CVE-2022-31684 is a medium-severity vulnerability affecting Reactor Netty HTTP Server versions 1.0.11 through 1.0.23. Reactor Netty is a foundational networking library used in reactive Java applications to build non-blocking HTTP servers and clients. The vulnerability arises when the HTTP server processes invalid HTTP requests and logs request headers at the WARN level. In these cases, the server may inadvertently log sensitive information contained in the request headers, such as valid access tokens. This leakage occurs because the logging mechanism does not adequately sanitize or filter sensitive header data before writing it to server logs. The vulnerability is limited to scenarios where invalid HTTP requests are received and logging at WARN level is enabled, which means normal valid requests are not affected. The CVSS v3.1 base score is 4.3, reflecting a low to medium impact primarily on confidentiality, with no impact on integrity or availability. Exploitation requires an attacker to send crafted invalid HTTP requests to the server and have access to the server logs to retrieve the leaked tokens. There are no known exploits in the wild reported to date. The vulnerability is classified under CWE-532 (Information Exposure Through Log Files). No official patches are linked in the provided data, so mitigation may require upgrading Reactor Netty to a fixed version beyond 1.0.23 or applying custom logging configurations to avoid sensitive data exposure.

For European organizations using Reactor Netty in their web applications or microservices infrastructure, this vulnerability poses a confidentiality risk. If attackers can send invalid HTTP requests and gain access to server logs, they may extract valid access tokens or other sensitive header information, potentially enabling unauthorized access to protected resources or services. This risk is heightened in environments where logs are accessible by multiple personnel or insufficiently protected, such as shared hosting or cloud environments without strict access controls. The impact is limited to confidentiality; integrity and availability are not affected. However, leaked tokens can lead to further compromise of systems or data breaches. Given the widespread use of Java and reactive frameworks in European enterprises, especially in financial, healthcare, and government sectors, the vulnerability could be leveraged to escalate attacks if combined with other weaknesses. The requirement for invalid requests and WARN-level logging reduces the likelihood of exploitation but does not eliminate the risk, especially in complex or misconfigured environments.

European organizations should take the following specific steps to mitigate this vulnerability: 1) Identify all applications and services using Reactor Netty versions 1.0.11 to 1.0.23. 2) Upgrade Reactor Netty to a version later than 1.0.23 where the vulnerability is fixed, or apply vendor-provided patches if available. 3) Review and adjust logging configurations to avoid logging sensitive headers at WARN or higher levels, especially for invalid HTTP requests. Implement custom log filters or sanitization to redact sensitive tokens from logs. 4) Restrict access to server logs strictly to authorized personnel and systems, using role-based access controls and encryption at rest. 5) Monitor logs for unusual invalid HTTP request patterns that might indicate exploitation attempts. 6) Conduct security reviews of token handling and ensure tokens have limited scope and lifetime to minimize impact if leaked. 7) Incorporate this vulnerability into incident response and threat hunting processes to detect potential misuse. These measures go beyond generic advice by focusing on logging practices, token management, and access controls tailored to the nature of this vulnerability.