Vulnerability Note VU#840249

Wind River Systems VxWorks weak default hashing algorithm in standard authentication API (loginLib)

For instance, when the default 'target/password' login example is used, 'y{{{{{kS' hashes to the same string as 'password'. It is thus possible to login using both 'password' and 'y{{{{{kS' as the passwords for the user 'target'.

Additional information can be found in ICS-CERT advisory ICSA-10-214-01 and on the Metasploit Blog.

II. Impact

In addition, and so as to avoid registration of the default 'target'/'password' credentials at init time, the LOGIN_USER_NAME and LOGIN_USER_PASSWORD project parameters/#defines should be set to empty strings (so that no user is registered using the default encryption routine). Only after the new encryption routine is registered should new users be added to the system.

loginEncryptInstall allows the user to install a custom encryption routine. The custom routine <rtn> must be of the following form:

STATUS encryptRoutine
       (
       char *password,               /* string to encrypt    */
       char *encryptedPassword       /* resulting encryption */
       )

The <encryptedPassword> string length should be no more than :
+ VxWorks 6.4 and below: 80 characters
+ VxWorks 6.5 and above: 128 characters

When a custom encryption routine is installed, a host version of this routine must be written to replace the tool vxencrypt in host/<hostOs>/bin.

Appendix #1 shows example code making use of loginEncryptInstall() to set a custom encryption routine. Depending on the VxWorks version used, either SHA-512 or SHA-256 are used.

DISCLAIMER: The following example code was provided by Wind River Systems. It is for demonstration purposes only and should not be used as is.

APPENDIX #1
/* Sample loginEncryptInstallCode() */

/* includes */

#include <vxWorks.h>
#include <errnoLib.h> /* for errnoGet API */
#include <fcntl.h> /* for open API */
#include <stdio.h> /* for sprintf API */
#include <string.h> /* for string handling */
#include <unistd.h> /* for close API */
#include <loginLib.h>   /* library under test */
#include <sysSymTbl.h> /* for sySymTbl variable */

/* globals */

/*
 * SHA-512 and SHA-256 digests corresponding to the 'vincent' string.
 * VxWorks 6.4 and below use SHA-256 because of the 80 chars
 * loginEncryptInstall() digest limit, while post 6.5 versions use SHA-512.
 */

#if ((_WRS_VXWORKS_MAJOR == 6) && (_WRS_VXWORKS_MINOR > 4))
char * cryptSha = "38256fbe4e80d9ffd355409f36238ae18e62c668208c259e60"
 "ca323ab47cf55b8656e88e56593d531b250aae2c35376b387d"
 "83ade5e3e8b6c042133b97030fa4";
char * shaIdent = "SHA-512";
#else
char * cryptSha = "65c3f75641b22925c737ca657b126cd68c39e423349d43031c"
 "f9a3b9a18cee1f";
char * shaIdent = "SHA-256";
#endif

/* locals */

LOCAL STATUS fixed_sha (char* password, char* encryptedpassword);

/*******************************************************************************
*
* loginEncryptInstallExample - register and use a custom encryption routine
*
* RETURNS: N/A
*/

STATUS loginEncryptInstallExample (void)
    {
    char* name = "vincent";
    char* passwd = "vincent";
    STATUS status = ERROR;

    /* Register our new encryption routine */

    loginEncryptInstall (fixed_sha, 0);
    printf ("Registered %s encryption routine.\n", shaIdent);

    /* Add a new user using this encryption routine */

    if (loginUserAdd (name, cryptSha) != OK)
        {
printf ("Unable to add new user to system using %s encryption"
"routine [errno = %#x].\n", shaIdent, errnoGet ());

        return ERROR;
        }
    else
        {
/* Launch the verification process */

if (loginUserVerify (name, passwd) != OK)
   {
   printf ("Successfully registered and added a new user "
   "with custom encryption routine but password "
   "check failed [errno = %#x].\n", errnoGet ());

   goto cleanup;
   }
else
   {
   printf ("Successfully used custom encryption routine "
   "(routine registration, user creation and "
   "verification).\n");
   }
}

    status = OK;

cleanup:

    /* Remove user and module; unregister routine */

    if (loginUserDelete (name, passwd) != OK)
{
printf ("There was a problem while trying to delete the "
"newly added user during cleanup [errno = " "%#x].\n",
errnoGet ());
status = ERROR;
}

    loginEncryptInstall ((FUNCPTR) loginDefaultEncrypt, 0);
    return status;
    }

/******************************************************************************
* fixed_sha - returns a fixed SHA digest
*
* RETURNS: Always OK
*/

LOCAL STATUS fixed_sha
    (
    char* password,
    char* encryptedpassword
    )
    {
    /*
     * IMPORTANT : This test routine should be replaced by a real SHA
     * generator. Because of the fixed digest, the current version does not
     * perform actual user validation (i.e all passwords are accepted for user
     * 'vincent').
     */

    strcpy (encryptedpassword, cryptSha);
    return OK;
    }

Restrict access
Appropriate firewall rules should be implemented to restrict access to any services that use the standard authentication API.

Disable services
Services such as FTP or telnet should be disabled if not needed.

Monitor access
IDS signatures should be implemented to detect brute force attacks to services that use the standard authentication API.

Vendor Information

http://blog.metasploit.com/2010/08/vxworks-vulnerabilities.html
http://www.us-cert.gov/control_systems/pdf/ICSA-10-214-01_VxWorks_Vulnerabilities.pdf
http://blogs.windriver.com/chauhan/2010/08/vxworks-secure.html
https://support.windriver.com/olsPortal/faces/maintenance/downloadDetails.jspx?contentId=033709
http://newsoft-tech.blogspot.com/2010/09/follow-up-on-vxworks-issue.html
http://cvk.posterous.com/how-to-crack-vxworks-password-hashes

Credit

Thanks to HD Moore for reporting this vulnerability.

This document was written by Jared Allar.

Other Information

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