: PHP 5.6.40 lacks the massive engine optimization, abstract syntax tree implementation, and memory efficiency introduced in PHP 7.x and PHP 8.x. Key Vulnerabilities Associated with PHP 5.6.40
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Regular expression functions in the mbstring component were found to have vulnerabilities that could lead to a complete system compromise through crafted multibyte sequences.
, meaning version 5.6.40 and all prior 5.6.x versions no longer receive official patches for newly discovered flaws. Critical Vulnerabilities in PHP 5.6.40 php version 5640 vulnerabilities link
https://nvd.nist.gov/vuln/search/results?form_type=Basic&results_type=overview&query=PHP+5.6.40&search_type=all
Users running versions prior to 5.6.40 are affected by several critical vulnerabilities that this specific release was designed to patch:
: By uploading a specifically crafted image or file file, an attacker can corrupt the heap memory, causing the server process to crash (Denial of Service) or execute shellcode with the privileges of the web server daemon ( www-data or apache ). 3. OpenSSL Dependency Vulnerabilities : PHP 5
The PHAR (PHP Archive) reading functions suffer from validation limits within phar_detect_phar_fname_ext . When a web application parses a maliciously named file via a phar:// stream handler, it allows out-of-bounds reads. Threat actors leverage this to access unallocated system memory regions or read protected system files. 4. XMLRPC Request Exposure (CVE-2019-9020 & CVE-2019-9024)
Some Linux enterprise distributions and premium repositories backport critical security fixes to legacy PHP versions independently of the official PHP development team.
Common vulnerability types affecting this branch include: Critical Vulnerabilities in PHP 5
Deploy a WAF (such as ModSecurity, Cloudflare, or AWS WAF) with specific rulesets designed to block PHP object injection, directory traversal, and malicious file uploads targeting legacy PHP applications. Step 4: Strict Configuration Hardening
: The PHP 5 ChangeLog provides the definitive list of bugs fixed in the 5.6.40 release.
The PHAR (PHP Archive) component contains a use-after-free vulnerability during directory processing. Attackers utilizing malicious .phar files can corrupt system memory to bypass security controls.
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If you are currently running PHP 5.6.40, I can help you find resources to check your or calculate the risks of not upgrading. Let me know what framework (like WordPress) you are using! PHP Object Injection - OWASP Foundation