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Data loss prevention in file transfers

Within the territory of file transfer, data loss happens via information being inadvertently or intentionally sent to an unauthorized individual through the use of either file transfer software or file transfer protocols. It can also happen due to human ignorance or negligence - for example, uploading sensitive documents using an unapproved cloud provider.

Imagine a scenario where an employee in a large company has just transferred a series of files containing confidential data. Or another scenario where a small business owner has data residing on USB (unencrypted) and has since been lost.

It is with these two scenarios where we see data loss prevention not being applied for both data in transit (the transfer of files containing confidential information) and data at rest (the files residing within the USB).

Data at-rest

"Data at rest" specifically refers to old archived information. This information is of great concern to businesses and government institutions simply because the longer data is left unused in storage, the more likely it might be retrieved by unauthorized individuals. Protecting such data involves methods such as access control, data encryption and data retention policies.

Data in-use

"Data in use" refers to data that the user is currently interacting with. DLP systems that protect data in-use may monitor and flag unauthorized activities. These activities include screen-capture, copy/paste, print and fax operations involving sensitive data. It can be intentional or unintentional attempts to transmit sensitive data over communication channels.

Data in-motion

"Data in motion" is data that is traversing through a network to an endpoint destination. Networks can be internal or external. DLP systems that protect data in-motion monitor sensitive data traveling across a network through various communication channels.

DLP monitoring network activity

The DLP software is integrated into the network using a network TAP (terminal access point) port to perform real-time scanning and analysis of network traffic.

In addition to DLP inspection for data in-transit, DLP inspection can also be applied for data at-rest, such as within an FTPS or SFTP file server.

DLP and SFTPPlus MFT configuration options

For managed file transfer, data in-motion is of priority concern and is within the realm of control for file transfer software. Data at-rest is also another concern, but controls can also be distributed to controls permissioned by the OS file system.

The use of secure file transfer protocols as well as other processes for secure file transfer should form part of the stock for data loss prevention - transmission security. These services and configuration options can be configured using SFTPPlus.

An SFTPPlus feature, Digital signature validation can be configured to check if files have a valid signature:

SIGNED_CONTENT,SIGNATURE

The signature validation process is based on the RSA Digital Signature Algorithm PKCS#1 v2.1 also known as RSASSA-PSS and documented in RFC 3447.

Post process actions may also be added as part of the automated, client transfer rule in order to contain policy rules. A file dispatcher can then be set so that a transfer is quarantined via a separate folder if it has failed a policy rule.

A UUID prefix can also be appended to a file name in order to create unique names so that for each data uploaded, even if duplicate, there is a unique filename.

For authorization control, SFTPPlus administrators can apply permissions to specific groups or users. These permissions will help determine the access to which resources within the file transfer home directory of that user, and other the specific access rights. Permissions can also be set depending on regular expressions (regex), such as disallowing certain file formats. Through the options covered above, administrators can secure data or set permissions to ensure certain resources are not being inappropriately accessed or changed.

For more details about the above configuration options, please consult our documentation or talk to the Support team.

Audit trails for DLP

While operating, SFTPPlus will emit a set of events. Each event has a unique ID and defines a specific operation carried out by the server.

An example of an audit trail upon first connection to an FTP service is below:

| 20076 2018-03-07 19:44:05 ftp-only-1 Process 0.0.0.0:0 Service “ftp”
  started on “0.0.0.0:10023” using “ftp” protocol.
| 10033 2018-03-07 19:44:10 ftp-only-1 Unknown 127.0.0.1:51290
  New FTP/FTPS client connection made.

Administrators can gather a comprehensive picture of data-handling activities performed by users through the detailed, server-side audit trail. For example, see below audit trail for an attempt to access an authorized resource:

| 40007 2018-03-28 11:10:25 Process alice 127.0.0.1:52064 HTTP/HTTPS file access
  successfully started in "/ftps-folders/alice_files" as "/".

Through this online record of server events, organizations can be made aware for the purposes of any legal framework or compliance obligations.

Please see our Users Guides for specific examples pertaining to audit trails for HIPAA/HITECH, and GPG/PMO obligations. More articles are being written for other compliance and regulations.

Standard Operating Procedures (SOPs)

While the manual itself encompasses a wide range of topics from access controls to the use of ICT equipment, we have mapped components (SOPs) that is of direct or indirect relevance to file transfers involving SFTPPlus.

The following are Standard Operating Procedures (SOPs) as listed from page 36 of the ISM.

Access control

Procedure to be included: Authorising access rights to applications and data.

