Abusing Adobe Reader’s JavaScript APIs by Abdul-Aziz Hariri & Brian Gorenc - CODE BLUE 2015
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The document discusses the exploitation of Adobe Reader's JavaScript APIs to gain remote code execution. It details the process of vulnerability discovery and constructing exploits, emphasizing the importance of understanding attack surfaces and leveraging undocumented APIs. The authors aim to illustrate how property overloading and privilege escalation can be utilized to execute malicious code without relying on memory corruption techniques.
Abusing Adobe Reader’s JavaScript APIs by Abdul-Aziz Hariri & Brian Gorenc - CODE BLUE 2015
- 1. Abusing Adobe Reader’s JavaScript APIs Brian Gorenc, Manager, Vulnerability Research AbdulAziz Hariri, Security Researcher
- 2. Agenda • Introduction • Understanding the Attack Surface • Vulnerability Discovery • Constructing the Exploit
- 3. Introduction
- 4. Introduction 4 HP Zero Day Initiative AbdulAziz Hariri - @abdhariri Security Researcher at the Zero Day Initiative Root cause analysis, vulnerability discovery, and exploit development Brian Gorenc - @maliciousinput Head of Zero Day Initiative Organizer of Pwn2Own Hacking Competitions
- 5. Internal research starting in December 2014 Bug Hunters Patched Vulnerabilities CVE-2015-5085, CVE-2015-5086, CVE-2015- 5090, CVE-2015-5091, CVE-2015-4438, CVE- 2015-4447, CVE-2015-4452, CVE-2015-5093, CVE-2015-5094, CVE-2015-5095, CVE-2015- 5101, CVE-2015-5102, CVE-2015-5103, CVE- 2015-5104, CVE-2015-5113, CVE-2015-5114, CVE-2015-5115, CVE-2015-5100, CVE-2015- 5111, CVE-2015-4435, CVE-2015-4441, CVE- 2015-4445, CVE-2015-3053, CVE-2015-3055, CVE-2015-3057, CVE-2015-3058, CVE-2015- 3065, CVE-2015-3066, CVE-2015-3067, CVE- 2015-3068, CVE-2015-3071, CVE-2015-3072, CVE-2015-3073, CVE-2015-3054, CVE-2015- 3056, CVE-2015-3061, CVE-2015-3063, CVE- 2015-3064, CVE-2015-3069, CVE-2015-3060, CVE-2015-3062 Unpatched Vulnerabilities ZDI-CAN-3058, ZDI-CAN-3059, ZDI-CAN- 3060, ZDI-CAN-3061, ZDI-CAN-3062, ZDI- CAN-3063, ZDI-CAN-3065, ZDI-CAN-3066, ZDI-CAN-3067, ZDI-CAN-3079, ZDI-CAN- 3081, ZDI-CAN-3083, ZDI-CAN-3085, ZDI- CAN-3086, ZDI-CAN-3087, ZDI-CAN-3088, ZDI-CAN-3089, ZDI-CAN-3090, ZDI-CAN- 3091, ZDI-CAN-3068, ZDI-CAN-3069, ZDI- CAN-3070, ZDI-CAN-3073, ZDI-CAN-3074, ZDI-CAN-3080, ZDI-CAN-3082, ZDI-CAN- 3084, ZDI-CAN-3103, ZDI-CAN-3111, ZDI- CAN-3051, ZDI-CAN-3050, ZDI-CAN-3049, ZDI-CAN-3048, ZDI-CAN-3047, ZDI-CAN- 3046, ZDI-CAN-3043, ZDI-CAN-3036, ZDI- CAN-3022, ZDI-CAN-3021, ZDI-CAN-2019, ZDI-CAN-3018, ZDI-CAN-3017, ZDI-CAN- 3016, ZDI-CAN-3015, ZDI-CAN-2998, ZDI- CAN-2997, ZDI-CAN-2958, ZDI-CAN-2816, ZDI-CAN-2892, ZDI-CAN-2893 …more to come. 5
- 7. Understanding Attack Surface 7 Prior research and resources • The life of an Adobe Reader JavaScript bug (CVE-2014-0521) - Gábor Molnár • First to highlight the JS API bypass issue • The bug was patched in APSB14-15 and was assigned CVE-2014-0521 • According to Adobe, this could lead to information disclosure • https://molnarg.github.io/cve-2014-0521/#/ • Why Bother Assessing Popular Software? – MWR Labs • Highlights various attack vectors on Adobe reader • https://labs.mwrinfosecurity.com/system/assets/979/original/Why_bother_assessing_p opular_software.pdf
- 8. Understanding Attack Surface 8 ZDI Research Stats • Primary Adobe research started internally in December 2014 • We were not getting many cases in Reader/Acrobat • Main goal was to kill as much bugs as possible • Internal discoveries varied in bug type – JavaScript API Restriction Bypasses – Memory Leaks – Use-After-Frees – Elevation of Privileges – etc.
