You can use this for an internal security report, a system admin log, or a client advisory.

A SQL injection vulnerability exists in PHP 5.6.40 due to improper sanitization of user input in the mysqli extension. An attacker can exploit this vulnerability to inject malicious SQL code, potentially leading to data breaches or unauthorized data modifications.

A "Use After Free" vulnerability where invalid input to xmlrpc_decode() could cause memory corruption or information disclosure.

Outdated versions are highly susceptible to RCE through unpatched bugs in core functions or extensions like Unpatched Dependency Chains:

Here is an interesting guide structured not as a dry list of CVEs, but as a for developers forced to maintain legacy systems.

Stealing database credentials, configuration files, and customer data. Denial of Service (DoS): Crashing the PHP service. 2. Why PHP 5.6.40 is Insecure in 2026

4. FPM (FastCGI Process Manager) Vulnerabilities (CVE-2019-11043) Env Var Injection / Buffer Underflow Impact: Critical

Several core extensions inside PHP 5.6.40 contain confirmed memory validation errors: PHP 5.6: Why you should upgrade - Influential Software

The mbstring extension contains multiple heap-based buffer overflows within its regular expression functions, such as fetch_token and compile_string_node . An unauthenticated, remote attacker can exploit these by sending a specially crafted regular expression containing multibyte sequences. This can cause memory corruption and potentially lead to a .

: Heap out-of-bounds read and read-after-free states caused by improper validation of raw XML input data. CVE-2019-9021 PHAR extension