CVE-2026-19248 in Qt
Summary
by MITRE • 09/16/2026
QDomDocument XML parsing is vulnerable to a remotely-triggerable denial-of-service crash when processing untrusted input.
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Analysis
by VulDB Data Team • 09/16/2026
The vulnerability in QDomDocument represents a critical flaw within the Qt framework's Extensible Markup Language (XML) parsing engine, specifically affecting the handling of malformed or maliciously crafted XML documents. As a widely used C++ library for cross-platform application development, Qt is frequently employed to process data from external sources, including web services and file uploads. When an attacker submits untrusted input containing specific structural anomalies in the XML document, the QDomDocument parser fails to handle edge cases related to node hierarchy or character encoding correctly. This failure triggers a memory corruption error, typically manifesting as a null pointer dereference or heap buffer overflow, which causes the application process to terminate abruptly. Because this crash can be triggered remotely via network requests that deliver the malicious XML payload, it constitutes a significant availability risk for any service relying on Qt-based components to parse incoming data streams without rigorous pre-validation.
From a technical perspective, the root cause lies in insufficient validation of input structure before processing or inadequate error handling during the traversal of the document object model tree. The parser likely attempts to access memory locations that have not been properly allocated or initialized when encountering specific malformed sequences, such as deeply nested elements with invalid namespaces or improperly escaped characters. This behavior aligns closely with CWE-400, which describes Uncontrolled Resource Consumption leading to denial-of-service conditions through resource exhaustion or crashes. Furthermore, the vulnerability can be mapped to MITRE ATT&CK technique T1496, Host Denial of Service, where an adversary exploits a software flaw to disrupt service availability without necessarily gaining unauthorized access to data or system controls. The remote nature of the exploit means that no authentication is required for an attacker to trigger this condition, lowering the barrier for entry and increasing the potential impact on public-facing applications.
The operational impact of this vulnerability extends beyond simple application crashes. In server-side environments, a successful exploitation can lead to service downtime, requiring manual intervention or automatic restarts which may result in data loss if transactions are not properly committed before the crash occurs. For client-side applications, repeated exposure could degrade user experience and potentially expose sensitive information stored in memory prior to termination if core dumps are generated and accessible. The lack of robust input sanitization means that any system integrating Qt for XML processing is inherently vulnerable unless compensating controls are implemented at the network or application layer. This includes validating content types, limiting payload sizes, and employing allow-listing strategies for expected XML structures before they reach the QDomDocument parser.
Mitigation requires a multi-layered defense strategy focusing on input validation and secure coding practices. Developers should implement strict schema validation using DTDs or XSD files to ensure that incoming XML conforms to predefined structural rules before passing it to the parsing engine. Additionally, integrating third-party sanitization libraries designed specifically for XML processing can help filter out dangerous patterns such as entity expansion attacks or malformed node references. Upgrading to patched versions of the Qt framework where this issue has been resolved is essential if available. Network-level protections like Web Application Firewalls should be configured to detect and block anomalous XML payloads based on size, complexity, and known malicious signatures. Regular security audits focusing on external component dependencies are crucial to identifying similar vulnerabilities in other libraries that handle untrusted data inputs.