The SOAP HTTP client guards its response buffer growth with a check that relies on signed integer overflow, which is undefined behaviour and is not guaranteed to trigger. When the check is optimised away, a malicious SOAP server can make the client allocate a buffer far smaller than the data it then writes into it, producing a heap buffer overflow.
{
"cpes": [
"cpe:2.3:a:php:php:*:*:*:*:*:*:*:*"
],
"severity": "Medium"
}