[ASA-201910-14] php: arbitrary code execution

[Remi Gacogne]

Arch Linux Security Advisory ASA-201910-14
==========================================

Severity: Critical
Date    : 2019-10-25
CVE-ID  : CVE-2019-11043
Package : php
Type    : arbitrary code execution
Remote  : Yes
Link    : https://security.archlinux.org/AVG-1052

Summary
=======

The package php before version 7.3.11-1 is vulnerable to arbitrary code
execution.

Resolution
==========

Upgrade to 7.3.11-1.

# pacman -Syu "php>=7.3.11-1"

The problem has been fixed upstream in version 7.3.11.

Workaround
==========

If nginx and php-fpm share the same filesystem, one can first check the
script actually exists, so the malicious request will never make it to
php-fpm (it is usually done using something like `try_files $uri
=404`). Or there may be cgi.fix_pathinfo=0 which will also prevent
exploitation.

Description
===========

A buffer underflow issue has been found in the php-fpm component of php
before 7.3.11, 7.2.24 and 7.1.33, leading to remote code execution in
certain nginx + php-fpm configurations. This vulnerability can be
exploited if the fastcgi_split_path_info directive contains a regexp
that can be broken by an attacker by supplying %0a in the path info
which results in the fastcgi_param PATH_INFO being empty.

Impact
======

A remote attacker is able to execute arbitrary code on the affected
host by supplying %0a in the path info if php-fpm is used with a
vulnerable nginx configuration.

References
==========

https://bugs.php.net/bug.php?id=78599
https://git.php.net/?p=php-src.git;a=commitdiff;h=19e17d3807e6cc0b1ba9443ec5facbd33a61f8fe
https://github.com/neex/phuip-fpizdam
https://security.archlinux.org/CVE-2019-11043

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