- 9. Understanding Attack Surface 9 Insights Into Reader’s JavaScript API’s • Adobe Acrobat/Reader exposes a rich JS API • JavaScript API documentation is available on the Adobe website • A lot can be done through the JavaScript API (Forms, Annotations, Collaboration etc..) • Mitigations exist for the JavaScript APIs • Some API’s defined in the documentation are only available in Acrobat Pro/Acrobat standard • Basically JavaScript API’s are executed in two contexts: – Privileged Context – Non-Privileged Context
- 10. Understanding Attack Surface 10 Insights Into Reader’s JavaScript API’s • Privileged vs Non-Privileged contexts are defined in the JS API documentation: • A lot of API’s are privileged and cannot be executed from non-privileged contexts:
- 11. Understanding Attack Surface 11 Insights Into Reader’s JavaScript API’s • Privileged API’s warning example from a non-privileged context:
- 12. Trusted Functions 12 Executing privileged methods in a non-privileged context
- 13. Understanding Attack Surface 13 Folder-Level Scripts • Scripts stored in the JavaScript folder inside the Acrobat/Reader folder • Used to implement functions for automation purposes • Contains Trusted functions that execute privileged API’s • By default Acrobat/Reader ships with JSByteCodeWin.bin • JSByteCodeWin.bin is loaded when Acrobat/Reader starts up • It’s loaded inside Root, and exposed to the Doc when a document is open
- 14. Understanding Attack Surface 14 Decompiling • JSByteCodeWin.bin is compiled into SpiderMoney 1.8 XDR bytecode • JSByteCodeWin.bin contains interesting Trusted functions • Molnarg was kind enough to publish a decompiler for SpiderMonkey – https://github.com/molnarg/dead0007 – Usage: ./dead0007 JSByteCodeWin.bin > output.js – Output needs to be prettified – ~27,000 lines of Javascript
- 16. Vulnerability Discovery 16 JavaScript Implicit Method Calls
- 17. Vulnerability Discovery 17 JavaScript Method/Property Overloading • __defineGetter__ and __defineSetter__
- 18. Vulnerability Discovery 18 JavaScript Method/Property Overloading • __proto__
- 19. Vulnerability Discovery 19 Code Auditing for Overloading Opportunities • Search for ‘eval’
- 20. Vulnerability Discovery 20 Code Auditing for Overloading Opportunities • Search for ‘app.beginPriv(“
- 21. Vulnerability Discovery 21 Achieving System-Level eval() • Overload property access with a custom function
- 22. Vulnerability Discovery 22 Executing Privileged APIs • Replace a property with a privileged function
- 23. Vulnerability Discovery 23 Vulnerability Chaining • Set up the system-level eval such that it executes the bulk of the payload • Create the replacement attribute such that it now calls a privileged API • Trigger the call
- 24. Vulnerability Discovery 24 Proof of Concept – CVE-2015-3073
- 27. Vulnerability Discovery 27 Adobe Reader 11.0.10 – Before Patch
- 28. Vulnerability Discovery 28 Adobe Reader DC – After Patch
- 29. Vulnerability Discovery 29 Recap • To achieve a JavaScript bypass we need to • Achieve execution within the system context • Escalate privileges by overriding an object method – Must be in a privileged block within a trusted function
- 31. Constructing the exploit 31 Overview • Research triggered from https://helpx.adobe.com/security/products/reader/apsb14-15.html: • Challenge: Gain Remote Code Execution through the bypass issue • We might be able to do that through the JS API’s that we know about
