{"answers":{"affected":"It affects 1 product.","exploited":"There is no known exploitation of CVE-2021-47094 in the wild and no public exploit code.","fix":"Apply the vendor's patch.","what":"CVE-2021-47094 is a high-severity use after free vulnerability in Linux kernel, published on 4 Mar 2024. 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-2021-47094 and fix it if it is affected.\n\nWhat it is: CVE-2021-47094 is a high-severity use after free vulnerability in Linux kernel, published on 4 Mar 2024. 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-2021-47094 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-2021-47094/ (Markdown: https://insights.sbomify.com/CVE-2021-47094/index.md)","id":"CVE-2021-47094","markdown":"https://insights.sbomify.com/CVE-2021-47094/index.md","name":"CVE-2021-47094","record":{"aliases":["DEBIAN-CVE-2021-47094","GHSA-56c7-fm3g-6g6m","UBUNTU-CVE-2021-47094"],"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 flaw in the Linux kernel KVM TDP MMU iterator logic can lead to use-after-free conditions, potentially causing system crashes or arbitrary code execution.","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":[],"description":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Don't advance iterator after restart due to yielding\n\nAfter dropping mmu_lock in the TDP MMU, restart the iterator during\ntdp_iter_next() and do not advance the iterator.  Advancing the iterator\nresults in skipping the top-level SPTE and all its children, which is\nfatal if any of the skipped SPTEs were not visited before yielding.\n\nWhen zapping all SPTEs, i.e. when min_level == root_level, restarting the\niter and then invoking tdp_iter_next() is always fatal if the current gfn\nhas as a valid SPTE, as advancing the iterator results in try_step_side()\nskipping the current gfn, which wasn't visited before yielding.\n\nSprinkle WARNs on iter-\u003eyielded being true in various helpers that are\noften used in conjunction with yielding, and tag the helper with\n__must_check to reduce the probabily of improper usage.\n\nFailing to zap a top-level SPTE manifests in one of two ways.  If a valid\nSPTE is skipped by both kvm_tdp_mmu_zap_all() and kvm_tdp_mmu_put_root(),\nthe shadow page will be leaked and KVM will WARN accordingly.\n\n  WARNING: CPU: 1 PID: 3509 at arch/x86/kvm/mmu/tdp_mmu.c:46 [kvm]\n  RIP: 0010:kvm_mmu_uninit_tdp_mmu+0x3e/0x50 [kvm]\n  Call Trace:\n   \u003cTASK\u003e\n   kvm_arch_destroy_vm+0x130/0x1b0 [kvm]\n   kvm_destroy_vm+0x162/0x2a0 [kvm]\n   kvm_vcpu_release+0x34/0x60 [kvm]\n   __fput+0x82/0x240\n   task_work_run+0x5c/0x90\n   do_exit+0x364/0xa10\n   ? futex_unqueue+0x38/0x60\n   do_group_exit+0x33/0xa0\n   get_signal+0x155/0x850\n   arch_do_signal_or_restart+0xed/0x750\n   exit_to_user_mode_prepare+0xc5/0x120\n   syscall_exit_to_user_mode+0x1d/0x40\n   do_syscall_64+0x48/0xc0\n   entry_SYSCALL_64_after_hwframe+0x44/0xae\n\nIf kvm_tdp_mmu_zap_all() skips a gfn/SPTE but that SPTE is then zapped by\nkvm_tdp_mmu_put_root(), KVM triggers a use-after-free in the form of\nmarking a struct page as dirty/accessed after it has been put back on the\nfree list.  This directly triggers a WARN due to encountering a page with\npage_count() == 0, but it can also lead to data corruption and additional\nerrors in the kernel.\n\n  WARNING: CPU: 7 PID: 1995658 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:171\n  RIP: 0010:kvm_is_zone_device_pfn.part.0+0x9e/0xd0 [kvm]\n  Call Trace:\n   \u003cTASK\u003e\n   kvm_set_pfn_dirty+0x120/0x1d0 [kvm]\n   __handle_changed_spte+0x92e/0xca0 [kvm]\n   __handle_changed_spte+0x63c/0xca0 [kvm]\n   __handle_changed_spte+0x63c/0xca0 [kvm]\n   __handle_changed_spte+0x63c/0xca0 [kvm]\n   zap_gfn_range+0x549/0x620 [kvm]\n   kvm_tdp_mmu_put_root+0x1b6/0x270 [kvm]\n   mmu_free_root_page+0x219/0x2c0 [kvm]\n   kvm_mmu_free_roots+0x1b4/0x4e0 [kvm]\n   kvm_mmu_unload+0x1c/0xa0 [kvm]\n   kvm_arch_destroy_vm+0x1f2/0x5c0 [kvm]\n   kvm_put_kvm+0x3b1/0x8b0 [kvm]\n   kvm_vcpu_release+0x4e/0x70 [kvm]\n   __fput+0x1f7/0x8c0\n   task_work_run+0xf8/0x1a0\n   do_exit+0x97b/0x2230\n   do_group_exit+0xda/0x2a0\n   get_signal+0x3be/0x1e50\n   arch_do_signal_or_restart+0x244/0x17f0\n   exit_to_user_mode_prepare+0xcb/0x120\n   syscall_exit_to_user_mode+0x1d/0x40\n   do_syscall_64+0x4d/0x90\n   entry_SYSCALL_64_after_hwframe+0x44/0xae\n\nNote, the underlying bug existed even before commit 1af4a96025b3 (\"KVM:\nx86/mmu: Yield in TDU MMU iter even if no SPTES changed\") moved calls to\ntdp_mmu_iter_cond_resched() to the beginning of loops, as KVM could still\nincorrectly advance past a top-level entry when yielding on a lower-level\nentry.  But with respect to leaking shadow pages, the bug was introduced\nby yielding before processing the current gfn.\n\nAlternatively, tdp_mmu_iter_cond_resched() could simply fall through, or\ncallers could jump to their \"retry\" label.  The downside of that approach\nis that tdp_mmu_iter_cond_resched() _must_ be called before anything else\nin the loop, and there's no easy way to enfornce that requirement.\n\nIdeally, KVM would handling the cond_resched() fully within the iterator\nmacro (the code is actually quite clean) and avoid this entire class of\nbugs, but that is extremely difficult do wh\n---truncated---","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: Don't advance iterator after restart due to yielding","id":"CVE-2021-47094","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":2,"next":{"headline":"ipmi: ssif: initialize ssif_info-\u003eclient early","id":"CVE-2021-47095"},"packages":[],"prev":{"headline":"platform/x86: intel_pmc_core: fix memleak on registration failure","id":"CVE-2021-47093"},"products":["Linux"],"published":"2024-03-04","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":"FIRST CVSS licence","name":"CVSS (FIRST)"}],"ssvc":{"automatable":"no","exploitation":"none","technical_impact":"partial"},"state":"PUBLISHED","updated":"2026-08-05","vendors":["Linux"]},"summary":"A flaw in the Linux kernel KVM TDP MMU iterator logic can lead to use-after-free conditions, potentially causing system crashes or arbitrary code execution.","url":"https://insights.sbomify.com/CVE-2021-47094/"}