{"answers":{"affected":"It affects 1 product.","exploited":"There is no known exploitation of CVE-2021-4440 in the wild and no public exploit code.","fix":"Apply the vendor's patch.","what":"CVE-2021-4440 is a high-severity denial of service vulnerability in Linux kernel, published on 25 Jun 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-2021-4440 and fix it if it is affected.\n\nWhat it is: CVE-2021-4440 is a high-severity denial of service vulnerability in Linux kernel, published on 25 Jun 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-2021-4440 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-2021-4440/ (Markdown: https://insights.sbomify.com/CVE-2021-4440/index.md)","id":"CVE-2021-4440","markdown":"https://insights.sbomify.com/CVE-2021-4440/index.md","name":"CVE-2021-4440","record":{"aliases":["DEBIAN-CVE-2021-4440","GHSA-vc52-cgfp-jw27","UBUNTU-CVE-2021-4440"],"analysis":{"component_type":"kernel","fix_type":"patch","impacts":["denial_of_service"],"network_reachable":"adjacent_or_local","non_default_config":true,"product_category":"Linux kernel","requires_auth":"low_privilege","summary":"A missing CPU buffer clearing in Xen PV guests can lead to denial of service or information leakage, requiring kernel patching.","user_interaction":"not_required","vuln_class":"denial_of_service"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"Linux","cpe":[{"product":"linux_kernel","vendor":"linux"}],"cvss":{"score":8.8,"severity":"high","source":"cisa-adp","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H","version":"3.1"},"cwes":[{"id":"CWE-400","name":"Uncontrolled Resource Consumption"}],"description":"In the Linux kernel, the following vulnerability has been resolved:\n\nx86/xen: Drop USERGS_SYSRET64 paravirt call\n\ncommit afd30525a659ac0ae0904f0cb4a2ca75522c3123 upstream.\n\nUSERGS_SYSRET64 is used to return from a syscall via SYSRET, but\na Xen PV guest will nevertheless use the IRET hypercall, as there\nis no sysret PV hypercall defined.\n\nSo instead of testing all the prerequisites for doing a sysret and\nthen mangling the stack for Xen PV again for doing an iret just use\nthe iret exit from the beginning.\n\nThis can easily be done via an ALTERNATIVE like it is done for the\nsysenter compat case already.\n\nIt should be noted that this drops the optimization in Xen for not\nrestoring a few registers when returning to user mode, but it seems\nas if the saved instructions in the kernel more than compensate for\nthis drop (a kernel build in a Xen PV guest was slightly faster with\nthis patch applied).\n\nWhile at it remove the stale sysret32 remnants.\n\n  [ pawan: Brad Spengler and Salvatore Bonaccorso \u003ccarnil@debian.org\u003e\n\t   reported a problem with the 5.10 backport commit edc702b4a820\n\t   (\"x86/entry_64: Add VERW just before userspace transition\").\n\n\t   When CONFIG_PARAVIRT_XXL=y, CLEAR_CPU_BUFFERS is not executed in\n\t   syscall_return_via_sysret path as USERGS_SYSRET64 is runtime\n\t   patched to:\n\n\t.cpu_usergs_sysret64    = { 0x0f, 0x01, 0xf8,\n\t\t\t\t    0x48, 0x0f, 0x07 }, // swapgs; sysretq\n\n\t   which is missing CLEAR_CPU_BUFFERS. It turns out dropping\n\t   USERGS_SYSRET64 simplifies the code, allowing CLEAR_CPU_BUFFERS\n\t   to be explicitly added to syscall_return_via_sysret path. Below\n\t   is with CONFIG_PARAVIRT_XXL=y and this patch applied:\n\n\t   syscall_return_via_sysret:\n\t   ...\n\t   \u003c+342\u003e:   swapgs\n\t   \u003c+345\u003e:   xchg   %ax,%ax\n\t   \u003c+347\u003e:   verw   -0x1a2(%rip)  \u003c------\n\t   \u003c+354\u003e:   sysretq\n  ]","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":"x86/xen: Drop USERGS_SYSRET64 paravirt call","id":"CVE-2021-4440","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":null,"product":"linux:linux_kernel","products":["linux:linux_kernel"],"type":"denial_of_service","year":"2021"},"n_packages":0,"n_references":2,"next":{"headline":"spi: spi-zynq-qspi: Fix a NULL pointer dereference in zynq_qspi_exec_mem_op()","id":"CVE-2021-4441"},"packages":[],"prev":{"headline":"isdn: cpai: check ctr-\u003ecnr to avoid array index out of bound","id":"CVE-2021-4439"},"products":["Linux"],"published":"2024-06-25","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":"2026-05-11","vendors":["Linux"]},"summary":"A missing CPU buffer clearing in Xen PV guests can lead to denial of service or information leakage, requiring kernel patching.","url":"https://insights.sbomify.com/CVE-2021-4440/"}