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Uncontrolled Search Path (DLL Hijack)Weakness · CWE-427

CVE-2026-21661

HIGH · 8.4 CVSS v4.0 Published 2026-05-06
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
86/100
Remediation priority · High
Zero-click

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
Uncontrolled Search Path Element vulnerability in JohnsonControls AC2000 on Windows allows Leveraging/Manipulating Configuration File Search Paths. This issue affects AC2000: from 10.6 before release 10, from 11.0 before release 9, from 12 before release 3.

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

The AC2000 application on Windows uses a search path to locate configuration files, but does not properly control or validate this path. An attacker with local access can manipulate the search path or place malicious configuration files in locations the application searches, causing arbitrary code execution when the application loads these files.

MitigationUpdate AC2000 to the patched releases (10.6.10, 11.0.9, or 12.3 depending on version branch). Until patched, restrict filesystem permissions on directories in the search path and ensure the application runs from secure, controlled locations.

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
Low
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/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. Locate AC2000 installation
    Search for AC2000 installation directories (commonly in Program Files or Program Files (x86)) or check registry keys under HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\ and HKEY_LOCAL_MACHINE\SOFTWARE for entries containing 'AC2000'
    Affected if AC2000 application is found on the system
  2. Identify installed version
    Examine the AC2000 executable (ac2000.exe or similar) right-click Properties > Details, or check version info in the program's installation directory
    Affected if Version is 10.x below 10.6.10, 11.x below 11.0.9, or 12.x below 12.3
  3. Determine configuration file search path
    Review AC2000 documentation, configuration files, or application logs for settings that define where configuration files are loaded from; common locations include the application directory, user profile, or working directory
    Affected if The application uses a configurable or relative search path to locate config files
  4. Inspect search path directories for unauthorized config files
    Manually examine all directories in the search path for unexpected or recently created configuration files (XML, INI, CFG, or proprietary config formats) that do not belong to the legitimate AC2000 installation
    Affected if Unexpected configuration files are present in directories the application searches
  5. Check filesystem permissions on search path directories
    Right-click each directory in the search path > Properties > Security tab, or run 'icacls [directory]' from command prompt to review which users and groups have Write or Modify permissions
    Affected if Low-privilege users or untrusted accounts have Write access to directories in the search path

The system is affected if AC2000 version is below 10.6.10/11.0.9/12.3 AND the search path directories have weak permissions allowing unauthorized placement of configuration files.

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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Update AC2000 to the patched releases (10.6.10, 11.0.9, or 12.3 depending on version branch). Until patched, restrict filesystem permissions on directories in the search path and ensure the application runs from secure, controlled locations.

Recommended fix Moderate confidence

AC2000 10.6 to release 10, AC2000 11.0 to release 9, or AC2000 12 to release 3 (depending on your current major version)

  1. Identify the currently installed AC2000 version (10.6.x, 11.0.x, or 12.x)
  2. For AC2000 version 10.6.x: upgrade to release 10
  3. For AC2000 version 11.0.x: upgrade to release 9
  4. For AC2000 version 12.x: upgrade to release 3
  5. Obtain the appropriate updated installer from JohnsonControls official support channels
  6. Apply the upgrade following standard JohnsonControls installation procedures
  7. Verify the version has been correctly updated after installation

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2026-21661 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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