CVE-2025-5455 is a high-severity vulnerability identified in the Qt framework, specifically within the private API function qDecodeDataUrl() in the QtCore module. This function is utilized internally by components such as QTextDocument and QNetworkReply, and may also be invoked in user applications that leverage Qt for handling data URLs. The vulnerability arises from improper input validation (CWE-20) when processing malformed data URLs, particularly those containing a 'charset' parameter without an assigned value (e.g., 'data:charset,'). When Qt is compiled with assertions enabled, encountering such malformed input triggers an assertion failure, causing the application to abort unexpectedly. This results in a denial of service (DoS) condition. The affected versions include Qt up to 5.15.18, all versions from 6.0.0 through 6.5.8, 6.6.0 through 6.8.3, and 6.9.0. The issue has been addressed in Qt versions 5.15.19, 6.5.9, 6.8.4, and 6.9.1. The CVSS 4.0 base score of 8.4 reflects the vulnerability's high impact, with network attack vector, low attack complexity, no privileges required, but requiring user interaction. The vulnerability does not compromise confidentiality or integrity but severely impacts availability by causing application crashes. No known exploits are currently reported in the wild. The vulnerability's root cause is insufficient validation of input parameters in the qDecodeDataUrl() function, which should be hardened to handle malformed data gracefully without triggering assertions.

For European organizations, the impact of CVE-2025-5455 can be significant, especially for those relying on Qt-based applications or custom software built on the Qt framework. The denial of service triggered by malformed data URLs can disrupt critical services, particularly in sectors such as finance, healthcare, telecommunications, and industrial control systems where Qt is commonly used for GUI and network communication layers. The requirement for user interaction implies that exploitation may occur through crafted URLs delivered via email, web content, or other user-facing interfaces, potentially leading to application crashes and service interruptions. This can result in operational downtime, loss of productivity, and potential reputational damage. Additionally, embedded systems and IoT devices in European infrastructure using vulnerable Qt versions may be susceptible, affecting availability of essential services. Although no known exploits exist yet, the ease of triggering the DoS via network vectors and low complexity makes it a credible threat that organizations should proactively address.

European organizations should prioritize upgrading Qt libraries to the fixed versions: 5.15.19, 6.5.9, 6.8.4, or 6.9.1 depending on their current deployment. For applications where immediate upgrade is not feasible, implement input validation and sanitization at the application layer to detect and reject malformed data URLs before they reach the vulnerable qDecodeDataUrl() function. Employ runtime monitoring and anomaly detection to identify unexpected application crashes potentially caused by malformed inputs. Disable assertions in production builds if possible, as assertions trigger the abort, although this is a temporary workaround and not a substitute for patching. Conduct thorough code audits for any custom usage of qDecodeDataUrl() or similar data URL processing functions to ensure robust error handling. Additionally, educate users and administrators about the risks of interacting with untrusted URLs and implement network-level filtering to block suspicious data URL patterns. Maintain an incident response plan to quickly address any DoS incidents arising from this vulnerability.