RADIUS server using APM to authenticate users

Problem this snippet solves:

this code convert APM policy to a RADIUS server.

Code description

When a Radius request is accepted by the VS:

• the radius client IP address is checked against a Datagroup list.

  • if in list : The shared secret is extracted from Datagroup list
  • if not : drop the packet

• the password is decrypted with radius secret

• if request code is Access-Request, an APM session is created and radius attributes are set as session variable (including username and password)

• Access session is evaluated and return

  allow

  or

  deny

  result

• If the Access policy include radius attribute stored in variable

  session.result.radius_attr

  , attributes are added to the radius response

• return Access-Accept or Access-Reject response code based on the session result.

Supported request Packet types:

• Access-Request (1)

Returned Packet types:

• Access-Accept (2)
• Access-Reject (3)

Required request attributes

• User-Name (1)
• User-Password (2)

Optional request attributes

• NAS-IP-Address (4) : IP address
• NAS-Port (5) : Integer
• NAS-Identifier (32) : String
• NAS-Port-Type (61) : Integer

All other attributes are ignored by this irule

Supported response Attributes

All RFC2865 attributes are allowed. Vendor specific attributes are not supported yet.

Note : First version of this code was an enhancement of John McInnes RADIUS Server iRule who had to parse all RADIUS Data (RADIUS::avp did not exist when he wrote it's irule). The irule structure is still the same, but binary operations are optimized and more than 16 bytes passwords support is now included. thanks to Kai Wilke who show previous limitations and leads me to the right direction on how to decode long passwords.

Versions :

1.0 : First version based on RADIUS commands. Required RADIUS profile assigned to the virtual server

1.1 : Added Request Message-Authenticator attribute validation / Response Message-Authenticator insertion (Asked by Sam Hall). To support this feature, the code is rewritten to decode binary data. Radius profile is not required anymore. (31/05/2018)

1.2 : correction on the Request Message-Authenticator attribute validation, a binary conversion to same type is required after

[string replace ...]

1.3 : Changed Datagroup radius_clients values format to list of parameters and values. this allow to configure per radius client parameters instead of global parameters (Message-Authenticator validation, ...) (1/06/2018)

1.4 : Security improvement while decoding packet (default decoded integer are signed values, where packet decoding length must be unsigned integer. Thank you Kai wilke for the advices) and added duplicate packet detection (4/06/2018)

How to use this snippet:

1. Create an Access Policy authenticating users.
2. Define Access profile name in variable

   static::apmpolicy

3. create a data group list

   radius_clients

   with values:

   IPAddress := "KEY radius\\ secret [REQMSGAUTH_REQUIRE 1] [RESPMSGAUTH_INSERT 1] [RFC_2865_COMPLIANCE 1]"
   IPAddress := "KEY another\\ radius\\ secret [REQMSGAUTH_REQUIRE 1] [RESPMSGAUTH_INSERT 0] [RFC_2865_COMPLIANCE 1]"
   

   • KEY parameter must be followed by the shared secret, if it contains space, add 2 \ characters before each space. this parameter is required.
   • REQMSGAUTH_REQUIRE (optional) define if Message-Authenticator attribute is required in request. default value is 0* RESPMSGAUTH_INSERT (optional) define if Message-Authenticator attribute is inserted in response. default value is 0
   • RFC_2865_COMPLIANCE (optional) define if the request must respect RFC 2865 (required attributes). default value is 0

4. create a virtual server with RADIUS profile to manage RADIUS::avp commands. If you requires to add radius attributes in RADIUS response, create the APM variable session.result.radius_attr with text value (one line, space characters must be escaped):

   Attribute1ID Attribute1Value Attribute2ID Attribute2Value Attribute3ID Attribute3Value
   

   example :

