CVE-2025-6566 is a stack-based buffer overflow vulnerability identified in the Oat++ (also known as oatpp) framework, specifically affecting versions 1.3.0 and 1.3.1. The flaw resides in the deserializeArray function within the src/oatpp/json/Deserializer.cpp file. This function is responsible for deserializing JSON arrays, and improper handling of input data can lead to a stack-based buffer overflow. Such a vulnerability allows an attacker to overwrite adjacent memory on the stack, potentially leading to arbitrary code execution, application crashes, or other undefined behavior. The vulnerability is remotely exploitable without requiring authentication or user interaction, as indicated by the CVSS vector (AV:N/AC:L/PR:N/UI:N). The CVSS 4.0 base score is 6.9, categorized as medium severity. Although no known exploits are currently observed in the wild, the public disclosure of the vulnerability increases the risk of exploitation attempts. The vulnerability impacts the confidentiality, integrity, and availability of applications using the affected Oat++ versions, as successful exploitation could lead to remote code execution or denial of service. Oat++ is a modern C++ web framework used for building high-performance web services and APIs, often deployed in microservices architectures and embedded systems. The vulnerability's presence in a core deserialization function makes it critical for developers and organizations relying on Oat++ to address this issue promptly to prevent potential exploitation.

For European organizations, the impact of CVE-2025-6566 can be significant, especially for those utilizing Oat++ in their web services, APIs, or embedded systems. Exploitation could lead to unauthorized remote code execution, allowing attackers to compromise sensitive data, disrupt service availability, or pivot within internal networks. Industries such as finance, healthcare, telecommunications, and critical infrastructure, which often deploy microservices and high-performance APIs, may face increased risks. The vulnerability could also affect cloud service providers and SaaS platforms based in Europe that incorporate Oat++ in their technology stacks. Given the remote exploitability without authentication, attackers could target exposed endpoints to gain initial access or cause denial of service. This could result in data breaches, operational downtime, regulatory non-compliance (e.g., GDPR), and reputational damage. The medium CVSS score reflects a balance between ease of exploitation and impact; however, the critical nature of buffer overflows and potential for code execution warrants urgent attention.

1. Immediate upgrade: Organizations should upgrade to a patched version of Oat++ once available. If no patch is currently released, consider applying temporary mitigations such as input validation and limiting exposure of deserialization endpoints. 2. Input sanitization: Implement strict validation and sanitization of JSON inputs before they reach the deserializeArray function to prevent malformed or malicious payloads. 3. Runtime protections: Employ compiler-level security features such as stack canaries, Address Space Layout Randomization (ASLR), and Control Flow Integrity (CFI) to mitigate exploitation impact. 4. Network controls: Restrict access to services using Oat++ to trusted networks or VPNs, and deploy Web Application Firewalls (WAFs) with custom rules to detect and block suspicious JSON payloads targeting deserialization. 5. Monitoring and detection: Enable detailed logging and monitor for anomalous behavior or crashes related to JSON deserialization. Use intrusion detection systems to identify potential exploitation attempts. 6. Code review and testing: Conduct thorough security reviews and fuzz testing of deserialization code paths to identify and remediate similar vulnerabilities proactively. 7. Incident response readiness: Prepare response plans for potential exploitation scenarios, including isolating affected systems and forensic analysis.