CVE-2025-40026 (GCVE-0-2025-40026)

Vulnerability from cvelistv5 – Published: 2025-10-28 09:32 – Updated: 2026-08-05 12:07
VLAI
Title
KVM: x86: Don't (re)check L1 intercepts when completing userspace I/O
Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Don't (re)check L1 intercepts when completing userspace I/O When completing emulation of instruction that generated a userspace exit for I/O, don't recheck L1 intercepts as KVM has already finished that phase of instruction execution, i.e. has already committed to allowing L2 to perform I/O. If L1 (or host userspace) modifies the I/O permission bitmaps during the exit to userspace, KVM will treat the access as being intercepted despite already having emulated the I/O access. Pivot on EMULTYPE_NO_DECODE to detect that KVM is completing emulation. Of the three users of EMULTYPE_NO_DECODE, only complete_emulated_io() (the intended "recipient") can reach the code in question. gp_interception()'s use is mutually exclusive with is_guest_mode(), and complete_emulated_insn_gp() unconditionally pairs EMULTYPE_NO_DECODE with EMULTYPE_SKIP. The bad behavior was detected by a syzkaller program that toggles port I/O interception during the userspace I/O exit, ultimately resulting in a WARN on vcpu->arch.pio.count being non-zero due to KVM no completing emulation of the I/O instruction. WARNING: CPU: 23 PID: 1083 at arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm] Modules linked in: kvm_intel kvm irqbypass CPU: 23 UID: 1000 PID: 1083 Comm: repro Not tainted 6.16.0-rc5-c1610d2d66b1-next-vm #74 NONE Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm] PKRU: 55555554 Call Trace: <TASK> kvm_fast_pio+0xd6/0x1d0 [kvm] vmx_handle_exit+0x149/0x610 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm] kvm_vcpu_ioctl+0x244/0x8c0 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0x5d/0xc60 entry_SYSCALL_64_after_hwframe+0x4b/0x53 </TASK>
Severity
7.9 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 , < a908eca437789589dd4624da428614c1275064dc (git)
Affected: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 , < 00338255bb1f422642fb2798ebe92e93b6e4209b (git)
Affected: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 , < e0ce3ed1048a47986d15aef1a98ebda25560d257 (git)
Affected: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 , < ba35a5d775799ce5ad60230be97336f2fefd518e (git)
Affected: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 , < 3d3abf3f7e8b1abb082070a343de82d7efc80523 (git)
Affected: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 , < e7177c7e32cb806f348387b7f4faafd4a5b32054 (git)
Affected: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 , < 3a062a5c55adc5507600b9ae6d911e247e2f1d6e (git)
Affected: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 , < 7366830642505683bbe905a2ba5d18d6e4b512b8 (git)
Affected: 8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 , < e750f85391286a4c8100275516973324b621a269 (git)
Create a notification for this product.
Linux Linux Affected: 3.0
Unaffected: 0 , < 3.0 (semver)
Unaffected: 5.4.301 , ≤ 5.4.* (semver)
Unaffected: 5.10.246 , ≤ 5.10.* (semver)
Unaffected: 5.15.195 , ≤ 5.15.* (semver)
Unaffected: 6.1.157 , ≤ 6.1.* (semver)
Unaffected: 6.6.111 , ≤ 6.6.* (semver)
Unaffected: 6.12.52 , ≤ 6.12.* (semver)
Unaffected: 6.16.12 , ≤ 6.16.* (semver)
Unaffected: 6.17.2 , ≤ 6.17.* (semver)
Unaffected: 6.18 , ≤ * (original_commit_for_fix)
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{
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86: Don\u0027t (re)check L1 intercepts when completing userspace I/O\n\nWhen completing emulation of instruction that generated a userspace exit\nfor I/O, don\u0027t recheck L1 intercepts as KVM has already finished that\nphase of instruction execution, i.e. has already committed to allowing L2\nto perform I/O.  If L1 (or host userspace) modifies the I/O permission\nbitmaps during the exit to userspace,  KVM will treat the access as being\nintercepted despite already having emulated the I/O access.\n\nPivot on EMULTYPE_NO_DECODE to detect that KVM is completing emulation.\nOf the three users of EMULTYPE_NO_DECODE, only complete_emulated_io() (the\nintended \"recipient\") can reach the code in question.  gp_interception()\u0027s\nuse is mutually exclusive with is_guest_mode(), and\ncomplete_emulated_insn_gp() unconditionally pairs EMULTYPE_NO_DECODE with\nEMULTYPE_SKIP.\n\nThe bad behavior was detected by a syzkaller program that toggles port I/O\ninterception during the userspace I/O exit, ultimately resulting in a WARN\non vcpu-\u003earch.pio.count being non-zero due to KVM no completing emulation\nof the I/O instruction.