   18 Authentication\ Successful 27 3600
   

Code :

when RULE_INIT {
   set static::apmpolicy "/Common/AP_RADIUS_SERVICE"
   set static::client_list "radius_clients"
}

when CLIENT_ACCEPTED {
  binary scan [md5 [UDP::payload]] H* PAYLOAD_HASH
  switch [set DUPLICATE_RESPONSE [table lookup -subtable [IP::client_addr] $PAYLOAD_HASH]] {
    "" {
      # Do nothing, not in table
    }
    drop {
      log local0. "Duplicate packet detected with drop decision... dropping again"
      UDP::drop; return
    }
    default {
      log local0. "Duplicate packet detected sending same answer from table"
      UDP::respond [binary format H* $DUPLICATE_RESPONSE]
      return
    }
  }
  
   set RespLength 20
   set RespAVP ""
   ############## START OF ALLOWED RADIUS CLIENT IP VALIDATION #################
   if {![class match [IP::client_addr] equals $static::client_list]} {
      log local0. "RADIUS Client not in Datagroup : [IP::client_addr]"
      # RFC 2865 : A request from a client for which the RADIUS server does not have a shared secret MUST be silently discarded
      table add -subtable [IP::client_addr] $PAYLOAD_HASH "drop" 30 600
      UDP::drop
      return
   }
   # Set default values if Datagroup miss this configuration
   set RADCLIENT(REQMSGAUTH_REQUIRE) 0
   set RADCLIENT(RESPMSGAUTH_INSERT) 0
   set RADCLIENT(RFC_2865_COMPLIANCE) 1
    #Retreive RADIUS client shared secret and radius client capabilities.
   array set RADCLIENT [class match -value [IP::client_addr] equals $static::client_list]
   if {[binary scan [UDP::payload] cH2Sa16 QCODE IDENTIFIER QLEN Q_AUTHENTICATOR] != 4 || [set QLEN [expr {$QLEN & 0xFFFF}]] > [UDP::payload length] || $QLEN > 4096} {
      table add -subtable [IP::client_addr] $PAYLOAD_HASH "drop" 30 600
      UDP::drop
      return
   } else {
    # Store only PAYLOAD in variable if Length field is valid (less than 4096 and less than payload length). prevent variable allocation if payload not valid.
    # Octets outside the range of the Length field MUST be treated as padding and ignored on reception.
    set PAYLOAD [UDP::payload $QLEN]
   }
    switch $QCODE {
      1 {
        set REQUEST_NOT_ALLOWED 0
        #Store All attribute in array QUERY_ATTR with Attrbute ID as Key
        for {set record_offset 20} {$record_offset < $QLEN } {incr record_offset $QAVP_LEN} {
           # If an Attribute is received in an Access-Accept, Access-Reject or Access-Challenge packet with an invalid length, 
           # the packet MUST either be treated as an Access-Reject or else silently discarded.
           if {([binary scan $PAYLOAD @${record_offset}cc QAVP_TYPE QAVP_LEN] != 2) || ([set QAVP_LEN [expr {$QAVP_LEN & 0xFF}]] < 3) || ($record_offset+$QAVP_LEN > $QLEN) } {
              table add -subtable [IP::client_addr] $PAYLOAD_HASH "drop" 30 600
              UDP::drop
              return
            }
           switch -- [set QAVP_TYPE [expr { $QAVP_TYPE & 0xFF}]] {
              1 - 2 - 3 - 4 - 5 - 24 - 32 - 61 {binary scan $PAYLOAD @${record_offset}x2a[expr {$QAVP_LEN -2}] QUERY_ATTR($QAVP_TYPE)}
              80 {
                binary scan $PAYLOAD @${record_offset}x2a[expr {$QAVP_LEN -2}] QUERY_ATTR($QAVP_TYPE)
                binary scan [string replace $PAYLOAD $record_offset [expr {$record_offset + 18}] [binary format ccH32 80 18 [string repeat 0 32]]] a* UNSIGNED_REQUEST
              }
          }
        }
        #Assign attibutes to expected variable, with decoding if required. 
        set USER_NAME [expr {[info exists QUERY_ATTR(1)] ? $QUERY_ATTR(1) : ""}]
        set USER_PASSWORD [expr {[info exists QUERY_ATTR(2)] ? $QUERY_ATTR(2) : ""}]
        set CHAP_PASSWORD [expr {[info exists QUERY_ATTR(3)] ? $QUERY_ATTR(3) : ""}]
        if {[info exists QUERY_ATTR(4)]} {binary scan $QUERY_ATTR(4) c4 octets; foreach octet $octets {lappend r [expr {$octet & 0xFF}]}; set NAS_IP_ADDRESS  [join $r .] } else {set NAS_IP_ADDRESS "" }
