sapi/fpm/fpm/fpm_log.c in PHP before 5.5.31, 5.6.x before 5.6.17, and 7.x before 7.0.2 misinterprets the semantics of the snprintf return value, which allows attackers to obtain sensitive information from process memory or cause a denial of service (out-of-bounds read and buffer overflow) via a long string, as demonstrated by a long URI in a configuration with custom REQUEST_URI logging.
https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05240731
http://www.search-lab.hu/about-us/news/111-some-unusual-vulnerabilities-in-the-php-engine
http://www.openwall.com/lists/oss-security/2016/05/29/1
http://rhn.redhat.com/errata/RHSA-2016-2750.html
http://php.net/ChangeLog-7.php
http://php.net/ChangeLog-5.php
http://github.com/php/php-src/commit/2721a0148649e07ed74468f097a28899741eb58f?w=1