- Qt 6.11
- All Overviews
- Security in Qt
- Qt Shared Security Model
- Qt 6.11.2 Reference Documentation

Security ◦ Handling Untrusted Data

# Qt Shared Security Model

The Qt Shared Security Model defines the distribution of security responsibilities among Qt application developers, the Qt Group and Qt Project as providers of the Qt Framework, and operators or device manufacturers. The model establishes clear expectations regarding responsibility for security across the various layers of the technology stack in a typical Qt application or device.

This page provides guidance for developers building Qt applications and for security researchers reporting security issues in Qt.

## Overview

Security in Qt applications is a shared responsibility. Qt provides secure frameworks and libraries, but the ultimate security of an application depends on how developers use these components and how they handle application-specific concerns.

A typical Qt application can be visualized as a stack:

## Roles and responsibilities

### Responsibilities of the application developer

You, as an application developer, are responsible for the security of the application-specific code, assets, and configuration. You also assume responsibility for any standalone third-party libraries that are shipped with the application.

Qt aims to provide a user-friendly, safe-by-default API. However, it is your responsibility to use the API diligently, and for example check for error conditions and handle them appropriately. For an overview of security considerations when using Qt, see Security in Qt.

Review your application in terms of which data sources are trusted and which are untrusted. Make sure to validate and sanitize untrusted data using appropriate Qt APIs. See also Handling Untrusted Data for more information.

Plan mechanisms to update the application and apply Qt security updates in a timely manner. Follow Qt releases and security announcements, and update Qt accordingly. Also, ensure that you obtain Qt from a trusted source.

If you ship Qt as part of your application, limit the number of libraries and plugins to reduce the attack surface. For example, ship only the image plugins for the formats you actually need.

When switching Qt defaults, be careful that you don't accidentally disable security features or weaken security guarantees. For example, don't disable SSL/TLS certificate validation unless you have a very good reason to do so. Another example is changes to the Qt search paths, for instance through qt.conf. Make sure all paths are trustworthy.

### Responsibilities of Qt

The Qt Group and Qt Project are responsible for the security of the Qt framework itself, including all officially distributed binaries and redistributables. This includes maintaining and updating any third-party components bundled with Qt libraries and plugins, tracking known vulnerabilities, and providing timely fixes.

Qt aims to provide APIs that are secure by default. Common use cases are designed to minimize the risk of misuse, while operations with security implications require explicit developer action.

Qt provides APIs a developer can use to process and validate data from untrusted sources, such as user input, network communication, or external files. Where it is unreasonable for a developer to implement their own validation, Qt provides built-in validation. For example, Qt's image decoders are designed to securely parse image files. There might be APIs though where neither is possible or reasonable; in these cases, the documentation warns about calling the API with untrusted data.

### Responsibilities of operator or device manufacturer

Both Qt and the application have to rely on the security and integrity of the operating environment (hardware, operating system, and services). On desktop systems, this is typically the responsibility of the operator of the application; for example, by keeping the operating system up-to-date. On embedded devices, it is the responsibility of the device manufacturer.

This includes the process environment that the Qt application is running in. For instance, all desktop applications expect the directories in the `PATH` environment variable to be trustworthy.

## Security issue acceptance criteria

Security researchers should use the following guidelines when determining whether a potential security issue should be reported to the Qt Project:

### Issues Qt will accept

The Qt Group and the Qt Project accept security issues that:

- Affect Qt framework code: Vulnerabilities in Qt's own code, including memory corruption bugs, type confusion, use-after-free, buffer overflows, and similar memory safety issues in Qt libraries.
- Affect bundled third-party components: Security vulnerabilities in third-party libraries and components that are bundled with Qt.
- Break security guarantees: Issues where Qt APIs fail to provide documented security guarantees or violate reasonable security expectations for security-critical APIs.
- Affect default configurations: Security issues in default Qt configurations that could affect typical applications without developer intervention.