        if {[info exists QUERY_ATTR(5)]} {binary scan $QUERY_ATTR(5) I NAS_PORT; set NAS_PORT [expr {$NAS_PORT & 0xFFFFFFFF}] } else {set NAS_PORT "" }
        set STATE [expr {[info exists QUERY_ATTR(24)] ? $QUERY_ATTR(24) : ""}]
        set NAS_IDENTIFIER [expr {[info exists QUERY_ATTR(32)] ? $QUERY_ATTR(32) : ""}]
        #if {[info exists QUERY_ATTR(61)]} {binary scan $QUERY_ATTR(61) I NAS_PORT_TYPE; set NAS_PORT_TYPE [expr {$NAS_PORT_TYPE & 0xFFFFFFFF}] } else {set NAS_PORT_TYPE "" }
        set MESSAGE_AUTHENTICATOR [expr {[info exists QUERY_ATTR(80)] ? $QUERY_ATTR(80) : ""}]
        #EVALUATE REQUEST MESSAGE-AUTHENTICATOR
        if {$RADCLIENT(REQMSGAUTH_REQUIRE) && ($MESSAGE_AUTHENTICATOR equals "" || ![CRYPTO::verify -alg hmac-md5 -key $RADCLIENT(KEY) -signature $MESSAGE_AUTHENTICATOR $UNSIGNED_REQUEST])} {
          # RFC 2869 : A RADIUS Server receiving an Access-Request with a Message-Authenticator Attribute present MUST calculate the correct value
          # of the Message-Authenticator and silently discard the packet if it does not match the value sent.
          log local0. "[IP::client_addr] : wrong or missing Message-Authenticator attribute"
          table add -subtable [IP::client_addr] $PAYLOAD_HASH "drop" 30 600
          UDP::drop
          return
        }
         if {$RADCLIENT(RFC_2865_COMPLIANCE)} {
            if {$NAS_IP_ADDRESS == "" && $NAS_IDENTIFIER == ""} {
               # RFC 2865 : It MUST contain either a NAS-IP-Address attribute or a NAS-Identifier attribute (or both).
               set REQUEST_NOT_ALLOWED 1
               set RAVP(18) "REQUEST NOT RFC COMPLIANT"
            } elseif {$USER_PASSWORD == "" && $CHAP_PASSWORD == "" && $STATE == ""} {
               # RFC 2865 : An Access-Request MUST contain either a User-Password or a CHAP-Password or a State.
               set REQUEST_NOT_ALLOWED 1
               set RAVP(18) "REQUEST NOT RFC COMPLIANT"
            } elseif {$USER_PASSWORD ne "" && $CHAP_PASSWORD ne ""} {
               # RFC 2865 : An Access-Request MUST NOT contain both a User-Password and a CHAP-Password.
               set REQUEST_NOT_ALLOWED 1
               set RAVP(18) "REQUEST NOT RFC COMPLIANT"
            }
         }
         if {$USER_PASSWORD == ""} {
            set REQUEST_NOT_ALLOWED 1
            set RAVP(18) "USER-PASSWORD NOT SET BUT REQUIRED"
         } elseif {$USER_NAME == ""} {
            set REQUEST_NOT_ALLOWED 1
            set RAVP(18) "USER-NAME NOT SET BUT REQUIRED"
         } 
      }
      2 - 3 - 11 {
         set REQUEST_NOT_ALLOWED 1
         set RAVP(18) "RADIUS CODE NOT SUPPORTED - NOT A RADIUS CLIENT"
      }
      4 - 5 - 6 - 10 {
         set REQUEST_NOT_ALLOWED 1
         set RAVP(18) "RADIUS CODE NOT SUPPORTED - NOT A RADIUS ACCOUNTING SERVER"
      }
      default {
         set REQUEST_NOT_ALLOWED 1
         set RAVP(18) "RADIUS CODE NOT SUPPORTED"
      }
   }
   ############## END OF RFC COMPLIANCE AND SERVER FEATURES VALIDATION #################
   # DO NOT RELEASE UDP PACKET. Drop it to prevent further process by irule or load balancing to an internal server.
   # When UDP packet dropped, PAYLOAD is dropped and RADIUS Commands not available anymore.
   UDP::drop
   if {$REQUEST_NOT_ALLOWED == 0} {
      ########## START OF PASSWORD DECRYPTION ############################
      binary scan [md5 "$RADCLIENT(KEY)$Q_AUTHENTICATOR"] H* bx_hex
      binary scan $USER_PASSWORD H* px_full_hex
      set Password_Padded ""
      for {set x 0} {$x<[string length $px_full_hex]} {set x [expr {$x+32}]} {
         set px_hex [string range $px_full_hex $x [expr {$x+31}]]
         append Password_Padded [binary format W [expr 0x[string range $px_hex 0 15] ^ 0x[string range $bx_hex 0 15]]]
         append Password_Padded [binary format W [expr 0x[string range $px_hex 16 31] ^ 0x[string range $bx_hex 16 31]]]
         binary scan [md5 "$RADCLIENT(KEY)[binary format H* $px_hex]"] H* bx_hex
      }
      binary scan $Password_Padded A* PASSWORD
      ########## END OF PASSWORD DECRYPTION ############################

