CVE-2025-66577 affects cpp-httplib, a widely used C++11 single-file header-only HTTP/HTTPS library, in versions prior to 0.27.0. The vulnerability arises from improper output neutralization for logs (CWE-117) and insufficient validation of client IP headers (CWE-807). Specifically, the get_client_ip() function in docker/main.cc accepts attacker-controlled HTTP headers such as X-Forwarded-For and X-Real-IP without validation. This allows an attacker to inject arbitrary IP addresses into server access and error logs (e.g., nginx_access_logger and nginx_error_logger). The consequence is log poisoning, where logs contain falsified client IPs, undermining the reliability of logs for security monitoring, auditing, and authorization decisions. Attackers can exploit this to evade detection, misattribute malicious activity, or confuse incident responders. The vulnerability does not require authentication or user interaction and can be exploited remotely over the network. Although no known exploits are reported in the wild, the flaw is significant for environments relying on accurate logging for security and compliance. The issue is resolved in cpp-httplib version 0.27.0 by properly sanitizing or ignoring untrusted client IP headers before logging. Organizations using vulnerable versions should prioritize upgrading and review their logging and IP header handling policies to prevent similar issues.

For European organizations, this vulnerability primarily impacts the integrity and trustworthiness of security logs, which are critical for incident detection, forensic analysis, and compliance with regulations such as GDPR and NIS Directive. Spoofed IP addresses in logs can lead to misattribution of malicious activities, complicate threat hunting, and delay response efforts. In regulated industries like finance, healthcare, and critical infrastructure, inaccurate logs may result in non-compliance penalties or failure to meet audit requirements. Although the vulnerability does not directly compromise data confidentiality or system availability, the indirect impact on security operations and trust in monitoring systems can be significant. Organizations relying on cpp-httplib in web servers, proxies, or microservices are at risk, especially if they use the affected versions without additional IP validation. Attackers could leverage this flaw to cover tracks after reconnaissance or exploitation, increasing the overall risk posture.

1. Upgrade cpp-httplib to version 0.27.0 or later immediately to apply the official fix. 2. Implement strict validation and sanitization of HTTP headers that influence client IP determination, such as X-Forwarded-For and X-Real-IP, ensuring only trusted proxies can set these headers. 3. Configure web servers and proxies to overwrite or ignore untrusted client IP headers before passing requests to backend services using cpp-httplib. 4. Enhance logging mechanisms to include additional metadata (e.g., connection source IP, proxy chain) to cross-verify client IP information. 5. Conduct regular log integrity checks and anomaly detection to identify suspicious IP spoofing or log tampering attempts. 6. Review authorization logic that depends on client IP addresses to avoid relying solely on potentially spoofed headers. 7. Educate development and operations teams about the risks of trusting client-supplied headers and enforce secure coding practices around input validation. 8. For containerized environments, ensure that network policies and ingress controllers properly handle and sanitize forwarded headers.