CVE-2024-9026 is a vulnerability in PHP versions 8.1.* before 8.1.30, 8.2.* before 8.2.24, and 8.3.* before 8.3.12, specifically affecting the PHP-FPM SAPI when configured with catch_workers_output set to yes. This setting captures the output of PHP worker processes for logging purposes. The vulnerability stems from improper neutralization of null byte (NUL) characters in log messages, categorized under CWE-158 and CWE-117, which relate to improper handling of null bytes and improper output neutralization respectively. An attacker with limited privileges (local access with low privileges) can craft log messages containing null bytes that manipulate the final log output, either polluting the logs or removing up to four characters from log entries. When PHP-FPM is configured to send logs to syslog, the vulnerability can be exploited to remove additional log data, further compromising log integrity. This can hinder forensic investigations or security monitoring by corrupting or omitting critical log information. The vulnerability does not allow for confidentiality breaches or denial of service but impacts the integrity of logs, which are essential for incident detection and response. Exploitation requires local access and no user interaction, with low complexity. No public exploits or active exploitation have been reported to date. The issue is resolved in PHP versions 8.1.30, 8.2.24, and 8.3.12 by properly handling null byte characters in log messages to prevent log pollution or truncation.

For European organizations, the primary impact of CVE-2024-9026 lies in the potential degradation of log integrity within PHP-FPM environments. Many European enterprises and public sector entities rely on PHP-based web applications and services, often using PHP-FPM for performance. Compromised logs can obscure malicious activities or operational issues, reducing the effectiveness of security monitoring, incident response, and compliance auditing. This is particularly critical for organizations subject to strict regulatory requirements such as GDPR, NIS Directive, or sector-specific standards that mandate reliable logging. While the vulnerability does not directly expose sensitive data or disrupt service availability, the loss or corruption of log data can delay detection of breaches or insider threats, increasing risk exposure. Attackers with local access could exploit this to cover tracks after gaining foothold, complicating forensic investigations. The impact is more pronounced in environments where PHP-FPM logs are forwarded to centralized syslog servers, as the vulnerability allows further log data removal. Overall, the threat undermines trust in log data integrity, which is foundational for cybersecurity operations in European organizations.

1. Upgrade PHP to the fixed versions: 8.1.30 or later, 8.2.24 or later, or 8.3.12 or later to ensure the vulnerability is patched. 2. Review and harden PHP-FPM configurations, especially the catch_workers_output setting; consider disabling it if not strictly necessary. 3. If using syslog for PHP-FPM logging, verify the integrity and completeness of logs regularly and implement additional log validation mechanisms. 4. Employ host-based intrusion detection systems (HIDS) to monitor for suspicious local activity that could precede exploitation attempts. 5. Restrict local access to PHP-FPM servers to trusted administrators and use strong access controls to minimize the risk of local exploitation. 6. Implement centralized logging with tamper-evident storage to detect any log manipulation attempts. 7. Conduct regular audits of logging infrastructure and ensure that log retention policies comply with regulatory requirements. 8. Educate system administrators about this vulnerability and the importance of timely patching and log integrity monitoring.