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Date: Tue, 14 Aug 2012 00:03:18 -0600
From: Kurt Seifried <kseifried@...hat.com>
To: oss-security@...ts.openwall.com
CC: "Jason A. Donenfeld" <Jason@...c4.com>
Subject: Re: Tunnel Blick: Multiple Vulnerabilities to Local
Root and DoS (OS X)
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On 08/13/2012 06:34 AM, Jason A. Donenfeld wrote:
> Hi Kurt,
>
> Sure, I'll trace each one, and include line numbers with the code.
> This code comes from:
> http://code.google.com/p/tunnelblick/source/browse/trunk/tunnelblick/openvpnstart.m?r=2095
Thanks,
>
without the details this would have been impossible, as it is
I'm going to break one CVE editorial rule, but I think it's for a good
reason (but I could also be wrong). So in summary:
==================
1. A race condition in file permissions checking can lead to local
root. - TOCTOU
Please use CVE-2012-3483 for this issue
==================
2. Insufficient checking of merely 0:0 744 can lead to local root on
systems with particular configurations.
Please use CVE-2012-3484 for this issue
==================
3. Insufficient validation of path names can allow for arbitrary
kernel module loading, which can lead to local root.
4. Insufficient validation of path names can allow execution of
arbitrary scripts as root, leading to local root.
5. Insufficient path validation in errorExitIfAttackViaString can lead
to deletion of files as root, leading to DoS.
Please use CVE-2012-3485 for these issues
==================
6. Allowing OpenVPN to run with user given configurations can lead to
local root.
Please use CVE-2012-3486 for this issue
==================
7. Race condition in process killing. - TOCTOU
Please use CVE-2012-3487 for this issue
although #1 and #7 are both TOCTOU race conditions (and thus should be
merged) one is a classic file perms check/use, the other is quite
different, process listing/killing, so I split the CVE (they are
sufficiently different to warrant it I think).
>
> 1. A race condition in file permissions checking can lead to local
> root. PoC:
> http://git.zx2c4.com/Pwnnel-Blicker/tree/pwnnel-blicker.c
>
> 927 int runScript(NSString * scriptName, 928 int
> argc, 929 char * cfgName, 930
> char * cfgLoc) 931 { * 964 if (
> checkOwnerAndPermissions(scriptPath, 0, 0, @"744") ) { 965 966
> fprintf(stderr, "'%s' executing...\n", [scriptName UTF8String]); *
> 967 returnValue = runAsRoot(scriptPath,
> [NSArray array]); 968 fprintf(stderr, "'%s'
> returned with status %d\n", [scriptName UTF8String], returnValue);
> 969 }
>
> Here, there's a race condition between the two stared lines.
>
>
> 2. Insufficient checking of merely 0:0 744 can lead to local root
> on systems with particular configurations.
>
> 964 if ( checkOwnerAndPermissions(scriptPath, 0,
> 0, @"744") ) { and 801 if ( !
> checkOwnerAndPermissions(preConnectPath, 0, 0, @"744") ) { and 847
> if ( ! checkOwnerAndPermissions(postTunTapPath, 0, 0, @"744") )
> { and 1675 if ( !
> checkOwnerAndPermissions(filePath, 0, 0, @"744") ) { //
> shell scripts are 744
>
> Testing a file for whether or not it's 744 and owned by root:root
> is not sufficient for deciding whether a unprivileged should be
> able to run it as root. This not only makes every 744 root:root
> file on the file system a potential vector, but destroys the nosuid
> mount flag OS X uses for all user mountable images and network
> shares.
>
>
> 3. Insufficient validation of path names can allow for arbitrary
> kernel module loading, which can lead to local root.
>
> 86 execPath = [[NSString stringWithUTF8String:argv[0]]
> stringByDeletingLastPathComponent]; 1355 void loadKexts(unsigned
> int bitMask) 1356 { 1357 if ( ( bitMask &
> (OPENVPNSTART_OUR_TAP_KEXT | OPENVPNSTART_OUR_TUN_KEXT) ) == 0 )
> { 1358 return; 1359 } 1360 1361 NSMutableArray*
> arguments = [NSMutableArray arrayWithCapacity: 2]; 1362 if (
> (bitMask & OPENVPNSTART_OUR_TAP_KEXT) != 0 ) { 1363
> NSString * tapkext = [@"tap" stringByAppendingString:
> TunTapSuffixToUse([execPath stringByAppendingPathComponent:
> @"tap"])]; 1364 [arguments addObject: [execPath
> stringByAppendingPathComponent: tapkext]]; 1365
> fprintf(stderr, "Loading %s\n", [tapkext UTF8String]); 1366 }
> 1367 if ( (bitMask & OPENVPNSTART_OUR_TUN_KEXT) != 0 ) { 1368
> NSString * tunkext = [@"tun" stringByAppendingString:
> TunTapSuffixToUse([execPath stringByAppendingPathComponent:
> @"tun"])]; 1369 [arguments addObject: [execPath
> stringByAppendingPathComponent: tunkext]]; 1370
> fprintf(stderr, "Loading %s\n", [tunkext UTF8String]); 1371 }
> 1372 1373 becomeRoot();
>
> 1374 int status; 1375 int i; 1376 for (i=0; i < 5; i++)
> { 1377 NSTask * task = [[[NSTask alloc] init]
> autorelease]; 1378 1379 [task
> setLaunchPath:@"/sbin/kextload"]; 1380 1381 [task
> setArguments:arguments]; 1382 1383 [task launch];
>
> As you can see, the file name of the kernel extension being loaded
> is derived from argv[0], which can be trivially bypassed (
> execl(..., "/attacker/controlled/argv/zero", ...) ).
