Gokart – A Static Analysis Tool For Securing Go Code

GoKart is a static analysis tool for Go that finds vulnerabilities using the SSA (single static assignment) form of Go source code. It is capable of tracing the source of variables and function arguments to determine whether input sources are safe, which reduces the number of false positives compared to other Go security scanners. For instance, a SQL query that is concatenated with a variable might traditionally be flagged as SQL injection; however, GoKart can figure out if the variable is actually a constant or constant equivalent, in which case there is no vulnerability.

Why We Built GoKart

Static analysis is a powerful technique for finding vulnerabilities in source code. However, the approach has suffered from being noisy – that is, many static analysis tools find quite a few “vulnerabilities” that are not actually real. This has led to developer friction as users get tired of the tools “crying wolf” one time too many.

The motivation for GoKart was to address this: could we create a scanner with significantly lower false positive rates than existing tools? Based on our experimentation the answer is yes. By leveraging source-to-sink tracing and SSA, GoKart is capable of tracking variable taint between variable assignments, significantly improving the accuracy of findings. Our focus is on usability: pragmatically, that means we have optimized our approaches to reduce false alarms.

For more information, please read our blog post.

Install

You can install GoKart locally by using any one of the options listed below.

Install with go install

$ go install github.com/praetorian-inc/gokart@latest

Install a release binary

1. Download the binary for your OS from the releases page.

2. (OPTIONAL) Download the checksums.txt file to verify the integrity of the archive

# Check the checksum of the downloaded archive
$ shasum -a 256 gokart_${VERSION}_${ARCH}.tar.gz
b05c4d7895be260aa16336f29249c50b84897dab90e1221c9e96af9233751f22  gokart_${VERSION}_${ARCH}.tar.gz

$ cat gokart_${VERSION}_${ARCH}_checksums.txt | grep gokart_${VERSION}_${ARCH}.tar.gz
b05c4d7895be260aa16336f29249c50b84897dab90e1221c9e96af9233751f22  gokart_${VERSION}_${ARCH}.tar.gz

3. Extract the downloaded archive

$ tar -xvf gokart_${VERSION}_${ARCH}.tar.gz

4. Move the gokart binary into your path:

$ mv ./gokart /usr/local/bin/

Clone and build yourself

# clone the GoKart repo
$ git clone https://github.com/praetorian-inc/gokart.git

# navigate into the repo directory and build
$ cd gokart
$ go build

# Move the gokart binary into your path
$ mv ./gokart /usr/local/bin

Usage

Run GoKart on a Go module in the current directory

# running without a directory specified defaults to '.'
gokart scan <flags>

Scan a Go module in a different directory

gokart scan <directory> <flags> 

Get Help

gokart help

Getting Started – Scanning an Example App

You can follow the steps below to run GoKart on Go Test Bench, an intentionally vulnerable Go application from the Contrast Security team.

# Clone sample vulnerable application
git clone https://github.com/Contrast-Security-OSS/go-test-bench.git
gokart scan go-test-bench/

Output should show some identified vulnerabilities, each with a Vulnerable Function and Source of User Input identified.

To test some additional GoKart features, you can scan with the CLI flags suggested below.

# Use verbose flag to show full traces of these vulnerabilities
gokart scan go-test-bench/ -v

# Use globalsTainted flag to ignore whitelisted Sources
# may increase false positive results
gokart scan go-test-bench/ -v -g

# Use debug flag to display internal analysis information
# which is useful for development and debugging
gokart scan go-test-bench/ -d

# Output results in sarif format
gokart scan go-test-bench/ -s

# Output results to file
gokart scan go-test-bench/ -o gokart-go-test-bench.txt

# Output scarif results to file
gokart scan go-test-bench/ -o gokart-go-test-bench.txt -s

# Scan remote repository (private repos require proper authentication)
# Repository will be cloned locally, scanned and deleted afterwards
gokart scan -r github.com/ShiftLeftSecurity/shiftleft-go-demo -v

# Use remote scan and output flags together for seamless security reviews
gokart sca   n -r github.com/ShiftLeftSecurity/shiftleft-go-demo -o gokart-shiftleft-go-demo.txt -v 

# Use remote scan, output and sarif flags for frictionless integration into CI/CD
gokart scan -r github.com/ShiftLeftSecurity/shiftleft-go-demo -o gokart-shiftleft-go-demo.txt -s

To test out the extensibility of GoKart, you can modify the configuration file that GoKart uses to introduce a new vulnerable sink into analysis. There is a Test Sink analyzer defined in the included default config file at util/analyzers.yml. Modify util/analyzers.yml to remove the comments on the Test Sink analyzer and then direct GoKart to use the modified config file with the -i flag.

# Scan using modified analyzers.yml file and output full traces
gokart scan go-test-bench/ -v -i <path-to-gokart>/util/analyzers.yml

Output should now contain additional vulnerabilities, including new “Test Sink reachable by user input” vulnerabilities.

Run GoKart Tests

You can run the included tests with the following command, invoked from the GoKart root directory.

go test -v ./...