CVE-2026-78253 in Qt Group
Summary
by MITRE • 09/23/2026
Uncontrolled recursion in QXmlStreamReader::readElementText() in Qt Group Qt allows attackers to cause a denial of service (application crash via stack exhaustion) via a crafted XML document.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified involves an uncontrolled recursive function call within the QXmlStreamReader component of the Qt framework, specifically affecting the readElementText method. This class is designed for efficient parsing of well-formed XML documents by providing a fast and easy-to-use interface that reads only what is needed at any given time. However, in this specific implementation, the logic governing how element text content is processed fails to adequately limit recursion depth when encountering nested or self-referential structures within an XML payload. When an attacker crafts an XML document with deeply nested elements or circular references that trigger repeated calls to readElementText without proper termination conditions, it leads to excessive consumption of stack memory resources on the executing system.
From a technical perspective, this flaw represents a classic case of uncontrolled recursion where the application does not enforce a maximum depth limit for parsing operations. As the parser processes each nested tag, it pushes new frames onto the call stack. Because there is no safeguard against excessively deep nesting or recursive structures that mimic valid XML syntax but exploit internal processing logic, the available stack space is rapidly exhausted. This results in a stack overflow condition which typically causes the application to crash abruptly. The impact of this vulnerability is primarily a denial of service scenario where legitimate users are unable to access services relying on Qt-based applications for XML parsing tasks such as configuration file reading, data exchange formats like RSS feeds or SOAP messages, and document processing tools built with Qt libraries.
This issue aligns closely with CWE-675 which describes operations that may cause excessive resource consumption due to uncontrolled recursion. In the context of attack patterns, this vulnerability can be leveraged through techniques associated with ATT&CK T1499 Endpoint Denial of Service where an attacker uses crafted input to exhaust system resources and disrupt service availability. The exploitation does not require authentication or complex privilege escalation since it relies solely on submitting a maliciously structured XML file that triggers the recursive loop during standard parsing operations common in many enterprise applications using Qt for data handling.
Mitigation strategies should focus on implementing strict limits on recursion depth within the QXmlStreamReader implementation if direct modification of source code is feasible, ensuring that any nested element processing respects predefined boundaries to prevent stack exhaustion. For users unable to patch immediately, input validation mechanisms at the application layer can be employed to detect and reject XML documents with excessive nesting levels before they reach the parser. Additionally, deploying runtime protection solutions such as memory corruption detection tools or sandboxing environments may help contain the impact of such crashes by isolating affected processes from critical system resources. Regular updates to Qt libraries are recommended as vendors typically release patches addressing these types of logic flaws in subsequent versions ensuring robust handling of edge cases in XML parsing scenarios.