>
>
> 4. Insufficient validation of path names can allow execution of
> arbitrary scripts as root, leading to local root. PoC:
> http://git.zx2c4.com/Pwnnel-Blicker/tree/pwnnel-blicker-for-kids.sh
>
> 86 execPath = [[NSString stringWithUTF8String:argv[0]]
> stringByDeletingLastPathComponent]; 919 void
> runOpenVpnToGetVersion(NSString * openvpnVersion) 920 { 921
> NSString * openvpnPath = openvpnToUsePath([execPath
> stringByAppendingPathComponent: @"openvpn"], openvpnVersion); 922
> runAsRoot(openvpnPath, [NSArray arrayWithObject: @"--version"]);
> 923 }
>
> This basically amounts to this being run as root: $(dirname
> argv[0])/openvpn --version.
>
>
>
> 5. Insufficient path validation in errorExitIfAttackViaString can
> lead to deletion of files as root, leading to DoS. 164 }
> else if( strcmp(command, "deleteLogs") == 0 ) { 165 if (argc ==
> 4) { 166 NSString* configFile = [NSString
> stringWithUTF8String:argv[2]]; 167
> errorExitIfAttackViaString(configFile); 168
> unsigned cfgLocCode = atoi(argv[3]); 169
> deleteLogFiles(configFile, cfgLocCode); 170
> syntaxError = FALSE; 171 } 1735 void
> errorExitIfAttackViaString(NSString * string) 1736 { 1737 BOOL
> startsWithDot = [string hasPrefix: @"."]; 1738 NSRange r =
> [string rangeOfString: @"/.."]; 1739 if ( startsWithDot 1740
> || (r.length != 0) ) { 1741 fprintf(stderr, "Tunnelblick
> openvpnstart: Apparent attack detected; string being tested is
> %s\n", [string UTF8String]); 1742 [pool drain]; 1743
> exit(EXIT_FAILURE); 1744 } 1745 }
>
> The "exit if attack string" function doesn't check for links of
> any kind, symbolic or hard, so this validation is not sufficient.
>
>
> 6. Allowing OpenVPN to run with user given configurations can lead
> to local root. 939 if ( [configFile hasSuffix: @"tblk"] )
> { 940 unsigned cfgLocCode = atoi(cfgLoc); 941
> switch (cfgLocCode) { 942 case 0: 943
> configPrefix = [NSHomeDirectory()
> stringByAppendingPathComponent:@"/Library/Application
> Support/Tunnelblick/Configurations"]; 944
> break; 945 case 1: 946
> configPrefix = [NSString stringWithFormat:@"/Library/Application
> Support/Tunnelblick/Users/%@", NSUserName()]; 947
> break; 948 case 2: 949
> configPrefix = [execPath stringByAppendingPathComponent:
> @"Deploy"]; 950 break; 951 case
> 3: 952 configPrefix = [NSString
> stringWithString: @"/Library/Application
> Support/Tunnelblick/Shared"]; 953 break; 954
> default: 955 break; 956 } 957
> } The purpose of this SUID helper is so that users can run OpenVPN
> with their own provided configuration files as root. OpenVPN
> configuration files can run scripts based on various OpenVPN
> events.
>
>
> 7. Race condition in process killing. 1496 BOOL isOpenvpn(pid_t
> pid) 1497 { 1498 BOOL is_openvpn = FALSE; 1499 int count
> = 0, 1500 i = 0; 1501 struct kinfo_proc* info = NULL; 1502
> 1503 getProcesses(&info, &count); 1504 for (i = 0; i < count;
> i++) { 1505 char* process_name = info[i].kp_proc.p_comm;
> 1506 pid_t thisPid = info[i].kp_proc.p_pid; 1507 if
> (pid == thisPid) { 1508 if (strcmp(process_name, "openvpn")==0)
> { 1509 is_openvpn = TRUE; 1510 } else { 1511 is_openvpn
> = FALSE; 1512 } 1513 break; 1514 } 1515 } 1516
> free(info); 1517 return is_openvpn; 1518 }
>
> 991 if(isOpenvpn(pid)) { 992 becomeRoot(); 993 didnotKill =
> kill(pid, SIGTERM); and 1022 if(strcmp(process_name, "openvpn")
> == 0) { 1023 becomeRoot(); 1024 didnotKill = kill(pid,
> SIGTERM);
>
> There's a race between checking the name of the process and
> killing that PID. Since PIDs are cycled, eventually that PID could
> point to a different process the user shouldn't have permission to
> kill.
>
>
> Hope this clarifies things. Let me know if you have more
> questions.
>
> Jason
>
- --
Kurt Seifried Red Hat Security Response Team (SRT)
PGP: 0x5E267993 A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993
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