- 32. Constructing the exploit 32 Because documentation sucks.. • We needed to find a way to dump a file on disk • The file can be of any type (try to avoid restrictions) • Let’s have a look at the Collab object…through the JS API from Adobe:
- 33. Constructing the exploit 33 “If you want to keep a secret, you must also hide it from yourself.” – G. Orwell • From all the 128 undocumented methods, the Collab.uri* family is specifically interesting:
- 34. Constructing the exploit 34 “The more you leave out, the more you highlight what you leave in.” - H. Green • Too good to be true, so I consulted uncle Google before digging more:
- 35. Constructing the exploit 35 Show me what you got... • Quick overview of the interesting methods:
- 36. Constructing the exploit 36 • Overview of the Collab.uri* API’s: – The API’s are used for “Collaboration” – uriDeleteFolder/uriDeleteFile/uriPutData/uriCreateFolder are privileged API’s – uriEnumerateFiles is NOT privileged – The Collab.uri* methods take a URI path as an argument (at least) – The path expected should be a UNC path – The UNC path should start with smb:// or file:// • The API’s fail to: – Sanitize the UNC path (smb://localhost/C$/XXX works) – Check the filetype of the filename to be written on disk (in the case of uriPutData) – Check the content of oData object to be dumped (in the case of uriPutData)
- 37. Constructing the exploit 37 • What we have so far: – We can dump files on disk using the Collab.uriPutData() method – The file contents that we want to dump should be passed as an oData object – Stream objects do work!
- 38. Constructing the exploit 38 – We can attach files in PDF documents and extract the contents – We should chain the uriPutData call with one of the bypasses that we discussed earlier Then what ? How can we get RCE? Actually there are two obvious ways...
- 39. Constructing the exploit 39 Gaining RCE • First way…a la Chaouki: Basically write a file to the startup and wait for a logoff/logon • Second way is writing a DLL that would be loaded by Adobe Acrobat
- 40. Vulnerable Versions 40 Product Windows MacOSX Adobe Reader Vulnerable – Limited (Sandbox) Vulnerable Adobe Reader DC Vulnerable – Limited (Sandbox) Vulnerable Adobe Acrobat Pro Vulnerable Vulnerable Adobe Acrobat Pro DC Vulnerable Vulnerable
- 41. Constructing the exploit 41 Putting it all together (Adobe Acrobat Pro) 1. Attach our payload to the PDF 2. Create a JS that would execute when the document is open 3. JS is composed of: 1. Extraction of the attachment 2. Bypass JS privileges 3. Execute Collab.uriPutData to output our payload (startup/dll) Extract Attachment Bypass JS Privileges Call uriPutData with the extracted attachment RCE
- 43. Reader for MacOSX DEMO 43
- 44. Conclusion
- 45. Recap 45 Abusing Adobe Reader’s JavaScript APIs • Goal – Leverage JavaScript APIs to gain remote code execution on Adobe Reader/Acrobat – No memory corruption • Plan of Attack 1. Obtain an arbitrary eval() by JavaScript property overloading and redefinition 2. Chain eval() with privilege escalation through app.trustedFunction 3. Leverage undocumented APIs to execute malicious code 4. Profit?
- 46. Thank you