Multiple Vendor OpenOffice rtl_allocateMemory() Integer Overflow Vulnerability

I. BACKGROUND

OpenOffice is an open-source desktop office suite for many of today's popular operating systems. For more information, see the vendor's site found at the following URL.

http://www.openoffice.org/

II. DESCRIPTION

Remote exploitation of an integer overflow vulnerability in OpenOffice, as included in various vendors' operating system distributions, allows attackers to execute arbitrary code with the privileges of the logged-in user.

The vulnerability exists due to the rtl_allocateMemory() function rounding up allocation requests to be aligned on an 8 byte boundary without checking if this rounding results in an integer overflow condition. The vulnerable code is as follows, taken from sal/rtl/source/alloc_global.c:

   191  void *
   192  SAL_CALL rtl_allocateMemory (sal_Size n)
   193  {
   194          void * p = 0;
   195          if (n > 0)
   196          {
   197                  char *     addr;
   198                  sal_Size   size = RTL_MEMORY_ALIGN(n + RTL_MEMALIGN, RTL_MEMALIGN);
   199
   200                  int index = (size - 1) >> RTL_MEMALIGN_SHIFT;
   201                  OSL_ASSERT(RTL_MEMALIGN >= sizeof(sal_Size));
   202
   203  try_alloc:
   204                  if (index < RTL_MEMORY_CACHED_LIMIT >> RTL_MEMALIGN_SHIFT)
   205                          addr = (char*)rtl_cache_alloc(g_alloc_table[index]);
   206                  else
   207                          addr = (char*)rtl_arena_alloc (gp_alloc_arena, &size);
   208

The problem occurs at line 198. The n + RTL_MEMALIGN calculation can overflow if n > UINT_MAX - RTL_MEMALIGN. This results in an undersized buffer being allocated at try_alloc. This buffer is then passed back to the calling function, which assumes that the buffer is much larger than it actually is. This results in a heap overflow.

As this vulnerability occurs in the core memory allocator, there are numerous ways to trigger the vulnerable code using a wide variety of different file types.

III. ANALYSIS

Exploitation of this vulnerability results in the execution of arbitrary code with the privileges of the user opening the file. To exploit this vulnerability, an attacker needs to convince a user to open a malicious file. After opening the file, no further interaction is needed.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in OpenOffice version 2.4. Previous versions may also be affected.

V. WORKAROUND

iDefense is currently unaware of any workarounds for this issue. Since the vulnerability can be triggered by so many different file types, disabling access to certain file types is not a valid workaround. As such, avoid opening files from untrusted parties and unexpected files from trusted parties.

VI. VENDOR RESPONSE

OpenOffice.Org has addressed this vulnerability by releasing version 2.4.1 of their product. For more information, consult the OOo Security Bulletin at the following URL.

http://www.openoffice.org/security/cves/CVE-2008-2152.html

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2008-2152 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org/), which standardizes names for security problems.

VIII. DISCLOSURE TIMELINE

05/08/2008 Initial vendor notification 05/09/2008 Initial vendor response 06/10/2008 Coordinated public disclosure

IX. CREDIT

This vulnerability was discovered by Sean Larsson, iDefense Labs.

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X. LEGAL NOTICES

Copyright © 2008 iDefense, Inc.

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Disclaimer: The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information.