CVE-2024-39936 is a vulnerability in the HTTP/2 protocol implementation within the Qt framework, affecting multiple versions before 5.15.18, 6.2.13, 6.5.7, and 6.7.3. The root cause is a timing issue where code responsible for making security-relevant decisions about an established connection executes too early, before the encrypted() signal is emitted and processed. The encrypted() signal in Qt indicates that the TLS handshake has completed and the connection is secure. If security checks are performed before this signal, the application may incorrectly assume the connection is secure or apply security policies prematurely, potentially allowing attackers to intercept or manipulate data. The vulnerability is classified under CWE-367 (Time-of-check Time-of-use (TOCTOU) race condition), highlighting the risk of decisions based on stale or incomplete state information. The CVSS 3.1 score of 8.6 reflects a high severity with network attack vector, no privileges required, no user interaction, and a critical impact on confidentiality. No integrity or availability impacts are noted. Although no exploits are currently known in the wild, the widespread use of Qt in desktop, mobile, and embedded applications that utilize HTTP/2 means the attack surface is significant. Attackers could exploit this flaw remotely to gain unauthorized access to sensitive data transmitted over HTTP/2 connections. The vulnerability affects multiple branches of Qt, emphasizing the need for comprehensive patching across all affected versions. The lack of patch links in the provided data suggests patches may be pending or recently released, so organizations should monitor vendor advisories closely. This vulnerability is particularly relevant for applications handling sensitive communications, such as financial, healthcare, or governmental software.

For European organizations, the impact of CVE-2024-39936 can be substantial due to the widespread adoption of Qt in various sectors including automotive, telecommunications, industrial control, and enterprise software. Confidentiality breaches could lead to exposure of sensitive customer data, intellectual property, or internal communications. Given the vulnerability allows remote exploitation without authentication or user interaction, attackers could leverage this flaw to intercept or manipulate encrypted HTTP/2 traffic, undermining trust in secure communications. This could result in regulatory non-compliance under GDPR if personal data is compromised, leading to financial penalties and reputational damage. Critical infrastructure and embedded systems using Qt for secure communication may also be at risk, potentially affecting operational continuity. The high CVSS score and the scope of affected Qt versions indicate a broad attack surface, increasing the likelihood of targeted attacks against European organizations that rely on Qt-based applications. The absence of known exploits currently provides a window for proactive mitigation, but also suggests attackers may develop exploits soon.

1. Monitor official Qt project and vendor advisories for patches addressing CVE-2024-39936 and apply them promptly across all affected versions. 2. Conduct an inventory of all applications and devices using Qt HTTP/2 functionality to identify exposure. 3. Review application code and configurations to ensure that security-relevant decisions are not made before the encrypted() signal or equivalent TLS handshake completion indicators are processed. 4. Implement network-level protections such as Web Application Firewalls (WAFs) that can detect anomalous HTTP/2 traffic patterns potentially exploiting timing issues. 5. Employ TLS inspection and logging to monitor encrypted traffic for suspicious activity, while respecting privacy and compliance requirements. 6. For embedded or IoT devices using Qt, coordinate with vendors to ensure firmware updates are available and deployed. 7. Increase security awareness among development teams about TOCTOU race conditions and secure signal handling in asynchronous frameworks like Qt. 8. Consider temporary mitigations such as disabling HTTP/2 support in Qt-based applications if patching is delayed and risk is high. 9. Perform penetration testing and code reviews focused on connection security state management to detect similar timing vulnerabilities. 10. Maintain incident response readiness to quickly address any exploitation attempts once patches are deployed.