PHP version 5.6.40 was released on January 10, 2019 , as a final security release for the 5.6 branch. While 5.6.40 itself addressed several issues, it has since reached its official End of Life (EOL)
and no longer receives security patches from the PHP development team.
Detailed lists of historical vulnerabilities and CVEs for this version can be found on CVE Details Blog Post: The Hidden Risk of PHP 5.6.40 in 2026 If you are still running PHP 5.6.40
, you are essentially driving a car with a 2019 inspection sticker—it might still run, but it’s no longer safe for the road.
As of April 2026, PHP 5.6.40 has been officially unsupported for over seven years. While it was intended to be the most secure version of the 5.6 series at the time of its release, the threat landscape has evolved drastically since then. Why "Final Security Release" is a Misnomer
When PHP 5.6.40 dropped in early 2019, it was the "last scheduled release". However, "final" doesn't mean "invulnerable." It simply means the PHP team stopped looking for bugs in that branch. Any vulnerability discovered since then—of which there have been many—remains in your environment. Critical Vulnerabilities at a Glance
Systems running PHP 5.6.40 or earlier are susceptible to several high-impact exploits: PHP PHP 5.6.40 security vulnerabilities, CVEs
This page lists vulnerability statistics for CVEs published in the last ten years, if any, for PHP » PHP » 5.6. 40 . CVE Details Unsupported Branches - PHP
You're referring to PHP version 5.6.40, which has several known vulnerabilities. To address these concerns, I'll outline a feature that can help mitigate these issues.
Feature: "PHP Vulnerability Shield"
Description: A PHP module that provides an additional layer of security to prevent exploitation of known vulnerabilities in PHP 5.6.40. This module will:
Key Components:
Implementation:
Example Code:
// Vulnerability Database
$vulnerabilityDB = [
'function_name' => [
'vulnerability_description',
'exploit_pattern',
],
// ...
];
// Request Analyzer
function analyzeRequest($request)
global $vulnerabilityDB;
foreach ($vulnerabilityDB as $function => $vulnerability)
if (preg_match($vulnerability['exploit_pattern'], $request))
// Block the request
return false;
return true;
// Function Disabler
function disableVulnerableFunctions()
global $vulnerabilityDB;
foreach ($vulnerabilityDB as $function => $vulnerability)
// Disable the function
function_exists($function) && eval("unset($$function);");
// Patch Manager
function applyPatch($patch)
// Apply the patch
// ...
Benefits:
This feature can be integrated into existing PHP applications, providing a robust security solution for PHP 5.6.40.
PHP version 5.6.40 was the final security release for the PHP 5.6 branch. While its release in early 2019 fixed several critical issues, it is now officially End of Life (EOL) and has not received official security patches since late 2018. Critical Vulnerabilities Fixed in 5.6.40
Version 5.6.40 was primarily released to address the following critical and high-severity flaws found in earlier 5.6.x versions:
CVE-2019-9021 (Severity: 9.8 Critical): A heap-based buffer over-read in mbstring regular expression functions. A remote attacker could send crafted multibyte sequences to cause a system compromise or crash.
CVE-2019-9023 (Severity: 9.8 Critical): An out-of-bounds read error in the xmlrpc_decode function. Remote attackers could cause memory corruption or information disclosure via a hostile XML-RPC server.
CVE-2019-9020 (Severity: 7.5 High): A heap-based buffer over-read in PHAR reading functions. Attackers could exploit this via crafted file names to disclose sensitive information.
CVE-2019-9024 (Severity: 7.5 High): Another out-of-bounds read in xmlrpc_decode related to base64 decoding. Post-5.6.40 Risks
Because 5.6.40 is the final version of an unsupported branch, any vulnerabilities discovered after its release remain unpatched in official builds. Significant threats include: PHP 5.6: Why you should upgrade - Influential Software
Note on Terminology: The exact string "5640" does not correspond to any official PHP version (e.g., 5.6.40 is a real version, often typed as 5.6.40). Given the context of security research and typos, this article addresses PHP 5.6.40 (the final release of the PHP 5.x branch) and explains how to find verified vulnerability links.
After reviewing the 70+ vulnerabilities linked to PHP 5.6.40, you will understand that reading CVEs is not a solution; upgrading is.
Here is the official migration link from PHP.net:
Link to PHP 8.3 migration guide: https://www.php.net/manual/en/migration83.php
For legacy code compatibility:
phpcompatibility (PHPCS) or rector to automate code upgrades.Instead of browsing a static link, use automated vulnerability scanners that return dynamic results. php version 5640 vulnerabilities link
php -v
PHP 5.6.40, your server is vulnerable to every link in this article.PHP 5.6.40 should NOT be used in production - it has many known, unpatched vulnerabilities. Upgrade to PHP 7.4+ (or PHP 8.x) immediately for security.