      ########## START OF APM AUTHENTICATION ############################
      set flow_sid [ACCESS::session create -timeout 60 -lifetime 300]
      ACCESS::policy evaluate -sid $flow_sid -profile $static::apmpolicy \
         session.logon.last.username $USER_NAME \
         session.logon.last.password $PASSWORD \
         session.server.landinguri "/" \
         session.logon.last.NAS_IP_Address $NAS_IP_ADDRESS \
         session.logon.last.NAS_Port $NAS_PORT \
         session.logon.last.NAS_Identifier $NAS_IDENTIFIER \
         session.logon.last.NAS_Port_Type $NAS_PORT
      if {[ACCESS::policy result -sid $flow_sid] equals "allow"} {
         set ResponseCode 2
         if {![info exists RAVP(18)] } {set RAVP(18) "Good username Password"}
      } else {
         set ResponseCode 3
         if {![info exists RAVP(18)] } {set RAVP(18) "wrong username Password"}
      }
      array set RAVP [ACCESS::session data get -sid $flow_sid session.result.radius_attr]
      ACCESS::session remove -sid $flow_sid
      ########## END OF APM AUTHENTICATION ############################
   } else {
      set ResponseCode 3
      if {[info exists RAVP(18)] } { log local0. $RAVP(18)}
   }

   ########## ENCODING AND DELIVERY OF RADIUS RESONSE ############################
   foreach attrID [array names RAVP] {
      incr RespLength [set attrLength [expr {[string length $RAVP($attrID)]+2}]]
      append RespAVP [binary format cca* $attrID $attrLength $RAVP($attrID)]
   }
   #CALCULATE RESPONSE MESSAGE-AUTHENTICATOR
   if {$RADCLIENT(RESPMSGAUTH_INSERT)} {
    set UNSIGNED_RespAVP $RespAVP[binary format ccH32 80 18 [string repeat 0 32]]
    incr RespLength 18
    append RespAVP [binary format cc 80 18][CRYPTO::sign -alg hmac-md5 -key $RADCLIENT(KEY) [binary format cH2Sa16a* $ResponseCode $IDENTIFIER $RespLength $Q_AUTHENTICATOR $UNSIGNED_RespAVP]]
    }

   binary scan [md5 [binary format cH2Sa16a[expr {$RespLength-20}]a[string length $RADCLIENT(KEY)] $ResponseCode $IDENTIFIER $RespLength $Q_AUTHENTICATOR $RespAVP $RADCLIENT(KEY) ]] H* ResponseAuth
   set RESPONSE [binary format cH2SH32a* $ResponseCode $IDENTIFIER $RespLength $ResponseAuth $RespAVP]
   UDP::respond $RESPONSE
   binary scan $RESPONSE H* RESPONSE_HEX
   table add -subtable [IP::client_addr] $PAYLOAD_HASH $RESPONSE_HEX 15 60
}

Tested this on version: