CVE-2026-19395 in Qt
Summary
by MITRE • 10/05/2026
In Qt for MCUs, a Text element that displays styled text halts the device if an <img> tag in the text contains an attribute with an empty value. The text parser passes the empty value to an internal check that only accepts non-empty values. The check fails and reports an error, and the default error handler halts the device.
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Analysis
by VulDB Data Team • 10/05/2026
The vulnerability identified within Qt for MCUs represents a critical reliability flaw in the embedded web rendering engine, specifically affecting the Text element responsible for displaying styled content. This issue arises when the parser processes HTML-like markup containing image tags where an attribute is defined with an empty value rather than being omitted or assigned valid data. In resource-constrained microcontroller environments, such as those running Qt for MCUs, system stability and deterministic behavior are paramount. The failure to handle this specific edge case in input validation leads directly to a denial of service condition by causing the device to halt unexpectedly. This type of flaw is particularly dangerous because it can be triggered remotely if an attacker controls or influences the content rendered on the display, such as through a web interface served from another part of the networked IoT ecosystem.
From a technical perspective, the root cause lies in insufficient input validation within the text parsing module. When the parser encounters an <img> tag with an attribute set to an empty string, it passes this value directly to an internal verification routine designed exclusively for non-empty values. This logic error results in a failed assertion or check that is not gracefully handled by the application layer. Instead of returning an error code, logging the issue, or displaying a placeholder image, the default error handler configured for these low-level components triggers a system halt. This behavior indicates a lack of robust exception handling and defensive programming practices within the rendering engine's core logic. The vulnerability aligns with CWE-20 Improper Input Validation, as the software fails to verify that user-supplied input meets expected criteria before processing it. Furthermore, because this leads to a crash or hang of the entire device, it also maps to CWE-400 Uncontrolled Resource Consumption in terms of availability impact, and potentially CWE-755 Improper Handling of Unexpected Condition if the error state is not recoverable.
The operational impact of this vulnerability is severe for any deployment relying on Qt for MCUs for user interfaces that accept dynamic or untrusted content. A halted device effectively results in a complete denial of service, requiring a physical reset or power cycle to restore functionality. In industrial control systems, medical devices, or automotive infotainment units where such microcontrollers are prevalent, this can lead to significant downtime, safety risks if the system is part of a critical control loop, and increased maintenance costs due to remote bricking events. Attackers could exploit this by injecting specially crafted HTML content into any input field that gets rendered as styled text, thereby forcing the device into an unresponsive state without needing elevated privileges or complex exploitation techniques beyond simple string injection.
Mitigation strategies must focus on strengthening the validation logic within the Qt for MCUs rendering engine and improving error handling mechanisms at both the library level and the application integration layer. Developers should ensure that all attributes in HTML-like tags are validated to confirm they contain non-empty, well-formed values before being passed to internal processing functions. If an empty value is detected, the parser should either strip the attribute entirely or substitute a default placeholder rather than triggering a fatal error. Additionally, implementing custom error handlers that log the incident and attempt graceful degradation can prevent system halts. For organizations using this framework, applying vendor-provided patches that address this specific parsing flaw is essential. Until such updates are available, restricting input sources to trusted origins and sanitizing all incoming HTML content by stripping or validating attributes before rendering can provide a temporary layer of defense against exploitation attempts targeting this weakness.