An information leak vulnerability exists in PHP. An integer overflow which occurs while performing sanity checks on the input parameters to the substr_compare() function makes it possible to compare offsets outside of the allocated buffer. This allows memory access outside the buffer and the retrieval of sensitive information, leading to a loss of confidentiality.

substr_compare() performs two sanity checks on the input parameters:

Sanity Check #1 - ensures that a negative offset is considered relative to the end of the first input string
if (offset < 0) {
offset = s1_len + offset;
offset = (offset < 0) ? 0 : offset;
}

Sanity Check #2 - ensures that offset and requested length do not exceed the buffer length, but does not take into account that the addition of two positive signed variables can result in a negative value when an integer overflow occurs
if ((offset + len) > s1_len) {
php_error_docref(NULL TSRMLS_CC, E_WARNING, "The start position cannot exceed ...");
RETURN_FALSE;
}

Comparing an ASCIIZ char and a ASCII 01 char with an offset outside the buffer and comparing the return values of substr_compare() it is possible to determine ASCII value of the byte outside the buffer.

Upgrade to version 5.2.2 or higher, as it has been reported to fix this vulnerability. An upgrade is required as there are no known workarounds.

• CVE ID: 2007-1375 (see also: NVD)
• Bugtraq ID: 22851
• Secunia Advisory ID: 24606 24606 25057 25062 26895
• Milw0rm: 3424
• Exploit Database: 3424
• Other Advisory URL: http://www.gentoo.org/security/en/glsa/glsa-200703-21.xml
  http://www.mandriva.com/security/advisories?name=MDKSA-2007:187
  http://www.php-security.org/MOPB/MOPB-14-2007.html
  http://www.ubuntu.com/usn/usn-455-1
  http://www.us.debian.org/security/2007/dsa-1283
• Generic Exploit URL: http://www.php-security.org/MOPB/code/MOPB-14-2007.php
• Vendor URL: http://www.php.net/
• Vendor Specific News/Changelog Entry: http://www.php.net/ChangeLog-5.php

• Stefan Esser - sesserhardened-php.net - www.hardened-php.net