Summary
A critical injection vulnerability in the GL-iNet GL-MT3000 router affects the plugins.set_config function exposed via /cgi-bin/glc in the native plugins.so component.
When untrusted input is passed into configuration handling routines without sufficient validation or encoding, a remote attacker may inject crafted data to alter system behavior or execute unintended actions.
Affected context
The issue arises in GL-iNet GL-MT3000 devices (firmware up to 4.4.5) where the web-based management interface exposes native plugin functionality through /cgi-bin/glc.
The plugins.set_config action processes attacker-controlled request parameters as part of plugin configuration logic.
In environments where this interface is reachable from untrusted networks, and request data is not canonically validated or contextually encoded, the vulnerable code path can be reached by remote users.
Exploit preconditions
- Attack surface: HTTP(S) interface on the GL-MT3000 router, specifically requests targeting
/cgi-bin/glcwith actions invokingplugins.set_config. - Required access: Network reachability to the management interface; depending on deployment, this may be from LAN clients, VPN users, or misconfigured WAN exposure.
- Trigger point: Submission of crafted parameters that are passed by
plugins.set_configinto downstream interpreters, configuration engines, or command contexts without strict validation and encoding. - Why exploitation is possible: The plugin configuration routine mixes untrusted input with trusted control data, failing to normalize or constrain it before interpretation, enabling injection into the underlying configuration or execution context.
Why this happens
This vulnerability stems from improper neutralization of special elements when constructing configuration or command-like data from user input.
The plugins.set_config function appears to treat external request parameters as trusted configuration fragments, combining them into downstream strings or structures that are subsequently interpreted by other components.
Under CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component), this pattern occurs when an application fails to escape, encode, or constrain user-supplied values before embedding them in contexts like configuration files, shell commands, or scripting environments.
The additional mapping to CWE-707 (Improper Neutralization) highlights a broader absence of centralized, consistent input sanitization and context-aware encoding, allowing malicious input to alter the meaning of the constructed content and leading to unintended behavior or code execution.
Potential impact
- Remote attackers could alter router configuration, including plugin settings and potentially network policies.
- Arbitrary command or code execution may be possible if injected values are ultimately passed to interpreters (e.g., shell, scripting engines).
- Persistent compromise of the device, including installing or enabling malicious plugins or traffic redirection rules.
- Loss of confidentiality and integrity for network traffic traversing the router, including potential man-in-the-middle scenarios.
- Use of the compromised device as a pivot point for attacks on internal networks or other connected systems.
General mitigation guidance
Effective mitigation focuses on enforcing strict separation between untrusted input and any interpreted or configuration contexts.
Pattern-based safeguards include:
- Introducing centralized, context-aware validation for all plugin-related inputs, limiting allowed characters, value ranges, and structures to a minimal, documented subset.
- Applying appropriate encoding/escaping before embedding user-supplied data into downstream components such as configuration files, system commands, or scripts, ensuring it cannot alter control structures.
- Designing plugin configuration APIs such that clients submit structured, strongly typed data (e.g., fixed JSON schemas) instead of free-form strings that can contain control characters.
- Reducing privilege of the plugin management component so that even if a configuration entry is misused, its ability to modify core system state or execute privileged actions is constrained.
- Isolating plugin execution environments (e.g., via separate processes, sandboxes, or restricted chroot/jails) to limit the blast radius of misconfigured or malicious plugins.
- Restricting access to the management interface to trusted administrative networks and disabling unneeded plugin management endpoints by default.
How teams detect issues like this
Detection typically revolves around identifying unsafe input handling and unusual configuration manipulations.
Common approaches include:
- Static analysis rules that flag concatenation or interpolation of HTTP parameters into configuration or command-building code within native modules like
plugins.so, especially aroundplugins.set_config. - Code review checklists that require explicit justification and documentation whenever user-supplied data is passed into interpreters, configuration engines, or shell commands, with reviewers looking for missing encoding or validation layers.
- Policy-based linting or security gates in build pipelines that enforce the use of vetted input-validation and encoding utilities for all plugin management functions.
- Runtime monitoring of router logs and plugin activity for anomalous configuration changes, unexpected plugin deployments, or sudden shifts in management interface usage patterns.
- Periodic security testing (including fuzzing and negative testing) of web-based configuration endpoints to uncover injection vectors and validate that new code adheres to safe patterns.