The SFTPPlus features that will help organizations meet this SOP include; ability to authorize access based on an existing authentication method (such as LDAP or operating system), ability to authorize or via an SFTPPlus application account.

Another example of rolling out proper access authorization is via permissions. User permissions can be set in the application based on extension (such as only making .exe files read-only) and directory (such as only allowing full control for certain folders).

Audit logs

Procedures to be included: Reviewing system audit trails and manual logs, particularly for privileged users.

For each server event that is emitted, this is logged within an audit trail that is available for SFTPPlus administrators. The example log below is of a user authenticating:

| 30014 2018-04-02 10:50:42 Process Unknown 127.0.0.1:50668 New SSH
  connection made.
| 20137 2018-04-02 10:50:42 single-server-uuid 127.0.0.1:50668 Account
  "erica" of type "os" authenticated as "erica" by os authentication
  "Operating System Accounts" using ssh-key.

Note that details such as the date, time, type of connection, type of authentication, account name and more are included in this audit log.

Data Transfers

Procedures to be included: Managing the review of media containing information that is to be transferred off-site. Managing the review of incoming media for viruses or unapproved software.

For the thorough review of media containing sensitive information, it is expected that SFTPPlus be integrated with a DLP (data leak prevention) software and other related policies to help prevent data leaks.

For the review of incoming media, SFTPPlus can also be integrated with antivirus checks as part of a file transfer process.

Our own customers are already integrating with a number of software that monitors and protects the boundary as part of their file transfer infrastructure.

System integrity audit

Procedures to be included: Reviewing user accounts, system parameters and access controls to ensure that the system is secure. Checking the integrity of system software. Testing access controls.

The text configuration server.ini file is available to review all configurations - from the authentication methods, configuration parameters and configuration options right through to the services being used.

The SFTPPlus Local Manager also includes the ability to review any changes made, before applying it to the system.

System maintenance

Procedures to be included: Managing the ongoing security and functionality of system software, including; maintaining awareness of current software vulnerabilities, testing and applying software patches /updates / signatures, and applying appropriate hardening techniques

SFTPPlus upgrades are designed to minimize disruption.

Initial configuration notes

If you are currently evaluating SFTPPlus, please follow our documentation to learn more about how you can configure your database and event handlers to suit your specifications.

Read more about configuring databases with SFTPPlus.

Read more about configuring event handlers. These provide further ways to configure SFTPPlus to create logging actions based on the events recorded.

Even if you are an existing customer, you can follow our documentation links above in order to refresh your knowledge on configuring SFTPPlus version 3. For those on legacy versions, please consult the documentation relevant to your version.

Example logs from SFTPPlus

The following are snippets when logging in for the first time from a GUI client to an SFTPPlus 3.30.0 SFTP server.

A new connection has been made to the service sftp-1. Knowing the service name is useful in case there are multiple other SFTP services running:

| 30014 2018-02-27 17:28:53 sftp-1 Unknown 127.0.0.1:58032
  New SSH connection made.
| 2018-02-27 17:28:53 30014 New SSH connection made.

The following are authentication methods associated with the server and confirmation of which methods are not active. There may be more methods, depending on how many of these are set up and enabled. To simplify the login process, please make sure to disable all unused authentication methods.:

| 20138 2018-02-27 17:28:55 some-http-auth-uuid Unknown 127.0.0.1:58032
  Ignoring http authentication "auth-over-remote-http" for "user" since it
  is not active.
| 2018-02-27 17:28:55 20138 Ignoring http authentication "auth-over-remote-http"
  for "user" since it is not active.
| 20138 2018-02-27 17:28:55 ldap-uuid Unknown 127.0.0.1:58032 Ignoring
  ldap authentication "LDAP against local test server" for "user" since it
  is not active.

The following logs list out a successful authentication of user using the ssh-key:

| 20137 2018-02-27 17:28:55 test-server-uuid Unknown 127.0.0.1:58032
  Account "user" of type "application" authenticated as "user" by
  application authentication "Application Accounts" using ssh-key.
| 2018-02-27 17:28:55 20137 Account "user" of type "application"
  authenticated as "user" by application authentication "Application
  Accounts" using ssh-key.

