CVE-2025-1217 is a medium-severity vulnerability affecting multiple recent versions of PHP (8.1.* before 8.1.32, 8.2.* before 8.2.28, 8.3.* before 8.3.19, and 8.4.* before 8.4.5). The vulnerability arises from improper input validation (CWE-20) in the HTTP request module of PHP when parsing HTTP responses from servers. Specifically, the issue involves incorrect parsing of folded HTTP headers, which are headers that span multiple lines and are folded according to HTTP specifications. Due to this improper parsing, PHP may misinterpret the response headers, leading to the use of incorrect headers, MIME types, or other header-related data. This can cause downstream logic errors in applications relying on PHP's HTTP response parsing, potentially resulting in security issues such as content spoofing, incorrect content handling, or bypassing security controls that depend on header values. The vulnerability does not require authentication or user interaction but has a higher attack complexity (AC:H) and only partially impacts confidentiality (R:A) with no impact on integrity or availability. There are no known exploits in the wild at the time of publication, and no official patches have been linked yet. The CVSS 4.0 score is 6.3, indicating a medium severity level. This vulnerability is particularly relevant for web applications and services using PHP's HTTP request functionality to interact with external servers, especially where header values influence security decisions or content rendering.

For European organizations, the impact of CVE-2025-1217 can be significant in environments where PHP is used extensively for web applications, APIs, or middleware that consume HTTP responses from external or internal services. Misinterpretation of HTTP headers can lead to security bypasses such as incorrect MIME type handling, which may facilitate cross-site scripting (XSS) or content injection attacks if malicious actors craft responses with manipulated headers. Additionally, security controls relying on header values (e.g., Content-Security-Policy, CORS headers, or authentication tokens in headers) might be circumvented or rendered ineffective. This can compromise confidentiality by exposing sensitive data or enabling unauthorized access. Although the vulnerability does not directly affect integrity or availability, the indirect effects on application logic and security posture can be impactful. European organizations in sectors such as finance, healthcare, government, and e-commerce, which often rely on PHP-based applications, may face increased risk, especially if they integrate third-party services or microservices that communicate over HTTP. The lack of known exploits suggests a window of opportunity for proactive mitigation before exploitation attempts emerge.

European organizations should prioritize updating PHP to the fixed versions as soon as they become available (8.1.32+, 8.2.28+, 8.3.19+, 8.4.5+). Until patches are released, organizations should implement strict input validation and sanitization on HTTP responses processed by PHP applications, especially those handling folded headers. Employing web application firewalls (WAFs) that can detect and block malformed or suspicious HTTP headers may reduce risk. Developers should audit application code to identify any logic that relies on HTTP header values from external sources and implement additional verification or normalization steps. Monitoring network traffic for unusual or malformed HTTP responses can help detect exploitation attempts. Additionally, organizations should review their dependency on PHP HTTP request modules and consider isolating or sandboxing components that process external HTTP responses to limit potential damage. Regular vulnerability scanning and penetration testing focused on HTTP header handling can further enhance detection and prevention capabilities.