PHP version 5.6.40 was the final "security-only" release for the PHP 5.6 branch. As of April 2026, this version has been unsupported for over seven years. Any vulnerabilities discovered after January 2019 remain unpatched by the official PHP development team, posing a severe risk to data integrity and server security. Key Verified Vulnerabilities
Network/Remote. An attacker does not need prior authentication if they can feed input to a vulnerable script handling serialization or object manipulation. How the Vulnerability is Exploited
to look out for. Would you like a list of the most frequent "breaking changes" between PHP 5.6 and 8.x? php version 5640 vulnerabilities verified
Outdated SSL/TLS implementations within the PHP 5.6 core do not support modern encryption standards. Risk Analysis Threat Level Description Critical Full System Compromise Unauthorized access to the underlying OS. High Data Breach Potential theft of database credentials and user info. High Compliance Failure
To truly understand the vulnerability of PHP 5.6.40, it helps to contextualize its timeline. PHP 5.6 officially reached its on December 31, 2018. PHP version 5
PHP version 5.6.40 has several verified vulnerabilities that can have a significant impact on the security of web applications built using this version. By understanding these vulnerabilities and implementing mitigation strategies, developers and system administrators can protect their applications and data from potential attacks. It is essential to stay informed about the latest security patches and best practices to ensure the security and integrity of web applications.
PHP 5.6.40 is a security liability. With verified vulnerabilities allowing for full system compromises, continuing to use it in 2026 is extremely risky. The security, performance, and compliance benefits of upgrading to PHP 8.x make the transition necessary for any serious web project. I can help you: Key Verified Vulnerabilities Network/Remote
CVSS Score: 9.8 (Critical) This critical vulnerability, CVE-2015-4603, is a type confusion issue in the exception::getTraceAsString function. It affects PHP versions prior to 5.6.8, which means all versions of PHP 5.6, including 5.6.40, are vulnerable. Attackers can exploit this flaw over a network without authentication or user interaction to execute arbitrary code, leading to a complete loss of confidentiality, integrity, and availability of the affected system.
Although PHP 5.6 reached End-of-Life (EOL) in 2018, Debian Long Term Support (LTS) maintained the php5 package by backporting security patches to version 5.6.40, resulting in multiple sub-versions (e.g., 5.6.40+dfsg-0+deb8u7 , u11 , u12 ). The analysis of these patches reveals further vulnerabilities that were fixed long after the official EOL:
This vulnerability occurs when the PHP garbage collector fails to properly clean up objects, allowing an attacker to execute arbitrary code on the server. This vulnerability can be exploited to gain RCE and execute malicious code.
Configure strict rulesets to block common PHP exploit payloads, such as known object injection strings and directory traversal attempts.