Multiple Vendor xpdf JPX Stream Reader Heap Overflow Vulnerability iDefense Security Advisory 12.05.05 www.idefense.com/application/poi/display?id=345&type=vulnerabilities December 5, 2005 I. BACKGROUND Xpdf is an open-source viewer for Portable Document Format (PDF) files. II. DESCRIPTION Local exploitation of a heap-based buffer overflow vulnerability in xpdf, as included by multiple vendor's software distributions, could allow attackers to cause a denial of service (DoS) condition, potentially resulting in arbitrary code execution. The vulnerability specifically exists due to insufficient input validation in the JPX Stream parsing code for decoding embedded JPEG 2000 images. The JPXStream::readCodestream function from xpdf/JPXStream.cc takes the value of nXTiles and nYTiles from user- controllable data from within the PDF file. The nXTiles and nYTiles values are then used in a gmallocn() call as shown below. GBool JPXStream::readCodestream(Guint len) { ... switch (segType) { case 0x4f: // SOC - start of codestream // marker only break; case 0x51: // SIZ - image and tile size if (!readUWord(&capabilities) || !readULong(&img.xSize) || !readULong(&img.ySize) || !readULong(&img.xOffset) || !readULong(&img.yOffset) || !readULong(&img.xTileSize) || !readULong(&img.yTileSize) || !readULong(&img.xTileOffset) || !readULong(&img.yTileOffset) || !readUWord(&img.nComps)) { error(getPos(), "Error in JPX SIZ marker segment"); return gFalse; } ... img.nXTiles = (img.xSize - img.xTileOffset + img.xTileSize - 1) / img.xTileSize; img.nYTiles = (img.ySize - img.yTileOffset + img.yTileSize - 1) / img.yTileSize; img.tiles = (JPXTile *)gmallocn(img.nXTiles * img.nYTiles, sizeof(JPXTile)); The values are used again later in JPEG format parsing code to copy data from the file into a pre-allocated buffer in the heap. Overly large values supplied to nXTiles and nYTiles result in corruption of heap memory, which results in a DoS condition. This could result in arbitrary code execution. III. ANALYSIS Exploitation could result in arbitrary code execution with privileges of the xpdf process. Currently, exploitation resulting in code execution is theoretical and dependant on the process memory layout. A typical exploitation attempt would require an attacker to supply a malicious pdf to the victim. The victim would need to open the corrupt pdf file in xpdf. Only then would the vulnerability be triggered. IV. DETECTION iDefense has confirmed the existence of this vulnerability in xpdf 3.01. All earlier versions of xpdf are suspected vulnerable. The following vendors include susceptible xpdf packages within their operating system distributions: . The Debian Project: Linux 3.0 and 3.1 V. WORKAROUND iDefense is currently unaware of any effective workarounds for this vulnerability. VI. VENDOR RESPONSE A patch for this vulnerability is available at: ftp://ftp.foolabs.com/pub/xpdf/xpdf-3.01pl1.patch Updated binaries (version 3.01pl1) are available at: http://www.foolabs.com/xpdf/download.html VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the name CAN-2005-3193 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 10/13/2005 Initial vendor notification 10/19/2005 Initial vendor response 12/05/2005 Coordinated public disclosure IX. CREDIT iDefense credits infamous41md (at) hotpop (dot) com [email concealed] with the discovery of this vulnerability. Get paid for vulnerability research http://www.iDefense.com/poi/teams/vcp.jsp Free tools, research and upcoming events http://labs.iDefense.com X. LEGAL NOTICES Copyright C 2005 iDefense, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDefense. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please email customerservice (at) iDefense (dot) com [email concealed] for permission. 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.