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webshell-cli Specification

This document specifies the requirements a webshell needs to implement to be compatible with webshell-cli.

pattern

webshell-cli includes a parameter within name pattern in each request. The webshell on the server side is expected to return the result of a webshell-cli call enclosed within this pattern (<pattern><result><pattern>). This allows webshell-cli to find the shell output, even if other data is contained within the response.

chdir

Requests dispatched by webshell-cli can generally contain the chdir parameter. If the parameter was specified, it contains a base64 encoded file system path. Webshells need to verify whether this path is accessible and return a 202 status code if this is not the case. The corresponding HTTP response should contain a base64 encoded reason, why the change was not possible or at least a generic error message.

b64_env

Requests dispatched by webshell-cli can generally contain the b64_env parameter. If the parameter was specified, it contains base64 encoded environment variable pairs, each separated by :. The pairs itself are of the format key=value.

Responses

HTTP responses for webshell-cli are usually base64 encoded. If multiple values need to be returned, their base64 contents are separated by a colon. Each successful server response should contain the currently active path as the last item. This should be the path that results after the chdir parameter was applied. This is used to get the actual names of client specified paths like: .. The server response should return the resolved path in this case.

Actions

webshell-cli uses the action parameter to instruct the webshell what kind of operation it should perform. The action is passed as a plain string and does not need to be specified. The following values for the action parameter are possible:

init

Available parameters:

  • action - set to init

The init action is used by webshell-cli to obtain some general information about the application server. The webshell needs to respond with the following base64 encoded items, all separated by a colon:

  • The directory separator used by the system
  • The webshell type (e.g. PHP or JSP)
  • The associated user name of the current process
  • The hostname of the application server

cmd

Available parameters:

  • action - set to cmd
  • b64_cmd - contains the base64 encoded command
  • back - boolean. Specifies whether the command is executed as background command
  • chdir - directory to execute the command in
  • b64_env - environment to use during the command execution

The cmd action is specified together with the b64_cmd parameter, which contains a base64 encoded command that should be executed. During execution, the webshell should respect the current chdir and b64_env settings. The output of the command should be returned as base64.

eval

Available parameters:

  • action - set to eval
  • chdir - directory to evaluate in
  • b64_env - environment to use during evaluation
  • b64_upload - content to evaluate on the server side

If the eval action was used, the request also contains the b64_upload parameter that contains the contents of a file that should be evaluated. Whether this is possible depends on the server-side webshell technology. So far, this function is only implemented for the PHP webshell. This action should return no response (apart from the cwd response mentioned above).

upload

Available parameters:

  • action - set to upload
  • chdir - current directory specification
  • b64_orig - the original filename of the file being uploaded
  • b64_upload - the file content to be uploaded
  • b64_filename - the filename to upload to

When the upload action is used, the parameter b64_upload contains the base64 encoded contents of a file that should be uploaded. The parameter b64_filename contains a base64 encoded desired filename, where the file should be saved. If the targeted filename is a directory, webshells should use the b64_orig parameter that contains the base64 encoded original name of the file to upload. The webshell should save the file under this name in the directory specified by b64_filename. This action should return no response (apart from the cwd response mentioned above).

download

Available parameters:

  • action - set to download
  • chdir - current directory specification
  • b64_filename - the filename to download

When the download action is used, the parameter b64_filename contains the base64 encoded name of a file that should be downloaded. The server should simply return the content of the file as base64.