CVE-2026-75520 in Domoticz
Summary
by MITRE • 10/28/2026
Domoticz is a free, open source home automation system for Linux, Windows, macOS, and Raspberry Pi. Prior to 2026.3, the `udevices` JSON command handler, `Cmd_UpdateDevices` in `main/WebServerCmds.cpp`, performed no `session.rights` check before invoking a Lua parser script, while its sibling command handlers gate access by role. A low-privilege authenticated user could trigger execution of an existing operator-installed Lua parser script with attacker-controlled input through the `GET /json.htm` endpoint with `type=command` and `param=udevices`. The `script` parameter also lacked a `..` path-traversal guard: `CLuaHandler::executeLuaScript` in `main/LuaHandler.cpp` constructed the filename from the parser directory and the supplied script name before passing it to `luaL_loadfile`. Execution is limited to already-installed valid Lua files; this is not arbitrary code execution, and the advisory states that file-write and upload paths require administrator privileges. This issue is addressed in version 2026.3.
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Analysis
by VulDB Data Team • 10/29/2026
Domoticz serves as a widely deployed open-source home automation platform supporting multiple operating systems including Linux, Windows, macOS, and Raspberry Pi environments. The vulnerability identified within versions prior to 2026.3 resides specifically within the web server command handling logic found in main/WebServerCmds.cpp. This component is responsible for processing incoming JSON commands from authenticated users interacting with the system via its HTTP interface. A critical design flaw exists in the Cmd_UpdateDevices handler, which corresponds to the udevices JSON command type accessed through the GET /json.htm endpoint when param equals udevices. Unlike other sibling command handlers that enforce strict role-based access control by checking session rights before execution, this specific handler fails to perform any authorization verification prior to invoking a Lua parser script. This inconsistency in security enforcement creates an avenue for privilege escalation within the application context.
The technical flaw allows a low-privilege authenticated user to trigger the execution of existing operator-installed Lua parser scripts with attacker-controlled input parameters. The mechanism relies on the CLuaHandler::executeLuaScript function located in main/LuaHandler.cpp, which constructs the filename by concatenating the configured parser directory path with the script name supplied by the user via the script parameter. Crucially, this construction process lacks a guard against path traversal sequences such as double dots. While the advisory notes that execution is limited to valid Lua files already present on the system and does not constitute arbitrary code execution since file write and upload operations require administrator privileges, the ability to execute existing scripts with controlled input remains significant. An attacker can manipulate script parameters to influence how these pre-existing parsers process data, potentially leading to unintended side effects or information disclosure depending on the specific logic within those Lua files.
From an operational impact perspective, this vulnerability enables a low-privilege user to bypass intended access controls and execute administrative-level functions embedded within Lua scripts. Although direct arbitrary code execution is prevented by file system permissions and upload restrictions, the ability to control inputs to existing parsers can lead to unauthorized data manipulation or exposure of sensitive home automation states. This aligns with CWE Category 862 which covers Missing Authorization vulnerabilities where an actor accesses a resource without proper rights assignment. Furthermore, this behavior reflects ATT&CK technique T1078 Valid Accounts as the attacker leverages legitimate credentials but exploits insufficient privilege checks to perform actions beyond their assigned role level. The lack of input validation on path components also touches upon CWE Category 22 Improper Limitation of a Pathname to a Restricted Directory although the primary severity stems from the authorization bypass rather than arbitrary file read capabilities.
Mitigation strategies focus primarily on upgrading the Domoticz installation to version 2026.3 or later where this issue has been addressed by implementing consistent session rights checks across all command handlers including Cmd_UpdateDevices. Administrators should ensure that their deployment pipelines enforce automatic updates for critical security patches in home automation infrastructure. In environments where immediate patching is not feasible, network segmentation can help isolate the Domoticz server from untrusted networks to limit exposure to authenticated attacks. Additionally, reviewing and restricting access to Lua parser directories ensures that only necessary scripts are available for execution reducing the attack surface. Security monitoring should be enhanced to detect unusual patterns of JSON command submissions particularly those involving script parameters which may indicate exploitation attempts against this specific vulnerability vector.