published on 4 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim."},"fix_prompt":"Check this codebase for CVE-2025-40220 and fix it if it is affected.\n\nWhat it is: CVE-2025-40220 is a denial of service vulnerability in Linux, published on 4 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.\nExploitation: There is no known exploitation of CVE-2025-40220 in the wild and no public exploit code.\n\nAffected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.\n\nTask:\n1. 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.\n2. 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.\n3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.\n4. Run the tests and summarise what changed and why.\n5. If nothing in the project is affected, say so and change nothing.\n\nReference: https://insights.sbomify.com/CVE-2025-40220/ (Markdown: https://insights.sbomify.com/CVE-2025-40220/index.md)","id":"CVE-2025-40220","markdown":"https://insights.sbomify.com/CVE-2025-40220/index.md","name":"CVE-2025-40220","record":{"aliases":["AZL-71290","BELL-CVE-2025-40220","DEBIAN-CVE-2025-40220","GHSA-f6j8-wgmp-w2x6","ROOT-OS-DEBIAN-11-CVE-2025-40220","ROOT-OS-UBUNTU-2404-CVE-2025-40220","UBUNTU-CVE-2025-40220"],"analysis":{"component_type":"kernel","fix_type":"patch","impacts":["denial_of_service"],"network_reachable":"adjacent_or_local","non_default_config":false,"product_category":"Linux kernel","requires_auth":"none","summary":"A local attacker can cause a system hang in the Linux kernel FUSE module by triggering a livelock during synchronous file operations.","user_interaction":"not_required","vuln_class":"denial_of_service"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"Linux","cpe":[],"cvss":{"score":null,"severity":null,"source":null,"vector":null,"version":null},"cwes":[],"description":"In the Linux kernel, the following vulnerability has been resolved:\n\nfuse: fix livelock in synchronous file put from fuseblk workers\n\nI observed a hang when running generic/323 against a fuseblk server.\nThis test opens a file, initiates a lot of AIO writes to that file\ndescriptor, and closes the file descriptor before the writes complete.\nUnsurprisingly, the AIO exerciser threads are mostly stuck waiting for\nresponses from the fuseblk server:\n\n# cat /proc/372265/task/372313/stack\n[\u003c0\u003e] request_wait_answer+0x1fe/0x2a0 [fuse]\n[\u003c0\u003e] __fuse_simple_request+0xd3/0x2b0 [fuse]\n[\u003c0\u003e] fuse_do_getattr+0xfc/0x1f0 [fuse]\n[\u003c0\u003e] fuse_file_read_iter+0xbe/0x1c0 [fuse]\n[\u003c0\u003e] aio_read+0x130/0x1e0\n[\u003c0\u003e] io_submit_one+0x542/0x860\n[\u003c0\u003e] __x64_sys_io_submit+0x98/0x1a0\n[\u003c0\u003e] do_syscall_64+0x37/0xf0\n[\u003c0\u003e] entry_SYSCALL_64_after_hwframe+0x4b/0x53\n\nBut the /weird/ part is that the fuseblk server threads are waiting for\nresponses from itself:\n\n# cat /proc/372210/task/372232/stack\n[\u003c0\u003e] request_wait_answer+0x1fe/0x2a0 [fuse]\n[\u003c0\u003e] __fuse_simple_request+0xd3/0x2b0 [fuse]\n[\u003c0\u003e] fuse_file_put+0x9a/0xd0 [fuse]\n[\u003c0\u003e] fuse_release+0x36/0x50 [fuse]\n[\u003c0\u003e] __fput+0xec/0x2b0\n[\u003c0\u003e] task_work_run+0x55/0x90\n[\u003c0\u003e] syscall_exit_to_user_mode+0xe9/0x100\n[\u003c0\u003e] do_syscall_64+0x43/0xf0\n[\u003c0\u003e] entry_SYSCALL_64_after_hwframe+0x4b/0x53\n\nThe fuseblk server is fuse2fs so there's nothing all that exciting in\nthe server itself.  So why is the fuse server calling fuse_file_put?\nThe commit message for the fstest sheds some light on that:\n\n\"By closing the file descriptor before calling io_destroy, you pretty\nmuch guarantee that the last put on the ioctx will be done in interrupt\ncontext (during I/O completion).\n\nAha.  AIO fgets a new struct file from the fd when it queues the ioctx.\nThe completion of the FUSE_WRITE command from userspace causes the fuse\nserver to call the AIO completion function.  The completion puts the\nstruct file, queuing a delayed fput to the fuse server task.  When the\nfuse server task returns to userspace, it has to run the delayed fput,\nwhich in the case of a fuseblk server, it does synchronously.\n\nSending the FUSE_RELEASE command sychronously from fuse server threads\nis a bad idea because a client program can initiate enough simultaneous\nAIOs such that all the fuse server threads end up in delayed_fput, and\nnow there aren't any threads left to handle the queued fuse commands.\n\nFix this by only using asynchronous fputs when closing files, and leave\na comment explaining why.","ecosystems":[],"exploits":{"exploitdb":0,"first_seen":null,"github_poc":0,"max_poc_stars":null,"metasploit":0,"nuclei":0,"refs":[],"tier":"none_known"},"has_fix":true,"headline":"fuse: fix livelock in synchronous file put from fuseblk workers","id":"CVE-2025-40220","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":null,"product":null,"products":[],"type":"denial_of_service","year":"2025"},"n_packages":0,"n_references":7,"next":{"headline":"media: pci: mg4b: fix uninitialized iio scan data","id":"CVE-2025-40221"},"packages":[],"prev":{"headline":"PCI/IOV: Fix race between SR-IOV enable/disable and hotplug","id":"CVE-2025-40219"},"products":["Linux"],"published":"2025-12-04","related":[],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"}],"ssvc":{"automatable":null,"exploitation":null,"technical_impact":null},"state":"PUBLISHED","updated":"2026-05-23","vendors":["Linux"]},"summary":"A local attacker can cause a system hang in the Linux kernel FUSE module by triggering a livelock during synchronous file operations.","url":"https://insights.sbomify.com/CVE-2025-40220/"}