CVE-2024-3096 is a vulnerability in the PHP language's password verification mechanism affecting versions 8.1.* before 8.1.28, 8.2.* before 8.2.18, and 8.3.* before 8.3.5. The issue arises when a password hash generated by password_hash() starts with a null byte (\x00). Under these conditions, calling password_verify() with an empty string as the password incorrectly returns true, effectively bypassing authentication. This is due to improper input validation (CWE-20) in the password verification logic, where the presence of a null byte at the start of the stored hash causes the function to misinterpret the input, leading to a false positive match. The vulnerability allows an attacker to authenticate as any user whose password hash begins with a null byte without knowing the actual password. Exploitation requires no privileges but does require the attacker to interact with the authentication mechanism, typically by submitting a blank password during login. The vulnerability impacts confidentiality by allowing unauthorized access but does not affect data integrity or system availability. No public exploits have been reported yet, but the vulnerability has a CVSS 3.1 base score of 6.5 (medium severity), reflecting the ease of remote exploitation and the potential impact on sensitive data. The flaw affects a broad range of PHP versions widely deployed in web applications globally, including many European organizations. The root cause is improper input validation in the password verification function, which can be mitigated by updating PHP to patched versions where this logic is corrected.

For European organizations, this vulnerability poses a significant risk to the confidentiality of user accounts and sensitive data. Attackers can bypass authentication controls by exploiting the null byte prefix condition, potentially gaining unauthorized access to web applications, internal systems, or administrative interfaces that rely on PHP's password_hash() and password_verify() functions. This can lead to data breaches, unauthorized data access, and further lateral movement within networks. Sectors such as finance, healthcare, government, and critical infrastructure are particularly at risk due to the sensitive nature of their data and the widespread use of PHP in their web applications. The vulnerability does not directly affect system integrity or availability but can be a stepping stone for more severe attacks if combined with other vulnerabilities or misconfigurations. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits given the public disclosure. Organizations failing to patch promptly may face compliance issues with data protection regulations like GDPR if unauthorized access leads to data exposure.

European organizations should immediately upgrade PHP to versions 8.1.28, 8.2.18, or 8.3.5 or later, where this vulnerability is fixed. In addition to patching, organizations should audit their user databases to identify any password hashes starting with a null byte and reset those passwords to prevent exploitation. Implement additional authentication controls such as multi-factor authentication (MFA) to reduce the risk of unauthorized access even if password verification is bypassed. Review and harden input validation and sanitization processes in authentication workflows to prevent malformed or malicious inputs. Monitor authentication logs for unusual login attempts with blank passwords or other anomalous patterns. Conduct penetration testing focused on authentication bypass scenarios to validate the effectiveness of mitigations. Finally, ensure that development teams are aware of this vulnerability and avoid creating password hashes with null byte prefixes in custom implementations.