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Re: Chrome V 124+ on MacOS - Virtual Server Access Issue

There is an if statement in the original iRule that checks the length of the collected payload and the indicated TLS record length contained within exactly match:

 

($payloadlen == $tls_recordlen+5)

 

...but Chrome's record length is now much larger than that (I am seeing values between 1730 and 1850, where I used to only see smaller values around 680).

 

I am experimenting with removing this specific check, so $payloadlen is not compared to $tls_recordlen (or is allowed to be >=) but I don't yet know if that will have a knock-on effect later in the script.

8 Replies

  • candc's avatar
    candc
    Icon for Cirrus rankCirrus

    OK, so my $payloadlen for Chrome is now always 1380, while my $tls_recordlen is always 1750+.  I'm guessing that 1380 is the MTU, so another TCP::collect needs to be worked into the procedure to capture the entire TLS record.

     

    Now, I remember reading somewhere that running multiple TCP::collect was A Bad Thing(TM), but I don't recall the exact reasoning...

    • candc's avatar
      candc
      Icon for Cirrus rankCirrus

      Brad_Baker  / LiefZimmerman  / Eric_Chen  / Stan_PIRON_F5 / Stanislas_Piro2 

      I have patched my copy of the original iRule with what I think is a working fix, but I would love if someone in the community could validate it, because my knowledge of the intricacies of the TLS packet is not strong.

      Essentially, I have replaced this if check in the original...

      # If valid TLS 1.X CLIENT_HELLO handshake packet
      if { [binary scan $payload cH4Scx3H4x32c tls_record_content_type tls_version tls_recordlen tls_handshake_action tls_handshake_version tls_handshake_sessidlen] == 6 && \
          ($tls_record_content_type == 22) && \
          ([string match {030[1-3]} $tls_version]) && \
          ($tls_handshake_action == 1) && \
          ($payloadlen == $tls_recordlen+5)} {

      ...with this block, which is intended to determine whether the reported TLS record length is longer than the payload we have and, if so, collect more packets until we have enough:

      # Keep collecting if CLIENT_HELLO messages that span more than one packet...
      if {![info exists payloadscan]} {
          set payloadscan [binary scan $payload cH4Scx3H4x32c tls_record_content_type tls_version tls_recordlen tls_handshake_action \
                                                              tls_handshake_version tls_handshake_sessidlen]
      }
      if {($payloadscan == 6)} {
          if {($tls_recordlen < 0 || $tls_recordlen > 16389)} {  # if we are asked to collect more than we will handle, bail...
              log local0.warn "[IP::remote_addr] : parsed TLS record length ${tls_recordlen} outside of handled length (0..16389)"
              reject
              return
          } elseif {($payloadlen < $tls_recordlen+5)} {          # if we have not collected enough yet, collect some more
              TCP::collect [expr {$tls_recordlen+5 - $payloadlen}]
              return
          }
      }
      
      # If valid TLS 1.X CLIENT_HELLO handshake packet
      if {($payloadscan == 6) && \
          ($tls_record_content_type == 22) && \
          ([string match {030[1-3]} $tls_version]) && \
          ($tls_handshake_action == 1) && \
          ($payloadlen == $tls_recordlen+5)} {

      This has allowed the rest of the original logic to capture the SNI server name and my services to resume operation.

      However, one new thing of note, is that the resulting values in $tls_handshake_preferred_version now include an extra value.  If I log this value, I can see...

      • Firefox returns 0304 0303 0302 0301
      • Chrome/Edge with --ssl-version-max=tls1.2 return 0303 only
      • Chrome/Edge v124 return xAxA 0304 0303

       

      The xAxA value changes every time -- so far, I have seen 1A1A, 7A7A, 8A8A, DADA and FAFA.  (I do not see a 7Fxy, as indicated in the switch statement).

      I am now wondering if this is just an implementation detail of the new Chrome TLS packet, or if I/we are now reading the preferred values from the wrong position in the payload.

      Is anyone able to verify the above?

      • candc's avatar
        candc
        Icon for Cirrus rankCirrus

        The 1A1A, 2A2A, etc values appear to align with a TLS extension called GREASE: and are probably OK.

        I would now just appreciate any confirmation that calling TCP::collect from within CLIENT_DATA isn't going to cause any problems later down the line.  At most I have tried to limit to two calls (the original one in CLIENT_ACCEPTED and one extra in CLIENT_DATA).

        There is one call to TCP::release at the end of CLIENT_DATA, but it is only reached if we have collected enough data across those two TCP::collect calls.

        So far, in my logging, the count of bytes released does appear to match the count of bytes collected -- I'm hoping that's all that needs to happen.