The following log message confirms the type of permissions allowed for the account and an active transfer that is already running:

| 20182 2018-02-27 17:28:55 Process user 127.0.0.1:58032 Account "user"
  logged in with permissions [[u'allow-full-control'], [u'/main_folder/*', u'allow-full-control'],
  [u'*.PDF', u'allow-read']]. Files uploaded as: test.txt

The following confirms that the user has logged into and now has access to the folder as the root ("/") folder:

| 30011 2018-02-27 17:28:55 Process user 127.0.0.1:58032 Subsystem SFTP
  successfully started in "/root/home/node/user/" as "/".
| 2018-02-27 17:28:55 30011 Subsystem SFTP successfully started in
  "/root/home/node/user/" as "/".
| 30060 2018-02-27 17:28:55 Process user 127.0.0.1:58032 Canonical file
  name requested for ".".
| 2018-02-27 17:28:55 30060 Canonical file name requested for ".".
| 30060 2018-02-27 17:28:55 Process user 127.0.0.1:58032 Canonical file
  name requested for "/.".
| 2018-02-27 17:28:55 30060 Canonical file name requested for "/.".
| 30019 2018-02-27 17:28:55 Process user 127.0.0.1:58032 Listing folder "/".
| 2018-02-27 17:28:55 30019 Listing folder "/".
| 30020 2018-02-27 17:28:55 Process user 127.0.0.1:58032 Successfully
  listed folder "/".
| 2018-02-27 17:28:55 30020 Successfully listed folder "/".

Initial configuration notes

If you are currently evaluating SFTPPlus, please follow our client side documentation.

The SFTPPlus Client software utilizes the command-line client-shell to access remote file servers using the interactive shell.

Even if you are an existing customer, you can follow our documentation links above in order to refresh your knowledge on configuring SFTPPlus version 3. For those on legacy versions, please consult the documentation relevant to your version.

Example logs from SFTPPlus

Let's connect with SFTPPlus Client using the SFTP protocol on port 10022. The following log details the UUID of the sftp service and confirms the connections:

| $ ./bin/client-shell.sh sftp://user@localhost:10022 -p pass
  --ssh-server-fingerprint 06:cb:46:2b:9a:9a:c4:10:54:f0:ea:2f:b6:05:cb:a0
| SFTPPlus (3.31.0) file transfer client shell
| > connect
| 20140 2018-03-05 16:40:59 51e1db00-8214-4b68-96fe-58470b8b2fc5 Process
  0.0.0.0:0 Connecting resource "sftp".
| 30072 2018-03-05 16:40:59 Process user localhost:10022 Location sftp
  connected to the SSH server.
| 30076 2018-03-05 16:40:59 Process user localhost:10022 Client SFTP
  subsystem initialized for location sftp.
| 20141 2018-03-05 16:40:59 51e1db00-8214-4b68-96fe-58470b8b2fc5 Process
  0.0.0.0:0 Resource "sftp" successfully connected.
| 20156 2018-03-05 16:40:59 51e1db00-8214-4b68-96fe-58470b8b2fc5 Process
  0.0.0.0:0 Successfully started location "sftp" of type sftp.

On the event that the SFTP connections fails, the log will state a number of details. The event ID is 30073. The event will communicat the host key algorithm that is in use to identify the server-side, the cipher used to receive data, the HMAC for both sent and received data, key exchange algorithm, cipher used for sent data and the name of the location associated for this event. Below is an example of the event that has been emitted has part of this new SFTP connection.:

| 30073 2018-03-05 16:36:16 Process user localhost:10022 Connection to
  SSH server was lost for location sftp. Protected using host-key:ssh-rsa key-exchange:
  diffie-hellman-group-exchange-sha256 in-hmac:hmac-sha2-256
  in-cipher:aes256-ctr out-hmac:hmac-sha2-256 out-cipher:aes256-ctr

Providing that the SFTP connection succeeds, supported actions are logged as either a success like below:

| > gattrs remote_get
| 60071 2018-03-05 16:41:22 Process Process 0.0.0.0:0 Successfully got
  attributes for "Reports_2018" on "sftp".
| name: Reports_2018
| path: Reports_2018
| size: 128
| modified: 2018-02-16 16:15:21
| is_file: False
| is_folder: True

Or error details are caught with an explanation message as to why:

| > get unknown_file
| 20145 2018-03-05 16:42:08 Process Process 0.0.0.0:0 Failed to resolve
  text for event id "60054" with data "{'path': 'unknown_file\xc8\x9bu',
  'location': u'sftp', 'avatar':
  <chevah.server.identity.avatar.ProcessAvatar object at 0x10efc3110>,
  'details': "'ascii' codec can't decode byte 0xc8 in position 9: ordinal
  not in range(128)"}". 'ascii' codec can't decode byte 0xc8 in position
  9: ordinal not in range(128)

Initial configuration notes

Following from that, you can use the built-in the client-side or server-side software that you are utilizing. SFTPPlus offers logging functionalities both for the client-side and server-side. Network administrators using other software, such as sftp -vvv, for client or server may wish to use additional logging functionalities.

