SumatraPDF DLL Hijack
Posted on 09 December 2015
Hi @ll, the executable installers [°] of all versions of SumatraPDF (see <http://www.sumatrapdfreader.org/free-pdf-reader-de.html>) are vulnerable: 1. On Windows Embedded POSReady 2009 (alias Windows XP SP3) the installer of the current version 3.1.1 loads and executes a rogue/bogus/malicious DCIMan32.dll ['] eventually found in the directory it is started from (the "application directory"). 2. The installers of older versions of SumatraPDF load and execute a rogue/bogus/malicious UXTheme.dll ['] (and depending on the Windows version others like DCIMan32.dll too) eventually found in the directory they are started from (the "application directory"). For software downloaded with a web browser this is typically the "Downloads" directory: see <https://insights.sei.cmu.edu/cert/2008/09/carpet-bombing-and-directory-poisoning.html>, <http://blog.acrossecurity.com/2012/02/downloads-folder-binary-planting.html> and <http://seclists.org/fulldisclosure/2012/Aug/134> If DCIMan32.dll, UXTheme.dll etc. get(s) planted in the users "Downloads" directory per "drive-by download" this vulnerability becomes a remote code execution. Due to an application manifest embedded in the executable which specifies "requireAdministrator" or the "installer detection" (see <https://technet.microsoft.com/en-us/library/dd835540.aspx#BKMK_InstDet>) of Windows' "user account control" executable installers are typically started with administrative privileges ("protected" administrators are prompted for consent, unprivileged standard users are prompted for an administrator password); execution of DCIMan32.dll then results in an escalation of privilege! Proof of concept/demonstration: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1. visit <http://home.arcor.de/skanthak/sentinel.html>, download <http://home.arcor.de/skanthak/download/SENTINEL.DLL> and save it as DCIMan32.dll in your "Downloads" directory; 2. download <https://kjkpub.s3.amazonaws.com/sumatrapdf/rel/SumatraPDF-3.1.1-install.exe> (via <http://www.sumatrapdfreader.org/free-pdf-reader-de.html>) or <http://software.zeniko.ch/sumatrapdf/SumatraPDF-install.exe> and save it in your "Downloads" directory; 3. execute SumatraPDF-3.1.1-install.exe from your "Downloads" directory; 4. notice the message box displayed from DCIMan32.dll placed in step 1; 5. in your "Downloads" directory copy DCIMan32.dll as UXTheme.dll; 6. download <http://kjkpub.s3.amazonaws.com/sumatrapdf/rel/SumatraPDF-3.0-install.exe> (via <http://www.sumatrapdfreader.org/download-prev-de.html>) and save it in your "Downloads" directory; 7. execute SumatraPDF-3.0-install.exe from your "Downloads" directory; 8. notice the message box displayed from DCIMan32.dll and UXTheme.dll placed in steps 1 and 5. Mitigation(s): ~~~~~~~~~~~~~~ 0. DON'T USE EXECUTABLE INSTALLERS [°]! If your favourite applications are not distributed in the native installer package format of the resp. target platform: ask^WURGE their vendors/developers to provide native installation packages. If they don't: dump these applications, stay away from such cruft! 1. Turn off UAC's privilege elevation for standard users and installer detection for all users: [HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionPoliciesSystem] "ConsentPromptBehaviorUser"=dword:00000000 ; Automatically deny elevation requests "EnableInstallerDetection"=dword:00000000 See <https://technet.microsoft.com/en-us/library/dd835564.aspx#BKMK_RegistryKeys> 2. NEVER execute files in UNSAFE directories (like "Downloads" and and "%TEMP%")! 3. Deny execution (at least) in the "Downloads" directories and all "%TEMP%" directories and their subdirectories: * Add the NTFS ACE "(D;OIIO;WP;;;WD)" meaning "deny execution of files in this directory for everyone, inheritable to all files in all subdirectories" (use CACLS.EXE /S:<SDDL> for example); * Use "software restriction policies" resp. AppLocker. Consider to apply either/both to every "%USERPROFILE%" as well as "%ALLUSERSPROFILE%" alias %ProgramData%" and "%PUBLIC%": Windows doesn't place executables in these directories and beyond. See <http://home.arcor.de/skanthak/safer.html> as well as <http://mechbgon.com/srp/> plus <http://csrc.nist.gov/itsec/SP800-68r1.pdf>, <https://www.nsa.gov/ia/_files/os/win2k/application_whitelisting_using_srp.pdf> or <https://books.google.de/books?isbn=1437914926> and finally <http://www.asd.gov.au/infosec/top35mitigationstrategies.htm>! stay tuned Stefan Kanthak PS: see <http://seclists.org/fulldisclosure/2015/Nov/101> (resp. the not yet finished <http://home.arcor.de/skanthak/!execute.html>) for more details! PPS: the case numbers are not in chronological order. [°] Self-extracting archives and executable installers are flawed^W b(rainde)ad in concept and dangerous in practice. DON'T USE SUCH CRUFT! ALWAYS use the resp. target platforms native package and archive format. For Windows these are .INF (plus .CAB) and .MSI (plus .CAB), introduced 20 years ago (with Windows 95 and Windows NT4) resp. 16 years ago (with Office 2000). Both .INF and .MSI are "opened" by programs residing in %SystemRoot%System32 which are therefore immune to this kind of "DLL and EXE Search Order Hijacking" attack. Since both .INF and .MSI access the contents of .CAB directly they eliminate the attack vector "unsafe temporary directory" too. ['] A well-known (trivial, easy to exploit and easy to avoid) and well-documented vulnerability: see <https://capec.mitre.org/data/definitions/471.html>, <https://technet.microsoft.com/en-us/library/2269637.aspx>, <https://msdn.microsoft.com/en-us/library/ff919712.aspx> and <https://msdn.microsoft.com/en-us/library/ms682586.aspx> Timeline: ~~~~~~~~~ 2015-11-18 vulnerability report sent to authors NO ANSWER, not even an acknowledgement of receipt 2015-11-29 vulnerability report resent to authors 2015-11-29 response from author: "we don't load dciman32.dll in our code. [...] Either way, there's no bug in Sumatra" 2015-11-29 on Windows XP DCIMan32.dll is loaded due to the use of GDI32.dll. This is unique behaviour, not seen in any other executable installer I know. NO ANSWER, not even an acknowledgement of receipt 2015-12-07 report published