{ "schemaVersion": 1, "attribution": [ { "source": "CISA Known Exploited Vulnerabilities", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog", "licence": "US government work" }, { "source": "GitHub Advisory Database", "url": "https://github.com/advisories", "licence": "CC BY 4.0" }, { "source": "Have I Been Pwned", "url": "https://haveibeenpwned.com/", "licence": "CC BY 4.0" }, { "source": "CVE Program (CVE records)", "url": "https://www.cve.org/Legal/TermsOfUse", "licence": "CVE Terms of Use", "notice": "Copyright © 1999-2026, The MITRE Corporation. CVE is a trademark and the CVE logo is a registered trademark of The MITRE Corporation.", "terms": "CVE Usage: MITRE hereby grants you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Common Vulnerabilities and Exposures (CVE™). Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy." }, { "source": "FIRST EPSS", "url": "https://www.first.org/epss/", "licence": "free to use; FIRST requests attribution" } ], "record": { "id": "CVE-2026-63806", "sourceURL": "https://www.cve.org/CVERecord?id=CVE-2026-63806", "idYear": 2026, "status": "PUBLISHED", "publishedAt": "2026-07-19T12:02:10.209Z", "updatedAt": "2026-10-19T20:07:48.133Z", "importedAt": "2026-10-24T01:58:20.586Z", "snapshot": { "id": "cve_2026-10-24_midnight_baseline", "at": "2026-10-24T00:00:00.000Z", "source": "https://github.com/CVEProject/cvelistV5/releases/tag/cve_2026-10-24_0100Z" }, "facts": { "title": "KVM: Replace guest-triggerable BUG_ON() in ioeventfd datamatch with get_unaligned()", "summary": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: Replace guest-triggerable BUG_ON() in ioeventfd datamatch with get_unaligned()\n\nDrop a BUG_ON() that has been reachable since it was first added, way back\nin 2009, and instead use get_unaligned() to perform potentially-unaligned\naccesses.\n\nFor a given store, KVM x86's emulator tracks the entire value in the\ndestination operand, x86_emulate_ctxt.dst. If the destination is memory,\nand the target splits multiple pages and/or is emulated MMIO, then KVM\nhandles each fragment independently. E.g. on a page split starting at page\noffset 0xffc, KVM writes 4 bytes to the first page, then the remaining\nbytes to the second page, using ctxt->dst as the source for both (with\nappropriate offsets).\n\nIf the destination splits a page *and* hits emulated MMIO on the second\npage, then KVM will complete the write to the first page, then emulate the\nMMIO access to the second page. If there is a datamatch-enabled ioeventfd\nat offset 0 of the second page, then KVM will process the remainder of the\nstore as a potential ioeventfd signal.\n\nPutting it all together, if the guest emits a store that splits a page\nstarting at page offset N, and the second page has a datamatch-enabled\nioeventfd at offset 0, then KVM will check for datamatch using\n&dst.valptr[N] as the source. Due to dst (and thus dst.valptr) being\n32-byte aligned, if N is not aligned to @len, the BUG_ON() fires.\n\nE.g. with a 16-byte store at page offset 0xffc, to an ioeventfd of len 8,\nall initial checks in ioeventfd_in_range() will succeed, and the BUG_ON()\nfires due to @val being 4-byte aligned, but not 8-byte aligned.\n\n ------------[ cut here ]------------\n kernel BUG at arch/x86/kvm/../../../virt/kvm/eventfd.c:783!\n Oops: invalid opcode: 0000 [#1] SMP\n CPU: 0 UID: 1000 PID: 615 Comm: repro Not tainted 7.1.0-rc2-ff238429d1ea #365 PREEMPT\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n RIP: 0010:ioeventfd_write+0x6c/0x70 [kvm]\n Call Trace:\n \n __kvm_io_bus_write+0x85/0xb0 [kvm]\n kvm_io_bus_write+0x53/0x80 [kvm]\n vcpu_mmio_write+0x66/0xf0 [kvm]\n emulator_read_write_onepage+0x12a/0x540 [kvm]\n emulator_read_write+0x109/0x2b0 [kvm]\n x86_emulate_insn+0x4f8/0xfb0 [kvm]\n x86_emulate_instruction+0x181/0x790 [kvm]\n kvm_mmu_page_fault+0x313/0x630 [kvm]\n vmx_handle_exit+0x18a/0x590 [kvm_intel]\n kvm_arch_vcpu_ioctl_run+0xc81/0x1c90 [kvm]\n kvm_vcpu_ioctl+0x2d5/0x970 [kvm]\n __x64_sys_ioctl+0x8a/0xd0\n do_syscall_64+0xb7/0x890\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\n RIP: 0033:0x7f19c931a9bf\n \n Modules linked in: kvm_intel kvm irqbypass\n ---[ end trace 0000000000000000 ]---\n\nIn a perfect world, the fix would be to simply delete the BUG_ON(), as KVM\nx86 doesn't perform alignment checks on \"normal\" memory accesses at CPL0.\nSadly, C99 ruins all the fun; while the x86 architecture plays nice,\ndereferencing an unaligned pointer directly is undefined behavior in C,\ne.g. triggers splats when running with CONFIG_UBSAN_ALIGNMENT=y.", "affected": [ { "vendor": "Linux", "product": "Linux", "defaultStatus": "unaffected", "versions": [ { "version": "d34e6b175e61821026893ec5298cc8e7558df43a", "status": "affected", "versionType": "git", "lessThan": "2426c15c1395b7d5ccf1e5025ca898af7f3decb6" }, { "version": "d34e6b175e61821026893ec5298cc8e7558df43a", "status": "affected", "versionType": "git", "lessThan": "4186c850789906b875a1d263377a4d37c078e317" }, { "version": "d34e6b175e61821026893ec5298cc8e7558df43a", "status": "affected", "versionType": "git", "lessThan": "36ff44fb3d89960391e013fb9d91e23dbc48be47" }, { "version": "d34e6b175e61821026893ec5298cc8e7558df43a", "status": "affected", "versionType": "git", "lessThan": "92fc631b69deb1c7d56aec2663003600799dcd75" }, { "version": "d34e6b175e61821026893ec5298cc8e7558df43a", "status": "affected", "versionType": "git", "lessThan": "bf89e3738480d33cd515b4a18900e8443d40cd2e" }, { "version": "d34e6b175e61821026893ec5298cc8e7558df43a", "status": "affected", "versionType": "git", "lessThan": "5da9b1a87ec7cc3489c27016313524769f12d9e0" }, { "version": "d34e6b175e61821026893ec5298cc8e7558df43a", "status": "affected", "versionType": "git", "lessThan": "5c87b47374682f69686068ad0a7779365a527b1c" }, { "version": "d34e6b175e61821026893ec5298cc8e7558df43a", "status": "affected", "versionType": "git", "lessThan": "f1edbed787ba67988ed34e0132ca128b052b6ce8" } ] }, { "vendor": "Linux", "product": "Linux", "defaultStatus": "affected", "versions": [ { "version": "2.6.32", "status": "affected" }, { "version": "0", "status": "unaffected", "versionType": "semver", "lessThan": "2.6.32" }, { "version": "5.10.261", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.10.*" }, { "version": "5.15.212", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.15.*" }, { "version": "6.1.178", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.1.*" }, { "version": "6.6.145", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.6.*" }, { "version": "6.12.95", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.12.*" }, { "version": "6.18.38", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.18.*" }, { "version": "7.1.3", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "7.1.*" }, { "version": "7.2", "status": "unaffected", "versionType": "original_commit_for_fix", "lessThanOrEqual": "*" } ] } ] } } }