CVE-2025-1217 is a vulnerability classified under CWE-20 (Improper Input Validation) affecting multiple recent PHP versions (8.1.*, 8.2.*, 8.3.*, and 8.4.*). The issue occurs within the HTTP request module of PHP when it parses HTTP response headers received from servers. Specifically, the vulnerability involves incorrect parsing of folded headers — a legacy HTTP feature where headers can be split across multiple lines. Due to improper handling, PHP may misinterpret these folded headers, resulting in the use of incorrect headers or MIME types in subsequent processing. This can lead to downstream effects such as incorrect content handling, potential bypasses of security controls relying on header values, or logic errors in applications that depend on accurate header parsing. The vulnerability has a CVSS v4.0 base score of 6.3, indicating medium severity, with network attack vector, high attack complexity, no privileges required, no user interaction, and limited impact on confidentiality. No known exploits have been reported in the wild as of the publication date. The flaw affects PHP installations that process HTTP responses, which is common in web applications, APIs, and services that rely on PHP for backend logic. The root cause is insufficient validation and parsing logic for folded headers, a deprecated but still occasionally encountered HTTP feature. This vulnerability underscores the importance of robust input validation and adherence to updated HTTP standards in parsing libraries.

For European organizations, the impact of CVE-2025-1217 primarily involves potential misinterpretation of HTTP response headers in PHP-based applications. This can lead to incorrect MIME type handling, which may cause security controls relying on content-type validation to fail, potentially enabling content spoofing or injection attacks. Additionally, misused headers could affect caching, authentication, or session management mechanisms that depend on accurate header data. While the vulnerability does not directly lead to remote code execution or data leakage, it can weaken the security posture of affected applications, increasing the risk of secondary attacks. Organizations running web services, content management systems, or APIs on vulnerable PHP versions are at risk of subtle security issues or application logic errors. Given PHP's widespread use in Europe, especially in SMEs and public sector web infrastructure, the vulnerability could have broad reach. However, the high attack complexity and lack of known exploits reduce immediate risk. Still, attackers could craft malicious HTTP responses to exploit this flaw, especially in environments where PHP acts as an HTTP client or proxy. The vulnerability may also affect compliance with data protection regulations if it leads to unauthorized data exposure or manipulation.

European organizations should prioritize updating PHP to the fixed versions: 8.1.32 or later, 8.2.28 or later, 8.3.19 or later, and 8.4.5 or later. Since no official patches are linked yet, monitoring PHP security advisories and applying updates promptly upon release is critical. In the interim, organizations can implement strict input validation and sanitization on HTTP responses processed by PHP modules, if feasible. Employing web application firewalls (WAFs) to detect and block anomalous HTTP headers or malformed requests/responses may reduce exploitation risk. Reviewing and hardening application logic that depends on HTTP headers, such as MIME type checks, authentication headers, and caching controls, can mitigate impact. Logging and monitoring HTTP response parsing errors or unusual header formats can help detect exploitation attempts. Additionally, reducing the use of folded headers in internal and external HTTP communications by enforcing updated HTTP standards (RFC 7230 and later) can limit exposure. Security teams should conduct code reviews and penetration testing focused on HTTP header handling in PHP applications. Finally, educating developers about the risks of legacy HTTP features and proper input validation is recommended to prevent similar issues.