\n\n  WARNING: CPU: 23 PID: 1083 at arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm]\n  Modules linked in: kvm_intel kvm irqbypass\n  CPU: 23 UID: 1000 PID: 1083 Comm: repro Not tainted 6.16.0-rc5-c1610d2d66b1-next-vm #74 NONE\n  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n  RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm]\n  PKRU: 55555554\n  Call Trace:\n   \u003cTASK\u003e\n   kvm_fast_pio+0xd6/0x1d0 [kvm]\n   vmx_handle_exit+0x149/0x610 [kvm_intel]\n   kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm]\n   kvm_vcpu_ioctl+0x244/0x8c0 [kvm]\n   __x64_sys_ioctl+0x8a/0xd0\n   do_syscall_64+0x5d/0xc60\n   entry_SYSCALL_64_after_hwframe+0x4b/0x53\n   \u003c/TASK\u003e"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.9,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - Exploitation requires either `KVM_RUN`/`ioctl()` access to `/dev/kvm` on the host or code execution inside a guest running a nested hypervisor; there is no network-reachable path to `x86_emulate_insn()`.\nAC:L - The syzkaller reproducer deterministically toggles the port-I/O bitmap while servicing the `KVM_EXIT_IO` exit, and the guest-side variant only needs a second L1 vCPU to write the bitmap page \u2014 the attacker controls both sides of the window, and nested virt is enabled by default on kvm_intel/kvm_amd.\nPR:L - The attacker needs only unprivileged access to `/dev/kvm` (commonly granted via the `kvm` group or a VMM process), or ordinary code execution inside a guest; no root or CAP_SYS_ADMIN in the init namespace is required.\nUI:N - The vCPU thread reaches the buggy re-check on the normal `KVM_RUN` re-entry path after a userspace I/O exit; no victim action is needed.\nS:C - A guest (L1/L2) triggers corrupted state and a WARN/panic in the host kernel\u0027s KVM module, crossing the guest-to-host security boundary, and the aborted emulation also crosses the L1/L2 authority boundary by delivering an I/O intercept L1 never legitimately received.\nC:L - The stale `pio.count`/`pio.size` makes the next emulated `in` take the completion path and hand back data captured during the earlier I/O read on L2\u0027s behalf, leaking bounded `pio_data` contents across the L1/L2 boundary; the copy is capped at the 1024-byte `read_cache`, so it is not an arbitrary read.\nI:L - KVM injects a nested IOIO VM-exit to L1 for an access it already performed against the host device model (double execution) and subsequently substitutes stale `pio_data` for a real port read, corrupting guest I/O state in a limited, non-arbitrary way.\nA:H - The un-cleared `vcpu-\u003earch.pio.count` trips `WARN_ON_ONCE()` in `emulator_pio_in_out()` in the host kernel \u2014 a full host panic on the widely deployed `panic_on_warn=1` configuration \u2014 and leaves the vCPU with permanently desynchronized emulation state."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:07:08.793Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/a908eca437789589dd4624da428614c1275064dc"
        },
        {
          "url": "https://git.kernel.org/stable/c/00338255bb1f422642fb2798ebe92e93b6e4209b"
        },
        {
          "url": "https://git.kernel.org/stable/c/e0ce3ed1048a47986d15aef1a98ebda25560d257"
        },
        {
          "url": "https://git.kernel.org/stable/c/ba35a5d775799ce5ad60230be97336f2fefd518e"
        },
        {
          "url": "https://git.kernel.org/stable/c/3d3abf3f7e8b1abb082070a343de82d7efc80523"
        },
        {
          "url": "https://git.kernel.org/stable/c/e7177c7e32cb806f348387b7f4faafd4a5b32054"
        },
        {
          "url": "https://git.kernel.org/stable/c/3a062a5c55adc5507600b9ae6d911e247e2f1d6e"
        },
        {
          "url": "https://git.kernel.org/stable/c/7366830642505683bbe905a2ba5d18d6e4b512b8"
        },
        {
          "url": "https://git.kernel.org/stable/c/e750f85391286a4c8100275516973324b621a269"
        }
      ],
      "title": "KVM: x86: Don\u0027t (re)check L1 intercepts when completing userspace I/O",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-40026",
    "datePublished": "2025-10-28T09:32:33.075Z",
    "dateReserved": "2025-04-16T07:20:57.152Z",
    "dateUpdated": "2026-08-05T12:07:08.793Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2025-40026",
      "date": "2026-08-14",
      "epss": "0.00158",
      "percentile": "0.0551"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2025-40026\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-10-28T10:15:42.167\",\"lastModified\":\"2026-07-30T06:24:06.610\",\"vulnStatus\":\"Deferred\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nKVM: x86: Don\u0027t (re)check L1 intercepts when completing userspace I/O\\n\\nWhen completing emulation of instruction that generated a userspace exit\\nfor I/O, don\u0027t recheck L1 intercepts as KVM has already finished that\\nphase of instruction execution, i.e. has already committed to allowing L2\\nto perform I/O.  If L1 (or host userspace) modifies the I/O permission\\nbitmaps during the exit to userspace,  KVM will treat the access as being\\nintercepted despite already having emulated the I/O access.\\n\\nPivot on EMULTYPE_NO_DECODE to detect that KVM is completing emulation.\\nOf the three users of EMULTYPE_NO_DECODE, only complete_emulated_io() (the\\nintended \\\"recipient\\\") can reach the code in question.  gp_interception()\u0027s\\nuse is mutually exclusive with is_guest_mode(), and\\ncomplete_emulated_insn_gp() unconditionally pairs EMULTYPE_NO_DECODE with\\nEMULTYPE_SKIP.\\n\\nThe bad behavior was detected by a syzkaller program that toggles port I/O\\ninterception during the userspace I/O exit, ultimately resulting in a WARN\\non vcpu-\u003earch.pio.count being non-zero due to KVM no completing emulation\\nof the I/O instruction.