php -- bypassing safe_mode, CRLF injection

2002-09-18T00:00:00
ID DSA-168
Type debian
Reporter Debian
Modified 2002-09-18T00:00:00

Description

Wojciech Purczynski found out that it is possible for scripts to pass arbitrary text to sendmail as commandline extension when sending a mail through PHP even when safe_mode is turned on. Passing 5th argument should be disabled if PHP is configured in safe_mode, which is the case for newer PHP versions and for the versions below. This does not affect PHP3, though.

Wojciech Purczynski also found out that arbitrary ASCII control characters may be injected into string arguments of the mail() function. If mail() arguments are taken from user's input it may give the user ability to alter message content including mail headers.

Ulf Härnhammar discovered that file() and fopen() are vulnerable to CRLF injection. An attacker could use it to escape certain restrictions and add arbitrary text to alleged HTTP requests that are passed through.

However this only happens if something is passed to these functions which is neither a valid file name nor a valid url. Any string that contains control chars cannot be a valid url. Before you pass a string that should be a url to any function you must use urlencode() to encode it.

Three problems have been identified in PHP:

  1. The mail() function can allow arbitrary email headers to be specified if a recipient address or subject contains CR/LF characters.
  2. The mail() function does not properly disable the passing of arbitrary command-line options to sendmail when running in Safe Mode.
  3. The fopen() function, when retrieving a URL, can allow manipulation of the request for the resource through a URL containing CR/LF characters. For example, headers could be added to an HTTP request.

These problems have been fixed in version 3.0.18-23.1woody1 for PHP3 and 4.1.2-5 for PHP4 for the current stable distribution (woody), in version 3.0.18-0potato1.2 for PHP3 and 4.0.3pl1-0potato4 for PHP4 in the old stable distribution (potato) and in version 3.0.18-23.2 for PHP3 and 4.2.3-3 for PHP4 for the unstable distribution (sid).

We recommend that you upgrade your PHP packages.