In the quiet, humming rows of a forgotten data center, a server named "Old Faithful" still ran a relic: PHP version 5.6.40. Released on January 10, 2019, this was the final curtain call for the PHP 5.6 branch, a version that had powered the web for years but was now officially unsupported and "End of Life".
For a long time, Old Faithful felt secure. After all, 5.6.40 was a "security release." It had been patched to fix multiple vulnerabilities that plagued earlier 5.6.x versions, including integer underflow, buffer overflows, and out-of-bounds read errors. It was the fortress built to withstand the dying days of an era.
But as years passed, the world outside changed. The CVD (Common Vulnerabilities and Exposures) database began to list new shadows:
Memory Corruption: Tiny cracks in how the server handled data, potentially allowing an attacker to crash the system.
Input Validation Flaws: Silent doors left ajar where malicious actors could slip in unauthorized commands.
Denial of Service (DoS): Overwhelming the server until it could no longer serve its users.
The real danger wasn't just in the code itself, but in what it connected to. Old Faithful sat on an unpatched SQL Injection vulnerability (CVE-2026-5640) within its shopping portal software, allowing remote attackers to manipulate database queries and steal customer data. Other critical flaws, like CVE-2023-5640, had reached a "Critical" CVSS score of 9.8, meaning the wall was virtually gone.
The story of 5.6.40 is a warning: staying on unsupported software is no longer an option. To survive in a modern landscape of code injection and cryptographic failures, Old Faithful's administrators finally realized they had to let go of the past and upgrade to a supported version like PHP 8.x.
PHP Vulnerabilities: Assessment, Prevention, and Mitigation - Zend
Version 5.6.40 was released in January 2019, and it has many known security issues because it reached end-of-life on December 31, 2018 (no more security patches).
For those who simply need to know the worst offenders linked to version "5640," here are the top CVEs that remain unpatched in 5.6.40.
Because PHP 5.6.40 has been EOL for years, it has accumulated a backlog of known vulnerabilities that will never be fixed. While PHP 5.6.40 patched issues present in earlier 5.6 versions (like 5.6.30), it is vulnerable to classes of bugs discovered after January 2019. PHP version 5
Common vulnerability types affecting this branch include:
unserialize().The Danger: Since the source code for PHP is open, security researchers and malicious actors know exactly which vulnerabilities exist in 5.6.40. It is a sitting duck.
| Question | Answer | |----------|--------| | Is PHP 5.6.40 safe? | No. Over 200 unpatched vulnerabilities. | | Official CVE link for 5.6.40? | Use CVE Details PHP 5.6 + filter by date > Jan 2019. | | Should I migrate? | Yes, urgently. PHP 5.6 is dead software. |
Last updated: 2026-04-19
Disclaimer: Always verify vulnerabilities against your exact PHP version string using php -v and cross-reference with the NVD database.
PHP version 5.6.40, released in January 2019, was the final security update for the PHP 5.6 branch and is now end-of-life (EOL). While it addressed several critical issues, it remains vulnerable to newer exploits discovered after its support ended. Core Vulnerabilities Addressed in PHP 5.6.40
The 5.6.40 release specifically fixed the following critical security flaws:
Buffer Overflows & Underflows: Fixed multiple heap-based buffer overflows in the mbstring extension (CVE-2019-9023) and an integer underflow in the gd graphics library (CVE-2016-10166).
Out-of-Bounds Reads: Resolved issues in the xmlrpc_decode function (CVE-2019-9020) and the PHAR extension (CVE-2019-9021) that could lead to memory disclosure.
Remote Code Execution (RCE): Addressed flaws that unauthenticated, remote attackers could exploit to compromise systems entirely. Post-Release Risks (EOL Status)
Because PHP 5.6.40 is no longer maintained, it is susceptible to vulnerabilities found in later versions of PHP that were never backported. A major example is CVE-2024-4577, a critical remote code execution flaw in PHP-CGI on Windows that impacts all legacy versions. Security Documentation & Papers
Official ChangeLog: The PHP 5 ChangeLog provides the definitive list of bugs fixed in the 5.6.40 release.
Vulnerability Databases: Detailed technical breakdowns of each CVE associated with this version can be found on CVE Details and Tenable.
Academic/Research Context: For a broader look at PHP security, papers like the USENIX study on SSRF-Defenses in PHP Applications discuss modern attack vectors that still affect legacy environments. PHP 5.6.x < 5.6.40 Multiple vulnerabilities. | Tenable®
The PHP version 5.6.40 has several known vulnerabilities. Here are some resources and guidelines to help you understand and mitigate these issues: Monitor and filter incoming requests : Analyze incoming
This link details what was fixed in the final release. It is useful for showing that 5.6.40 addressed previous issues, but implies nothing after this date was addressed.