Check Point Software Technologies - Vulnerability Discovery Team (VDT)
http://www.checkpoint.com/defense/

rpc.pcnfsd syslog format string vulnerability
CVE-2010-1039

INTRODUCTION

There exists a vulnerability within a log function of the rpc.pcnfsd service
which when properly exploited can lead to remote compromise of the vulnerable 
system.
This vulnerability was confirmed in the following versions and operating
systems, other versions and operating systems may be also affected.

IBM AIX 6.1.0 and lower
IRIX 6.5
HP-UX 11.11, 11.23, 11.31

DETAILS

This vulnerability can be triggered by sending a rpc request resulting in an
invalid directory causing the service to call _msgout() function that call 
syslog() function to log the error without checking for formatted strings.

This is the vulnerable function (pcnfsd version 1.2 source).

from pcnfsd_print.c

psrstat pr_start2(system, pr, user, fname, opts, id)

...
...            

if (rename(pathname, new_pathname)) 
                   
{
/*
           
**---------------------------------------------------------------
                   
** Should never happen.     
           
**---------------------------------------------------------------
           
*/
                   
(void)sprintf(tempstr, "rpc.pcnfsd: spool file rename (%s->%s) failed.\n",
                                                pathname, new_pathname);
                
msg_out(tempstr);                        <---- Vuln Function with our input



form pcnfsd_xdr.c

static
_msgout(msg)                                                                           
                char *msg;
{
#ifdef RPC_SVC_FG
                if (_rpcpmstart)
                                syslog(LOG_ERR, msg);                <---- Problem here!
                else
                                (void) fprintf(stderr, "%s\n", msg);
#else
                syslog(LOG_ERR, msg);                                <---- Problem here!
#endif
                return(0);
}


GDB output:

Program received signal SIGSEGV, Segmentation fault.
0xd01e28cc in _doprnt () from /usr/lib/libc.a(shr.o)
(gdb) bt
#0  0xd01e28cc in _doprnt () from /usr/lib/libc.a(shr.o)
#1  0xd01dd4fc in vfprintf () from /usr/lib/libc.a(shr.o)
#2  0xd024be10 in __syslog_r () from /usr/lib/libc.a(shr.o)
#3  0xd024c400 in syslog () from /usr/lib/libc.a(shr.o)
#4  0x10000d98 in ?? ()



CREDITS

This vulnerability was discovered and exploited by Rodrigo Rubira Branco from Check Point Vulnerability Discovery Team (VDT).