CVE-2026-94370 in for MCUs
Summary
by MITRE • 10/14/2026
A defect in the Qt for MCUs core string handling causes heap memory corruption. When an application passes text into Qt Quick Ultralite using the public Qul::String interface type, and that text is held in a std::string, the conversion to the internal string type copies the pointer without taking ownership of it. Two objects then release the same memory, producing a double free, an invalid free, or a use-after-free.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified involves a critical flaw within the Qt for MCUs core library's string handling mechanism, specifically affecting the Qul::String interface used in conjunction with Qt Quick Ultralite applications. This defect manifests as heap memory corruption due to improper management of object lifecycles and pointer ownership during type conversion processes. The root cause lies in how the internal representation of strings is constructed when data originates from a standard C++ std::string container. Instead of performing a deep copy or explicitly transferring ownership of the underlying buffer, the implementation performs a shallow copy by merely duplicating the raw memory pointer. This design oversight creates a scenario where two distinct objects believe they are solely responsible for managing and eventually releasing the same block of heap-allocated memory.
From an operational perspective, this architectural flaw leads to severe stability issues and potential security risks depending on how the corrupted memory is subsequently accessed or freed. When both the original std::string object and the newly created Qul::String instance go out of scope or are explicitly destroyed, they each attempt to deallocate the same memory address. This results in a double free condition, which typically causes immediate application crashes due to heap metadata corruption detected by the allocator. Alternatively, if one pointer is freed while the other remains active and subsequently accesses that memory region, it triggers a use-after-free vulnerability. Use-after-free scenarios are particularly dangerous as they can lead to arbitrary code execution if an attacker can control the data written into the reallocated memory space before the dangling pointer is accessed.
This issue aligns with Common Weakness Enumeration (CWE) categories such as CWE-415, Double Free, and CWE-416, Use After Free. These weaknesses represent fundamental errors in resource management where software fails to properly handle deallocation of dynamically allocated memory. In the context of embedded systems running Qt for MCUs, such vulnerabilities compromise the reliability of real-time applications that depend on consistent memory states. The lack of clear ownership semantics during the conversion from standard library containers to proprietary UI framework types violates best practices for safe C++ programming, particularly regarding RAII (Resource Acquisition Is Initialization) principles which dictate that resources should be tied to object lifetimes and managed automatically without manual intervention or ambiguous sharing.
Mitigation strategies must focus on correcting the memory ownership model within the Qul::String implementation. The most effective fix involves ensuring that when a std::string is converted into an internal Qt Quick Ultralite string type, the framework takes explicit ownership of the data by performing a deep copy rather than copying pointers. Alternatively, if performance constraints necessitate avoiding copies, the interface should enforce move semantics or require the caller to retain responsibility for the original buffer's lifetime until it is no longer needed by the UI layer. Developers integrating Qt Quick Ultralite into their applications should also implement strict code reviews focusing on string handling and consider using static analysis tools capable of detecting double-free and use-after-free patterns in C++ projects. Updating to a patched version of the Qt for MCUs library that resolves this ownership ambiguity is essential for maintaining system integrity and preventing potential exploitation through memory corruption attacks.