Background For regular, unencrypted FTP traffic, the FTP ALG can inspect the unencrypted control channel and open related sessions for the FTP data channel. These related sessions (gates) are specific to source and destination IPs and ports of client and server. The design intent of the ftps-extensions option (which is disabled by default) is to provide similar functionality when the SRX secures the FTP/FTPS client. As the control channel is encrypted, the FTP ALG cannot inspect the port specific information and will open a wider TCP data channel (gate) from client IP to server IP on all destination TCP ports. In FTP/FTPS client environments to an enterprise network or the Internet, this is the desired behavior as it allows firewall policy to be written to FTP/FTPS servers on well-known co
The overall behavior of the FTP ALG with the ftps-extensions option is intended behavior and will not change. The key component to this advisory is increasing user awareness of the wide TCP data channel (gate) creation, allowing creation of any new sessions from client to server, and potential implications where the SRX protects the FTPS server and the server/load-balancer allows the control channel to remain open for an extended period. Investigation into the issue identified two issues applicable to environments where the SRX protects both FTPS clients and servers, as well as uses FTP and FTPS over the same TCP ports to different servers. Due to the recent changes of OpenSSL, the FTP ALG without the ftps-extensions option may block FTPS commands over the FTP control channel. This is client and server specific, and was observed with FTPS clients that use recent versions of OpenSSL. This may result in security administrators enabling the ftps-extensions option with the intent of allowing the commands to pass, but inadvertently allowing wide gate creation. This was observed in a configuration with simultaneous FTPS client/server use, with use of the same ports for FTP and FTPS traffic. The ftps-extension option is not supported when the SRX performs a destination NAT of the FTPS server, as the ALG cannot inspect the control channel to modify the server’s IP address signaled to the client. In an environment of simultaneous FTP and FTPS server use with the ftps-extensions optio
Do not enable the 'ftps-extensions' option if FTPS is not needed. The 'ftps-extensions' option is disabled by default.
| Product | Vulnerable range | Fixed version | Advisory |
|---|---|---|---|
| n/a n/a | — | not specified | advisory ↗ |