CVE-2024-2756 is a vulnerability in the PHP language affecting versions 8.1.*, 8.2.*, and 8.3.*. It arises from an incomplete remediation of CVE-2022-31629, which involved improper input validation (CWE-20). The flaw allows attackers operating within the network or on the same site to set cookies that are insecure but are incorrectly accepted by PHP applications as __Host- or __Secure- cookies. These cookie prefixes are intended to enforce strict security policies: __Host- cookies must be set from a secure origin, have no Domain attribute, and use the Secure attribute; __Secure- cookies require the Secure attribute. By bypassing these checks, attackers can inject cookies that PHP treats as highly trusted, potentially enabling cookie poisoning or session fixation attacks. This compromises the integrity of cookie-based security mechanisms but does not directly expose confidential data or disrupt availability. Exploitation requires no privileges but does require user interaction, such as visiting a malicious site or interacting with a crafted request. No known exploits have been reported in the wild, and no official patches have been linked yet, indicating that remediation is pending. The vulnerability is scored 6.5 on the CVSS v3.1 scale, reflecting a medium severity level due to its impact on integrity and ease of exploitation without privileges. Organizations using affected PHP versions in web-facing applications should prioritize assessment and mitigation to prevent potential abuse.

For European organizations, the primary impact of CVE-2024-2756 is on the integrity of web application security controls relying on cookie attributes for session management and access control. Attackers can exploit this vulnerability to set insecure cookies that PHP treats as secure, potentially enabling session fixation, privilege escalation, or bypass of security policies enforced via cookies. This could lead to unauthorized actions performed under a victim's session or manipulation of user state. While confidentiality and availability are not directly affected, the integrity breach can facilitate further attacks or fraud. Organizations in sectors with high web application exposure, such as finance, e-commerce, government, and healthcare, face increased risk. The lack of known exploits reduces immediate threat but does not eliminate the risk of future exploitation. The vulnerability's presence in widely deployed PHP versions means many European websites and services could be affected, especially those that have not updated PHP or implemented additional cookie security measures.

1. Monitor official PHP channels for patches addressing CVE-2024-2756 and apply them promptly once released. 2. Conduct a thorough audit of all web applications using affected PHP versions to identify usage of __Host- and __Secure- cookies and verify correct handling and validation of cookie attributes. 3. Implement server-side validation to reject or sanitize cookies that do not conform to expected security attributes, preventing acceptance of insecure cookies masquerading as secure. 4. Use web application firewalls (WAFs) to detect and block suspicious cookie-setting attempts that exploit this vulnerability. 5. Educate developers and administrators about the importance of proper cookie attribute enforcement and the risks posed by this vulnerability. 6. Where feasible, upgrade PHP to versions beyond 8.3.* once patches are available or consider temporary mitigations such as disabling vulnerable cookie handling features. 7. Employ Content Security Policy (CSP) and SameSite cookie attributes to reduce the risk of cross-site attacks that could facilitate exploitation. 8. Regularly review logs for unusual cookie-setting patterns or repeated failed attempts to exploit this vulnerability.