{"answers":{"affected":"It affects 1 product.","exploited":"There is no known exploitation of CVE-2021-47639 in the wild and no public exploit code.","fix":"Apply the vendor's patch.","what":"CVE-2021-47639 is a high-severity use after free vulnerability in Linux kernel, published on 26 Feb 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-2021-47639 and fix it if it is affected.\n\nWhat it is: CVE-2021-47639 is a high-severity use after free vulnerability in Linux kernel, published on 26 Feb 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-2021-47639 in the wild and no public exploit code.\n\nAffected product: Linux kernel. 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-2021-47639/ (Markdown: https://insights.sbomify.com/CVE-2021-47639/index.md)","id":"CVE-2021-47639","markdown":"https://insights.sbomify.com/CVE-2021-47639/index.md","name":"CVE-2021-47639","record":{"aliases":["DEBIAN-CVE-2021-47639","GHSA-7fq4-85x5-74rc","UBUNTU-CVE-2021-47639"],"analysis":{"component_type":"kernel","fix_type":"patch","impacts":["denial_of_service","code_execution"],"network_reachable":"adjacent_or_local","non_default_config":false,"product_category":"Linux kernel KVM","requires_auth":"low_privilege","summary":"A use-after-free vulnerability in the Linux kernel's KVM TDP MMU allows attackers to cause a system crash or potentially execute arbitrary code.","user_interaction":"not_required","vuln_class":"use_after_free"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"Linux","cpe":[{"product":"linux_kernel","vendor":"linux"}],"cvss":{"score":7.8,"severity":"high","source":"cna","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"},"cwes":[{"id":"CWE-416","name":"Use After Free"}],"description":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Zap _all_ roots when unmapping gfn range in TDP MMU\n\nZap both valid and invalid roots when zapping/unmapping a gfn range, as\nKVM must ensure it holds no references to the freed page after returning\nfrom the unmap operation.  Most notably, the TDP MMU doesn't zap invalid\nroots in mmu_notifier callbacks.  This leads to use-after-free and other\nissues if the mmu_notifier runs to completion while an invalid root\nzapper yields as KVM fails to honor the requirement that there must be\n_no_ references to the page after the mmu_notifier returns.\n\nThe bug is most easily reproduced by hacking KVM to cause a collision\nbetween set_nx_huge_pages() and kvm_mmu_notifier_release(), but the bug\nexists between kvm_mmu_notifier_invalidate_range_start() and memslot\nupdates as well.  Invalidating a root ensures pages aren't accessible by\nthe guest, and KVM won't read or write page data itself, but KVM will\ntrigger e.g. kvm_set_pfn_dirty() when zapping SPTEs, and thus completing\na zap of an invalid root _after_ the mmu_notifier returns is fatal.\n\n  WARNING: CPU: 24 PID: 1496 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:173 [kvm]\n  RIP: 0010:kvm_is_zone_device_pfn+0x96/0xa0 [kvm]\n  Call Trace:\n   \u003cTASK\u003e\n   kvm_set_pfn_dirty+0xa8/0xe0 [kvm]\n   __handle_changed_spte+0x2ab/0x5e0 [kvm]\n   __handle_changed_spte+0x2ab/0x5e0 [kvm]\n   __handle_changed_spte+0x2ab/0x5e0 [kvm]\n   zap_gfn_range+0x1f3/0x310 [kvm]\n   kvm_tdp_mmu_zap_invalidated_roots+0x50/0x90 [kvm]\n   kvm_mmu_zap_all_fast+0x177/0x1a0 [kvm]\n   set_nx_huge_pages+0xb4/0x190 [kvm]\n   param_attr_store+0x70/0x100\n   module_attr_store+0x19/0x30\n   kernfs_fop_write_iter+0x119/0x1b0\n   new_sync_write+0x11c/0x1b0\n   vfs_write+0x1cc/0x270\n   ksys_write+0x5f/0xe0\n   do_syscall_64+0x38/0xc0\n   entry_SYSCALL_64_after_hwframe+0x44/0xae\n   \u003c/TASK\u003e","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":"KVM: x86/mmu: Zap _all_ roots when unmapping gfn range in TDP MMU","id":"CVE-2021-47639","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":null,"product":"linux:linux_kernel","products":["linux:linux_kernel"],"type":"use_after_free","year":"2021"},"n_packages":0,"n_references":4,"next":{"headline":"powerpc/kasan: Fix early region not updated correctly","id":"CVE-2021-47640"},"packages":[],"prev":{"headline":"ubifs: rename_whiteout: Fix double free for whiteout_ui-\u003edata","id":"CVE-2021-47638"},"products":["Linux"],"published":"2025-02-26","related":[{"cvss_score":8.8,"headline":"Linux Kernel Out-of-Bounds Write","id":"CVE-2026-53266","kev_date_added":"2026-09-18","published":"2026-06-25"},{"cvss_score":8.8,"headline":"Linux Kernel Improper Input Validation","id":"CVE-2013-6282","kev_date_added":"2022-09-15","published":"2013-11-19"},{"cvss_score":8.4,"headline":"Linux Kernel Heap-Based Buffer Overflow","id":"CVE-2022-0185","kev_date_added":"2024-08-21","published":"2022-02-11"},{"cvss_score":8.4,"headline":"Linux Kernel Privilege Escalation","id":"CVE-2013-2094","kev_date_added":"2022-09-15","published":"2013-05-14"},{"cvss_score":7.8,"headline":"Linux Kernel Unspecified","id":"CVE-2026-53362","kev_date_added":"2026-08-27","published":"2026-07-04"},{"cvss_score":7.8,"headline":"Linux Kernel Missing Initialization of a Variable","id":"CVE-2026-46300","kev_date_added":"2026-10-28","published":"2026-05-23"},{"cvss_score":7.8,"headline":"Linux Kernel Race Condition","id":"CVE-2025-39964","kev_date_added":"2026-09-18","published":"2025-10-13"}],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"},{"class":"attribution","licence":"US public information, NVD API terms","name":"NVD"},{"class":"attribution","licence":"CWE Terms of Use","name":"CWE (MITRE)"},{"class":"attribution","licence":"FIRST CVSS licence","name":"CVSS (FIRST)"}],"ssvc":{"automatable":"no","exploitation":"none","technical_impact":"total"},"state":"PUBLISHED","updated":"2026-08-05","vendors":["Linux"]},"summary":"A use-after-free vulnerability in the Linux kernel's KVM TDP MMU allows attackers to cause a system crash or potentially execute arbitrary code.","url":"https://insights.sbomify.com/CVE-2021-47639/"}