{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:12",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.1.180-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:13",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.12.95-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.1.3-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "In the Linux kernel, the following vulnerability has been resolved:  KVM: Replace guest-triggerable BUG_ON() in ioeventfd datamatch with get_unaligned()  Drop a BUG_ON() that has been reachable since it was first added, way back in 2009, and instead use get_unaligned() to perform potentially-unaligned accesses.  For a given store, KVM x86's emulator tracks the entire value in the destination operand, x86_emulate_ctxt.dst.  If the destination is memory, and the target splits multiple pages and/or is emulated MMIO, then KVM handles each fragment independently.  E.g. on a page split starting at page offset 0xffc, KVM writes 4 bytes to the first page, then the remaining bytes to the second page, using ctxt-\u003edst as the source for both (with appropriate offsets).  If the destination splits a page *and* hits emulated MMIO on the second page, then KVM will complete the write to the first page, then emulate the MMIO access to the second page.  If there is a datamatch-enabled ioeventfd at offset 0 of the second page, then KVM will process the remainder of the store as a potential ioeventfd signal.  Putting it all together, if the guest emits a store that splits a page starting at page offset N, and the second page has a datamatch-enabled ioeventfd at offset 0, then KVM will check for datamatch using \u0026dst.valptr[N] as the source.  Due to dst (and thus dst.valptr) being 32-byte aligned, if N is not aligned to @len, the BUG_ON() fires.  E.g. with a 16-byte store at page offset 0xffc, to an ioeventfd of len 8, all initial checks in ioeventfd_in_range() will succeed, and the BUG_ON() fires due to @val being 4-byte aligned, but not 8-byte aligned.    ------------[ cut here ]------------   kernel BUG at arch/x86/kvm/../../../virt/kvm/eventfd.c:783!   Oops: invalid opcode: 0000 [#1] SMP   CPU: 0 UID: 1000 PID: 615 Comm: repro Not tainted 7.1.0-rc2-ff238429d1ea #365 PREEMPT   Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015   RIP: 0010:ioeventfd_write+0x6c/0x70 [kvm]   Call Trace:    \u003cTASK\u003e    __kvm_io_bus_write+0x85/0xb0 [kvm]    kvm_io_bus_write+0x53/0x80 [kvm]    vcpu_mmio_write+0x66/0xf0 [kvm]    emulator_read_write_onepage+0x12a/0x540 [kvm]    emulator_read_write+0x109/0x2b0 [kvm]    x86_emulate_insn+0x4f8/0xfb0 [kvm]    x86_emulate_instruction+0x181/0x790 [kvm]    kvm_mmu_page_fault+0x313/0x630 [kvm]    vmx_handle_exit+0x18a/0x590 [kvm_intel]    kvm_arch_vcpu_ioctl_run+0xc81/0x1c90 [kvm]    kvm_vcpu_ioctl+0x2d5/0x970 [kvm]    __x64_sys_ioctl+0x8a/0xd0    do_syscall_64+0xb7/0x890    entry_SYSCALL_64_after_hwframe+0x4b/0x53   RIP: 0033:0x7f19c931a9bf    \u003c/TASK\u003e   Modules linked in: kvm_intel kvm irqbypass   ---[ end trace 0000000000000000 ]---  In a perfect world, the fix would be to simply delete the BUG_ON(), as KVM x86 doesn't perform alignment checks on \"normal\" memory accesses at CPL0. Sadly, C99 ruins all the fun; while the x86 architecture plays nice, dereferencing an unaligned pointer directly is undefined behavior in C, e.g. triggers splats when running with CONFIG_UBSAN_ALIGNMENT=y.",
  "id": "DEBIAN-CVE-2026-63806",
  "modified": "2026-09-14T16:47:39.618057117Z",
  "published": "2026-07-19T12:16:53.340Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-63806"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "upstream": [
    "CVE-2026-63806"
  ]
}