About web shell scan

Web shell scan is a cross platform standalone binary that recursively scans through a specified directory with either user defined or default regex. Web shell scan utilizes a pool of go routines (10 total) to read from a channel and speed up the scanner. Note, the regex supplied with the scanner isn't 100% and does not guarantee it will find every web shell on disk.

This tool is related to the following write up:

https://blog.stillztech.com/2018/08/analyzing-and-detecting-web-shells.html

To test effectiveness of the scanner, it was tested against the tennc web shell repo:

https://github.com/tennc/webshell

Requirements

None! Simply download the binary for your OS, supply the directory you wish to scan and let it rip.

Running the binary

Running webscan with no arguments shows the following arguments:

/Users/beastmode$ ./webscan
Options:
    -dir string
      	Directory to scan for web shells
    -exts string
      	Specify extensions to target. Multiple extensions should be passed with pipe separator (asp|aspx|php|cfm). Default is all extensions
    -raw_contents
      	If a match is found, grab the raw contents and base64 + gzip compress the file into the JSON object.
    -regex string
      	Override default regex with your own
    -size int
      	Specify max file size to scan (default is 10 MB) (default 10)

The only required argument is dir, but you can override the program defaults if you wish.

The output of the scan will be written to console. Example below (For best results, send stdout to a json file and review/post process offline):

/Users/beastmode$ ./webscan -dir /Users/beastmode/webshell-master

{"filePath":"/Users/beastmode/webshell-master/xakep-shells/PHP/wacking.php.php.txt","size":142739,"md5":"9c5bb5e3a46ec28039e8986324e42792","timestamps":{"birth":"2019-02-03 02:02:22","created":"2019-03-17 13:18:52","modified":"2019-02-03 02:02:22","accessed":"2019-04-25 01:19:47"},"matches":{"eval(":2}}

### With STDOUT:

/Users/beastmode$ ./webscan -dir /Users/beastmode/webshell-master -raw_contents=true > scan_results.json

Once the scanner finishes, it will output the overall scan metrics to STDOUT, as shown in the example below:

{"scanned":1575,"matches":501,"noMatches":1074,"directory":"/Users/beastmode$/Downloads/webshell-master","scanDuration":1.2528534718166666,
"systemInfo":{"hostname":"beastmode","envVars":["...."],"username":"beastmode","userID":"12345","realName":"","userHomeDir":"/Users/beastmode"}}

Custom regex

You can also supply your own regex if you have some specific regex pattern you're looking for:

./webscan -dir=/opt/https -regex="eval\\(|cmd|exec\\(" -size=5 -raw_contents=true -exts=php|jsp

Building the project

If you decide to modify the source code, you can build the project using the following commands:

cd <path-to-project>
## Windows
GOOS=windows GOARCH=386 go build -o webscan_windows.exe main.go
## Linux
GOOS=linux GOARCH=386 go build -o webscan_linux main.go
## Darwin
GOOS=darwin GOARCH=386 go build -o webscan_darwin main.go