\\n\\n  WARNING: CPU: 23 PID: 1083 at arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm]\\n  Modules linked in: kvm_intel kvm irqbypass\\n  CPU: 23 UID: 1000 PID: 1083 Comm: repro Not tainted 6.16.0-rc5-c1610d2d66b1-next-vm #74 NONE\\n  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\\n  RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm]\\n  PKRU: 55555554\\n  Call Trace:\\n   \u003cTASK\u003e\\n   kvm_fast_pio+0xd6/0x1d0 [kvm]\\n   vmx_handle_exit+0x149/0x610 [kvm_intel]\\n   kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm]\\n   kvm_vcpu_ioctl+0x244/0x8c0 [kvm]\\n   __x64_sys_ioctl+0x8a/0xd0\\n   do_syscall_64+0x5d/0xc60\\n   entry_SYSCALL_64_after_hwframe+0x4b/0x53\\n   \u003c/TASK\u003e\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"arch/x86/kvm/emulate.c\",\"arch/x86/kvm/kvm_emulate.h\",\"arch/x86/kvm/x86.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9\",\"lessThan\":\"a908eca437789589dd4624da428614c1275064dc\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9\",\"lessThan\":\"00338255bb1f422642fb2798ebe92e93b6e4209b\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9\",\"lessThan\":\"e0ce3ed1048a47986d15aef1a98ebda25560d257\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9\",\"lessThan\":\"ba35a5d775799ce5ad60230be97336f2fefd518e\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9\",\"lessThan\":\"3d3abf3f7e8b1abb082070a343de82d7efc80523\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9\",\"lessThan\":\"e7177c7e32cb806f348387b7f4faafd4a5b32054\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9\",\"lessThan\":\"3a062a5c55adc5507600b9ae6d911e247e2f1d6e\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9\",\"lessThan\":\"7366830642505683bbe905a2ba5d18d6e4b512b8\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9\",\"lessThan\":\"e750f85391286a4c8100275516973324b621a269\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"arch/x86/kvm/emulate.c\",\"arch/x86/kvm/kvm_emulate.h\",\"arch/x86/kvm/x86.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"3.0\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"3.0\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.4.301\",\"lessThanOrEqual\":\"5.4.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.10.246\",\"lessThanOrEqual\":\"5.10.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.15.195\",\"lessThanOrEqual\":\"5.15.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.1.157\",\"lessThanOrEqual\":\"6.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.6.111\",\"lessThanOrEqual\":\"6.6.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.12.52\",\"lessThanOrEqual\":\"6.12.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.16.12\",\"lessThanOrEqual\":\"6.16.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.17.2\",\"lessThanOrEqual\":\"6.17.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H\",\"baseScore\":7.9,\"baseSeverity\":\"HIGH\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"CHANGED\",\"confidentialityImpact\":\"LOW\",\"integrityImpact\":\"LOW\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":2.0,\"impactScore\":5.3}]},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/00338255bb1f422642fb2798ebe92e93b6e4209b\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/3a062a5c55adc5507600b9ae6d911e247e2f1d6e\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/3d3abf3f7e8b1abb082070a343de82d7efc80523\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/7366830642505683bbe905a2ba5d18d6e4b512b8\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/a908eca437789589dd4624da428614c1275064dc\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/ba35a5d775799ce5ad60230be97336f2fefd518e\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/e0ce3ed1048a47986d15aef1a98ebda25560d257\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/e7177c7e32cb806f348387b7f4faafd4a5b32054\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/e750f85391286a4c8100275516973324b621a269\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-13T17:39:11+00:00",
      "cve": "CVE-2025-40026",
      "id": "CVE-2025-40026",
      "initial_release_date": "2025-10-28T00:00:00+00:00",
      "product_status:fixed": "1571",
      "product_status:known_affected": "127",
      "product_status:known_not_affected": "15",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: KVM: x86: Don\u0027t (re)check L1 intercepts when completing userspace I/O",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-40026.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "low",
      "current_release_date": "2026-07-26T23:33:21Z",
      "cve": "CVE-2025-40026",
      "id": "CVE-2025-40026",
      "initial_release_date": "2025-10-29T00:25:45Z",
      "product_status:known_affected": "242",
      "product_status:recommended": "26",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2025-40026",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2025-40026.json",
      "version": "13"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.