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Home / Blog / PHP 5.6
Security Advisory

PHP 5.6 Security: 198 CVEs & Critical Vulnerabilities Explained

📅 June 07, 2026 ·⏱ 5 min read ·🔒 SiteRecipe Security Team
714 websites still running PHP 5.6  → View full list
198
Total
66
Critical
90
High
41
Medium
1
Low

PHP 5.6 is an outdated version that poses serious security risks to your website. With 198 documented CVEs—including 66 critical vulnerabilities—running this version exposes your site to remote code execution, data breaches, and denial-of-service attacks. Major vulnerabilities in WDDX, SOAP, and SPL extensions can be exploited by attackers to compromise your entire application.

Unfortunately, 714 websites are still using PHP 5.6, many without realizing the danger. These websites are prime targets for cybercriminals who actively exploit known vulnerabilities. If your site is among them, immediate action is required to protect your data, users, and business reputation.

This comprehensive guide explains what PHP 5.6's vulnerabilities mean, how to check if you're affected, and the exact steps to upgrade to a secure version.

What is Php 5.6?

PHP 5.6 is an older server-side programming language version that powers the backend of millions of websites. Released in 2014, it was designed to process code on your web server and generate the pages visitors see in their browsers. Think of it as the engine that makes your website function—handling databases, user logins, form submissions, and content delivery.

However, PHP 5.6 reached end-of-life in January 2019, meaning it no longer receives security updates from developers. This is critical because cybersecurity is an ongoing process. As new threats emerge, software developers release patches to fix vulnerabilities. When a version stops receiving updates, every newly discovered weakness becomes a permanent liability for websites still using it.

Key Vulnerabilities in Php 5.6

198 CVEs found. The most critical are explained below.

CRITICAL CVE-2016-3141 9.8/10 · CVSS v3.0 ⏱ Immediate
WDDX Data Processing Crash Vulnerability

PHP's WDDX extension (used to process certain data formats) has a flaw where it doesn't properly clean up memory after use. When someone sends specially crafted XML data to your website, it can cause the application to crash or behave unpredictably.

Impact: Your website could crash or stop responding to visitors. In worst cases, attackers might be able to take control of your server or access sensitive data.

↗ View on NVD
CRITICAL CVE-2015-4116 9.8/10 · CVSS v3.0 ⏱ Immediate
Heap Data Structure Memory Safety Flaw

PHP's SplMinHeap function (used for organizing data) has a memory management bug. An attacker can exploit this flaw by sending requests that trigger this specific function, potentially taking over your server.

Impact: Attackers could execute malicious code on your server, leading to complete compromise of your website and data theft.

↗ View on NVD
CRITICAL CVE-2015-4599 9.8/10 · CVSS v3.0 ⏱ Immediate
SOAP Protocol Error Message Information Leak

PHP's SOAP functionality (used for web services) improperly handles error messages. When given unexpected data, it can expose sensitive internal information about your system, crash your application, or allow code execution.

Impact: Attackers could learn details about your server setup, crash your application, or potentially gain control of your server.

↗ View on NVD
CRITICAL CVE-2015-4600 9.8/10 · CVSS v3.0 ⏱ Immediate
SOAP Client Type Handling Vulnerability

PHP's SOAP client (used to communicate with external web services) doesn't properly validate data types. Attackers can send malformed data that causes your application to crash or execute malicious code.

Impact: Your website could crash, or attackers could execute arbitrary code and take control of your server.

↗ View on NVD
CRITICAL CVE-2015-4601 9.8/10 · CVSS v3.0 ⏱ Immediate
SOAP Type Confusion in Multiple Components

Multiple parts of PHP's SOAP processing have flaws where they mishandle unexpected data types. This can lead to application crashes or code execution when attackers send specially crafted requests.

Impact: Your application could crash repeatedly, or attackers could execute code on your server.

↗ View on NVD
CRITICAL CVE-2015-4602 9.8/10 · CVSS v3.0 ⏱ Immediate
Incomplete Class Object Type Confusion

PHP's object handling has a flaw where it doesn't properly validate data types when processing incomplete class objects. Attackers can exploit this to crash your application or execute code.

Impact: Your website could become unstable or attackers could gain unauthorized access to your server.

