Rufus 3.0 / 3.1 Privilege Escalation

2018.08.07
Risk: Medium
Local: No
Remote: Yes
CVE: N/A
CWE: CWE-264

Hi @ll, like their predecessors, the recently (2018-05-29, 2018-06-19) published versions 3.0 and 3.1 of "Rufus" are riddled with bloody beginners errors, which ALL allow arbitrary code execution WITH escalation of privilege, in MULTIPLE ways. JFTR: to support and ease further attacks, this crap is built without ASLR and without stack cookies/canaries! <https://msdn.microsoft.com/en-us/library/bb430720.aspx> Vulnerability #1 ================ rufus-3.0.exe, rufus-3.0p.exe, rufus-3.1.exe and rufus-3.1p.exe are susceptible to DLL spoofing alias DLL search order hijacking: on a fully patched Windows 7, they load at least the following Windows system DLLs from their "application directory", typically the user's "Downloads" directory %USERPROFILE%\Downloads\, instead from Windows "system directory" %SystemRoot%\System32\, resulting in arbitrary code execution: DWMAPI.dll, UXTheme.dll, Version.dll, CryptSP.dll, NCrypt.dll, BCrypt.dll, RichEd20.dll, DSRole.dll, LogonCli.dll, DFSCli.dll, SAMCli.dll, DSRole.dll For this well-known and well-documented vulnerability see <https://cwe.mitre.org/data/definitions/426.html> and <https://cwe.mitre.org/data/definitions/427.html> plus <https://capec.mitre.org/data/definitions/471.html>. Additionally see Microsoft's developer guidance <https://technet.microsoft.com/en-us/library/2269637.aspx>, <https://msdn.microsoft.com/en-us/library/ff919712.aspx>, <https://msdn.microsoft.com/en-us/library/ms682586.aspx> und <http://blogs.technet.com/b/srd/archive/2014/05/13/load-library-safely.aspx> to avoid this bloody beginner's error. Also see <https://insights.sei.cmu.edu/cert/2008/09/carpet-bombing-and-directory-poisoning.html> and <http://blog.acrossecurity.com/2012/02/downloads-folder-binary-planting.html> plus <https://insights.sei.cmu.edu/cert/2016/06/bypassing-application-whitelisting.html> for "prior art". And last but not least the 20+ year old <http://fy.chalmers.se/~appro/nt/nsaguide.pdf> Since the clueless developer specified "requireAdministrator" in the embedded application manifest, his crap can only be run with administrative privileges, resulting in arbitary code execution WITH escalation of privilege. Demonstration/proof of concept #1: ---------------------------------- 1. Follow the instructions from <https://skanthak.homepage.t-online.de/minesweeper.html> and build a testbed/minefield of 32-bit DLLs in your "Downloads" directory. 2. Download <https://rufus.akeo.ie/downloads/rufus-3.0.exe> and <https://rufus.akeo.ie/downloads/rufus-3.0p.exe> and save them in your "Downloads" directory. 3. Run rufus-3.0.exe and rufus-3.0p.exe: notice the message boxes displayed from multiple DLLs created in step 1! 4. Download <https://rufus.akeo.ie/downloads/rufus-3.1.exe> and <https://rufus.akeo.ie/downloads/rufus-3.1p.exe> and save them in your "Downloads" directory. 5. Run rufus-3.1.exe and rufus-3.1p.exe: notice the message boxes displayed from at least DSROLE.DLL created in step 1! JFTR: if you don't see a message box: open the event log and view the entries from source "Vulnerability and Exploit Detector". Fix: ~~~~ DUMP the executable installer, DUMP the portable crap, provide an .MSI, or a .CAB plus an .INF script. Mitigations: ~~~~~~~~~~~~ See <https://skanthak.homepage.t-online.de/!execute.html> Vulnerability #2 ================ Although running with administrative privileges, this crap extracts files UNPROTECTED [1] into the "current working directory" for later execution (and into the user's %TEMP% directory for later use). For this well-known and well-documented vulnerability see <https://cwe.mitre.org/data/definitions/377.html> and <https://cwe.mitre.org/data/definitions/379.html> plus <https://capec.mitre.org/data/definitions/29.html> An unprivileged user/process running in the same user account [2] can modify the extracted files between their creation and use, and can even create bogus files instead, which this crap then executes. Remember that it runs with administrative rights! Demonstration/proof of concept #2a: ----------------------------------- 1. Open a command prompt, then run the following command lines: MKDIR "%SystemDrive%\CRAPWARE" COPY %COMSPEC% rufus.com ATTRIB.exe +R rufus.com 2. Run the following command line: "%USERPROFILE%\Downloads\rufus-3.1.exe" Notice the string "rufus.com\n" pasted into the command prompt window (really: into the window which happens to have focus) and the copy of the command processor started. 3. Run the following command line: "%USERPROFILE%\Downloads\rufus-3.1p.exe" Again notice the string "rufus.com\n" pasted into the command prompt window, and the subsequent dialog box stating that another instance of this crap is already running. Demonstration/proof of concept #2b: ----------------------------------- 1. Run the following command lines in the still open command prompt: ATTRIB.exe -R rufus.com ERASE rufus.com SET NoDefaultCurrentDirectoryInExePath=* 2. Run the command lines "%USERPROFILE%\Downloads\rufus-3.1.exe" "%USERPROFILE%\Downloads\rufus-3.1p.exe" 3. Notice the error messages | "rufus.com" is not recognized as an internal or external command, | operable program or batch file. from the command prompt, and the complete failure of this crap. Demonstration/proof of concept #2c: ----------------------------------- 1. Add the NTFS ACE "(D;OIIO;WP;;;WD)" meaning "deny execution of files in this directory for everyone, inheritable to files in subdirectories" to the current working directory %SystemDrive%\CRAPWARE. 2. Run the vulnerable applications: notice their complete failure, they neither display their window nor any error message! 3. View the access rights of the file "rufus.com" created in the CWD. stay tuned, and FAR AWAY from such vulnerable and defective crap Stefan Kanthak [1] on Windows, every developer past absolute beginner uses the fourth argument of CreateFile() <https://msdn.microsoft.com/en-us/library/aa363858.aspx> or the second argument of CreateDirectory() <https://msdn.microsoft.com/en-us/library/aa363855.aspx> to specify a "security descriptor" with the desired and needed access rights, at least and especially when running privileged. [2] the ONE and ONLY user account created during Windows setup is an administrator account, and it is used by the vast majority of Windows users for their everyday work: according to Microsoft's own telemetry data, as published in their "Security Intelligence Reports" <https://www.microsoft.com/security/sir/default.aspx> about 1/2 to 3/4 of all (some 600 million) Windows installations report only one active user account.


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