Example with sftp -vvv output

These lines mean that SSH protocol 2.0 is being utilized with the version of OpenSSH:

debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.6

This line indicates which protocol version is in use service-side and which version:

debug1: Remote protocol version 2.0, remote software version SFTPPlus_3.30.0

This indicates which algorithms are preferred. You may opt to only select the strongest availability supported in your system first. In this case the ordering is logical as it moves from the more secure algorithm down to a less secure algorithm.:

| debug3: order_hostkeyalgs: prefer hostkeyalgs:
  ssh-rsa-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa

These are the key exchange algorithms that are available.:

| debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,
  ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
  diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,
  diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha1,
  diffie-hellman-group14-sha256,diffie-hellman-group14-sha1,ext-info-c

These are the host key algorithms.:

| debug2: host key algorithms: ssh-rsa-cert-v01@openssh.com,rsa-sha2-512,
  rsa-sha2-256,ssh-rsa,ecdsa-sha2-nistp256-cert-v01@openssh.com,
  ecdsa-sha2-nistp384-cert-v01@openssh.com,
  ecdsa-sha2-nistp521-cert-v01@openssh.com,ssh-ed25519-cert-v01@openssh.com,
  ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519

These are the ciphers used from client to server (ctos) and from server to client (stoc):

| debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,
  aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com

| debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,
  aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com

These are the ciphers used from client to server (ctos) and from server to client (stoc):

| debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
  hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
  hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,
  hmac-sha2-256,hmac-sha2-512,hmac-sha1

| debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
  hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
  hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,
  hmac-sha2-256,hmac-sha2-512,hmac-sha1

These are the compression algorithms used from client to server (ctos) and from server to client (stoc):

debug2: compression ctos: none,zlib@openssh.com,zlib
debug2: compression stoc: none,zlib@openssh.com,zlib

This is the key exchange initialized proposal from the host server:

| debug2: peer server KEXINIT proposal
| debug2: KEX algorithms: diffie-hellman-group-exchange-sha256,
  diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1,
  diffie-hellman-group14-sha1
| debug2: host key algorithms: ssh-dss,ssh-rsa
| debug2: ciphers ctos:
  aes256-ctr,aes256-cbc,aes192-ctr,aes192-cbc,aes128-ctr,aes128-cbc,
  3des-ctr,3des-cbc
| debug2: ciphers stoc:
  aes256-ctr,aes256-cbc,aes192-ctr,aes192-cbc,aes128-ctr,aes128-cbc,
  3des-ctr,3des-cbc
| debug2: MACs ctos: hmac-sha2-256,hmac-sha1
| debug2: MACs stoc: hmac-sha2-256,hmac-sha1
| debug2: compression ctos: none,zlib
| debug2: compression stoc: none,zlib

These are the key exchange algorithms used from server to client and client to server:

| debug1: kex: algorithm: diffie-hellman-group-exchange-sha256
| debug1: kex: host key algorithm: ssh-rsa
| debug1: kex: server->client cipher: aes128-ctr MAC: hmac-sha2-256
  compression: none
| debug1: kex: client->server cipher: aes128-ctr MAC: hmac-sha2-256
  compression: none

This is the SSH version 2 key exchange Diffie-Hellman Group Exchange request. This specifies the size of the SSH prime moduli being calculated by the SFTP server as indicated in the SFTPPlus /configuration/ file. When you first initialize SFTPPlus version 3, the Time Type Tests Tries Size Generator Modulus is generated and saved in ssh-service.moduli. This file contains primes ranging in size from 1023 to 8191 bits. An example of the contents for the .moduli file is below:

| 20060827134212 2 6 100 3071 2
  D3230D237572ECE9F92358715EBAC3A4D89F2D6B4DC39F056450263BEF1665FBD
  7B93916ABC867B7064802159D273C7EB01C5F9281A3D6DCCB7CF997D385998EC0E1FA3319AFE771A90ADBACEB414A02
  0630D7C7F161FAFEC6C9FC06D3205C712AAE8848A1B2C21DFF301C7FFC0B75D13F060A313C32AFEEAF1493F641760EB
  EF38829B3371699D2A3264D0ECEB4E5C19581ED8C57699F559B9828BBFE147952E289F0E171C9C60335DD2F492CB409
  A4DB97BDF86E2DBA605064DB040A3DF5678E24F66718CA115C95C892FF7AEDFAABC2E6414716298CEC1A604270FEADF
  191B7C8A59C238C395A65442C0B963BF83025BED3951A271B7440EC7687C31DE63355DA7FEAC15DC962C7BF7614EB59
  B077B9889AD8703DFE98AC99615B722A0ABE89956D1058E025C7733420CB51D7E1608EFF2C0A30C9A5EB77CCA02C6B0
  0CE781B172001C6C458630890062E27CE307D513A7686A69D1D548DE8334B13136D9E842A5E17FD67522C93823E03F0
  8AEE8024AF5D88B2EE01D4D9980084EFD5D943