↗ View on NVD

Additional Vulnerabilities (192 more)

Showing first 10 of 192. View all on NVD ↗

CVE IDSeverityScore PublishedDescription
CVE-2015-4603 CRITICAL 9.8 2016-05-16 The exception::getTraceAsString function in Zend/zend_exceptions.c in PHP before 5.4.40, 5.5.x before 5.5.24, and 5.6.x before 5.6.8 allows remote attackers to execute arbitrary c…
CVE-2015-4642 CRITICAL 9.8 2016-05-16 The escapeshellarg function in ext/standard/exec.c in PHP before 5.4.42, 5.5.x before 5.5.26, and 5.6.x before 5.6.10 on Windows allows remote attackers to execute arbitrary OS co…
CVE-2015-4643 CRITICAL 9.8 2016-05-16 Integer overflow in the ftp_genlist function in ext/ftp/ftp.c in PHP before 5.4.42, 5.5.x before 5.5.26, and 5.6.x before 5.6.10 allows remote FTP servers to execute arbitrary cod…
CVE-2015-5589 CRITICAL 9.8 2016-05-16 The phar_convert_to_other function in ext/phar/phar_object.c in PHP before 5.4.43, 5.5.x before 5.5.27, and 5.6.x before 5.6.11 does not validate a file pointer before a close ope…
CVE-2015-6834 CRITICAL 9.8 2016-05-16 Multiple use-after-free vulnerabilities in PHP before 5.4.45, 5.5.x before 5.5.29, and 5.6.x before 5.6.13 allow remote attackers to execute arbitrary code via vectors related to …
CVE-2015-6835 CRITICAL 9.8 2016-05-16 The session deserializer in PHP before 5.4.45, 5.5.x before 5.5.29, and 5.6.x before 5.6.13 mishandles multiple php_var_unserialize calls, which allow remote attackers to execute …
CVE-2015-8835 CRITICAL 9.8 2016-05-16 The make_http_soap_request function in ext/soap/php_http.c in PHP before 5.4.44, 5.5.x before 5.5.28, and 5.6.x before 5.6.12 does not properly retrieve keys, which allows remote …
CVE-2016-2554 CRITICAL 9.8 2016-05-16 Stack-based buffer overflow in ext/phar/tar.c in PHP before 5.5.32, 5.6.x before 5.6.18, and 7.x before 7.0.3 allows remote attackers to cause a denial of service (application cra…
CVE-2016-4071 CRITICAL 9.8 2016-05-20 Format string vulnerability in the php_snmp_error function in ext/snmp/snmp.c in PHP before 5.5.34, 5.6.x before 5.6.20, and 7.x before 7.0.5 allows remote attackers to execute ar…
CVE-2016-4072 CRITICAL 9.8 2016-05-20 The Phar extension in PHP before 5.5.34, 5.6.x before 5.6.20, and 7.x before 7.0.5 allows remote attackers to execute arbitrary code via a crafted filename, as demonstrated by mis…
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Conclusion

PHP 5.6 is no longer safe for production websites. The 198 documented CVEs—particularly the 66 critical vulnerabilities in WDDX, SOAP, and SPL extensions—create an unacceptable security risk. Attackers actively exploit these known weaknesses to steal data, inject malware, and take control of websites. If you're still running PHP 5.6, upgrading isn't optional; it's essential for protecting your business and users.

Don't wait for a breach to force your hand. SiteRecipe.com helps you identify outdated technologies on your website and provides step-by-step guidance to upgrade safely. Our security analysis tool scans for 198+ PHP 5.6 vulnerabilities and gives you a clear roadmap to modern, secure versions. Visit SiteRecipe.com today to run a free security assessment and take the first step toward protecting your website.

Frequently Asked Questions

What does 'end-of-life' mean for PHP 5.6?
End-of-life means the PHP development team no longer releases security patches or updates for PHP 5.6. All newly discovered vulnerabilities remain unpatched forever, making it increasingly dangerous as time passes. Your website becomes more vulnerable each day without protection.
Can I stay on PHP 5.6 if my website works fine?
No. A website that 'works fine' is still extremely vulnerable to attack. 66 critical vulnerabilities allow remote attackers to execute arbitrary code, steal data, and take complete control of your server. Working functionality does not equal security—upgrading is non-negotiable.
Will upgrading PHP break my website?
Most modern websites upgrade smoothly, but older custom code may have compatibility issues. This is why testing in a staging environment first is crucial. Your hosting provider can help identify potential conflicts before the live upgrade, minimizing downtime risk.
Why are there so many CVEs in PHP 5.6?
PHP 5.6 is old enough that every possible weakness has been discovered and documented publicly. Attackers use this list to target outdated sites. Newer PHP versions have fewer known CVEs because they're actively maintained and vulnerabilities are patched before public disclosure.
How can SiteRecipe.com help secure my website?
SiteRecipe.com scans your website to detect outdated technologies like PHP 5.6 and provides specific upgrade recommendations. We give you detailed reports on which vulnerabilities affect you and guide you through safe migration to modern, secure versions.

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DISCLAIMER: This report is based on publicly available CVE data from the National Vulnerability Database (NVD) maintained by NIST. Detection of a technology version does not confirm active exploitation on any specific website. For informational purposes only. SiteRecipe is not responsible for actions taken based on this report. Always consult a qualified security professional.

Source: nvd.nist.gov · Published: June 07, 2026 · SiteRecipe.com