The zend_string_extend function in Zend/zend_string.h in PHP through 7.1.5 does not prevent changes to string objects that result in a negative length, which allows remote attackers to cause a denial of service (application crash) or possibly have unspecified other impact by leveraging a script's use of .= with a long string.

The GNU Multiple Precision Arithmetic Library (GMP) interfaces for PHP through 7.1.4 allow attackers to cause a denial of service (memory consumption and application crash) via operations on long strings. NOTE: the vendor disputes this, stating "There is no security issue here, because GMP safely aborts in case of an OOM condition. The only attack vector here is denial of service. However, if you allow attacker-controlled, unbounded allocations you have a DoS vector regardless of GMP's OOM behavior.

PHP through 7.1.11 enables potential SSRF in applications that accept an fsockopen or pfsockopen hostname argument with an expectation that the port number is constrained. Because a :port syntax is recognized, fsockopen will use the port number that is specified in the hostname argument, instead of the port number in the second argument of the function.

ext/libxml/libxml.c in PHP before 5.5.22 and 5.6.x before 5.6.6, when PHP-FPM is used, does not isolate each thread from libxml_disable_entity_loader changes in other threads, which allows remote attackers to conduct XML External Entity (XXE) and XML Entity Expansion (XEE) attacks via a crafted XML document, a related issue to CVE-2015-5161.

The pcre_compile2 function in pcre_compile.c in PCRE 8.38 mishandles the /((?:F?+(?:^(?(R)a+\"){99}-))(?J)(?'R'(?'R'<((?'RR'(?'R'\){97)?J)?J)(?'R'(?'R'\){99|(:(?|(?'R')(\k'R')|((?'R')))H'R'R)(H'R))))))/ pattern and related patterns with named subgroups, which allows remote attackers to cause a denial of service (heap-based buffer overflow) or possibly have unspecified other impact via a crafted regular expression, as demonstrated by a JavaScript RegExp object encountered by Konqueror.