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CWE-250Weakness · CWE-250

CVE-2026-23559

CRITICAL · 9.4 CVSS v4.0 Published 2026-07-09
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
99/100
Remediation priority · Urgent
No privileges Zero-click 6 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
[This CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] XAPI can configure different users with different roles, using Role Based Access Control. For more details, see: https://docs.xenserver.com/en-us/xencenter/current-release/rbac-overview.html#rbac-roles The pool-admin role is fully privileged. Notably, users with this role can also SSH into the host as root. The other administrator roles are pool-operator, vm-power-admin and vm-admin, each of which are authorised to configure and manage various aspects of the system. Some settings are inadequately restricted, and can be set by a lower privilege of administrator than expected. * CVE-2026-23559: A vm-admin can set VBD.other_config:backend-local and turn arbitrary files in dom0 into VDIs (virtual disks) and give said disks to a VM they control. This is an arbitrary read and/or modify of files in dom0. * CVE-2026-23560: A vm-admin can set VM.other-config:is_system_domain and mark a VM as a system domain. System domains are ignored and left running during certain other host/pool operations, and may be hidden from view in tooling. * CVE-2026-23561: A vm-admin can set VM.other_config:storage_driver_domain and mark a VM as the storage domain for a particular host storage connection (PBD). Shutting down the VM can cause the PBD to be erroneously marked as unplugged when it is not. * CVE-2026-23562: Configuration of PCI passthrough is normally restricted to the pool-admin role. However one API was missing this check, allowing a vm-admin access to unintended host hardware. * CVE-2026-42486: A vm-admin can set the VM.platform:hvm_serial parameter, which should be restricted to the pool-admin role, as it can allow arbitrary dom0 file write.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

In XenServer's XAPI, a vm-admin role user can set VBD.other_config:backend-local to mount arbitrary dom0 files as virtual disks, achieving arbitrary file read and/or modification in the privileged dom0 domain. This is a privilege escalation from vm-admin to full dom0 access.

MitigationRestrict vm-admin role permissions from setting VBD.other_config:backend-local; enforce proper RBAC checks at the API layer; apply vendor patch when available.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
None
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Confirm XenServer XAPI environment
    Run 'xe host-list' or check for /etc/xensource directory and xapi process running via 'ps aux | grep xapi'
    Affected if Running on XenServer with XAPI service present
  2. Identify vm-admin role existence
    Run 'xe role-list' and look for vm-admin role, or check RBAC configuration file /etc/xensource/rbac.data
    Affected if vm-admin role is defined and enabled in the environment
  3. Check VBD other_config for backend-local entries
    Run 'xe vbd-list --all' and inspect other_config fields for 'backend-local' key, or query: xe vbd-param-get param-name=other_config
    Affected if Any VBD objects contain backend-local configuration set to a dom0 file path
  4. Verify RBAC allows vm-admin to modify VBD other_config
    Check RBAC permissions: grep -r 'VBD' /etc/xensource/*.json or examine API role permissions for vm-admin role
    Affected if vm-admin role has permission to modify VBD other_config parameters
  5. Test if vm-admin can set backend-local
    As a vm-admin user, attempt: xe vbd-param-set other_config:backend-local=/etc/passwd uuid=<vbd_uuid>
    Affected if Operation succeeds without permission denied error

A XenServer environment is affected if vm-admin role users can set VBD.other_config:backend-local to point to arbitrary dom0 file paths, enabling privilege escalation to dom0.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Restrict vm-admin role permissions from setting VBD.other_config:backend-local; enforce proper RBAC checks at the API layer; apply vendor patch when available.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA6.0 h
30.0 hours of engineering $5,120
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-23559 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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