Qt also expects security issues to have a realistic attack scenario. Issues that cannot be exploited in practice or require unrealistic conditions will be treated as defects, but not considered security issues.

### Issues Qt will not accept

The Qt Group and Qt Project do not accept reports for security issues that:

- Require insecure application code: Issues that only manifest when the application developer writes insecure code or misuses Qt APIs in ways that are not in line with documentation or established best practices.
- Are based on application-specific logic flaws: Security issues in application-specific logic, such as authentication bypasses, authorization flaws, or business logic vulnerabilities.
- Depend on malicious application code: Issues that require the application to execute malicious code. Qt assumes that application developers control their own code and resources.
- Require malicious QML/JavaScript: Qt Qml assumes all QML and JavaScript code is provided by the application developer. Running untrusted QML code is not supported. See Handling Untrusted Data for more information.
- Depend on issues in operating environment: Vulnerabilities in the underlying operating system, hardware, or system libraries that are not bundled with Qt.
- Depend on an insecure process environment: Attacks that require an insecure process environment, such as untrusted directories in the `PATH` or `QT_PLUGIN_PATH` environment variables, are outside the scope of Qt's security responsibility.

Furthermore, reports for cybersecurity issues need a realistic attack scenario that

- Crosses a security boundary: For example, issues which require an attacker already having access to the application process and being able to execute code are not considered security issues.
- Is not based on social engineering: Issues that primarily rely on social engineering or tricking users rather than technical vulnerabilities in Qt.

## Frequently asked questions

### Who is responsible for validating user input?

The application developer is responsible for validating user input. While Qt provides validation tools (see QValidator and QML Validators), it is the application's responsibility to use these tools appropriately and implement application-specific validation logic.

### Is Qt responsible for SQL injection vulnerabilities?

No. SQL injection vulnerabilities typically result from improper use of SQL APIs. Developers must use parameterized queries and prepared statements (such as QSqlQuery::prepare) to prevent SQL injection. However, Qt is responsible for ensuring that these secure APIs function correctly.

### What about cross-site scripting (XSS) in Qt applications?

XSS prevention is primarily the application developer's responsibility. Developers must properly sanitize and escape data when displaying untrusted content, especially in web views or rich text components. Qt provides APIs like QString::toHtmlEscaped to assist with this, and Qt WebEngine implements web platform security features, but the application must use these correctly.

### Who handles encryption and secure communications?

Both Qt and the application developer share responsibility:

- Qt provides secure networking APIs (QSslSocket, QNetworkAccessManager) with secure defaults.
- Application developers must properly use these APIs, implement certificate validation, manage keys securely, and handle sensitive data appropriately. If they bundle OpenSSL with the application, it is also their responsibility to keep it up to date and apply security patches.

### Is loading untrusted QML code a security issue?

Running untrusted QML code is explicitly not supported and is considered a misuse of the QML engine. Qt Qml is designed with the assumption that all QML and JavaScript code is trusted and provided by the application developer. If your application needs to load untrusted content, use appropriate sandboxing mechanisms or alternative approaches, like a custom Domain-Specific Language (DSL).

### What about image file vulnerabilities?

Qt considers image decoding a security-critical API and takes responsibility for securely parsing image files from untrusted sources. Security issues in Qt's image decoders (buffer overflows, crashes, and similar issues) should be reported to the Qt Group or Qt Project. However, applications must still validate image sources, handle large images appropriately, and manage application-specific image security concerns.

### How do I report a security issue?

See Reporting Security Issues in the Security in Qt page for detailed instructions on reporting security issues to the Qt Project.

### What versions of Qt receive security updates?

Security updates are provided for supported Qt versions. See Qt Releases for information about supported versions and Extended Security Maintenance for end-of-support versions.

## Additional Resources

For more information about security in Qt, see:

- Security in Qt
- Handling Untrusted Data
- Application Permissions
- QUIP 15 Qt Project Security Policy
- List of Known Vulnerabilities in Qt Products

Security ◦ Handling Untrusted Data