In the following example below, a SSH moduli prime from 2048 to 8192 bits are used. Specifically, a moduli with a range from 4092 to 8192 are sent for the SSH message key exchange Diffie-Hellman group exchange request as indicated on debug1 line below (SSH2_MSG_KEX_DH_GEX_REQUEST(2048<8192<8192)) Once sent, the server uses the moduli file, the same file that was initialized as part of the SFTPPlus installation steps, in order to crack the shared secret. The server provides its host key back to the client along with the algorithm used as indicated by the final line as Server host key: ssh-rsa SHA256:hdSfa7gb2O984malHerkwerj3m20dHb6Yuwl0&hbxFj.

See the rest of the output below:

| debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(2048<8192<8192) sent
| debug3: receive packet: type 31
| debug1: got SSH2_MSG_KEX_DH_GEX_GROUP
| debug2: bits set: 4092/8192
| debug3: send packet: type 32
| debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
| debug3: receive packet: type 33
| debug1: got SSH2_MSG_KEX_DH_GEX_REPLY
| debug1: Server host key: ssh-rsa
  SHA256:hfSfa0gb2O884malLerkwerj3m20dBb6Yuwl0&hbxGj

The client then checks to see if the host key is located within the known_hosts file:

| debug3: hostkeys_foreach: reading file "/root/home/node/.ssh/known_hosts"
| debug3: record_hostkey: found key type RSA in file
  /root/home/node/.ssh/known_hosts:8
| debug3: load_hostkeys: loaded 1 keys from [12.345.678.90]:10022

A few more steps occur to verify this server host name and port:

ddebug1: Host '12.345.678.90]:10022' is known and matches the RSA host key.
ddebug1: Found key in /root/home/node/.ssh/known_hosts:8

This is the server rekey interval:

debug1: rekey after 4294967296 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug3: receive packet: type 21
debug1: SSH2_MSG_NEWKEYS received
debug2: set_newkeys: mode 0
debug1: rekey after 4294967296 blocks

The following are SSH keys found:

debug2: key: imported-openssh-key (0x7e403ff95550), agent
debug2: key: /root/home/node/.ssh/id_rsa (0x0)
debug2: key: /root/home/node/.ssh/id_dsa (0x0)
debug2: key: /root/home/node/.ssh/id_ecdsa (0x0)
debug2: key: /root/home/node/.ssh/id_ed25519 (0x0)

The following are authentication methods that can continue, the preferred authentication order, remaining preferred:

| debug3: send packet: type 5
| debug3: receive packet: type 6
| debug2: service_accept: ssh-userauth
| debug1: SSH2_MSG_SERVICE_ACCEPT received
| debug3: send packet: type 50
| debug3: receive packet: type 51
| debug1: Authentications that can continue: password,publickey
| debug3: start over, passed a different list password,publickey
| debug3: preferred publickey,keyboard-interactive,password
| debug3: authmethod_lookup publickey
| debug3: remaining preferred: keyboard-interactive,password
| debug3: authmethod_is_enabled publickey
| debug1: Next authentication method: publickey
| debug1: Offering public key: RSA
  SHA256:F8zPRFytcYU8PERggkPDs+D32TRgvVm4H3BBJduo+de
  /root/home/node/.ssh/id_rsa
| debug3: send_pubkey_test
| debug3: send packet: type 50
| debug2: we sent a publickey packet, wait for reply

The server will go through the exchange to authenticate until the final preferred method is reached - the password method. Upon success, the client enters an interactive session with the server.

There will also be additional verbose logs after entering an interactive session, such as a brief snippet below:

debug2: fd 6 setting TCP_NODELAY
debug3: ssh_packet_set_tos: set IP_TOS 0x08
debug2: client_session2_setup: id 0
debug1: Sending environment.
debug3: Ignored env _system_type
debug1: Sending env LANG = en_CA.UTF-8
debug2: channel 0: request env confirm 0
debug3: send packet: type 98
debug3: Ignored env _system_arch
debug3: Ignored env XPC_FLAGS
debug3: Ignored env _system_version
debug3: Ignored env XPC_SERVICE_NAME
debug3: Ignored env rvm_version
debug3: Ignored env _system_name
debug1: Sending subsystem: sftp