PHP could be made to denial of service, expose sensitive information or execute arbitrary code if it received a specially crafted regular expression.

=========================================================================Ubuntu Security Notice USN-4088-1
August 07, 2019

php5 vulnerability
=========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 14.04 ESM
- Ubuntu 12.04 ESM

Summary:

PHP could be made to denial of service, expose sensitive information
or execute arbitrary code if it received a specially crafted regular
expression.

Software Description:
- php5: HTML-embedded scripting language interpreter

Details:

It was discovered that PHP incorrectly handled certain regular expressions.
An attacker could possibly use this issue to expose sensitive information,
cause a denial of service or execute arbitrary code.

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 14.04 ESM:
  libapache2-mod-php5             5.5.9+dfsg-1ubuntu4.29+esm4
  php5-cgi                        5.5.9+dfsg-1ubuntu4.29+esm4
  php5-cli                        5.5.9+dfsg-1ubuntu4.29+esm4
  php5-fpm                        5.5.9+dfsg-1ubuntu4.29+esm4
  php5-xmlrpc                     5.5.9+dfsg-1ubuntu4.29+esm4

Ubuntu 12.04 ESM:
  libapache2-mod-php5             5.3.10-1ubuntu3.38
  php5-cgi                        5.3.10-1ubuntu3.38
  php5-cli                        5.3.10-1ubuntu3.38
  php5-fpm                        5.3.10-1ubuntu3.38
  php5-xmlrpc                     5.3.10-1ubuntu3.38

In general, a standard system update will make all the necessary changes.

References:
  https://ubuntu.com/security/notices/USN-4088-1
  CVE-2019-13224