13 practical tips for writing secure golang applications

13 Go security tipsKarthik Gaekwad - @iteration1

I’m Karthik @iteration1

I speak docker golang

History of Go• “Go is an open source programming language that makes it

easy to build simple, reliable, and efficient software.”

• Almost 6 years old (November 10th).

• Born after looking at hairy C++ code.

• Current: Go 1.5

• Over 200 companies use go

• ~1200 people @gophercon

• Great for webapps/devops/server mgmt

“Go is awesome”

“Iron.io: How We Went from 30 Servers to 2 with Go”

“Another go at the Next Big Language”

“CloudFlare blows hole in laws of Web physics with Go and

Railgun”

"I have now completed two projects in Go. I predict that it's going to be the dominant language for server work."

Source

“Why I went from Python to Go (and not node.js)”“Why you PHP guys should learn Golang”

"Prediction: Go will become the dominant language for systems work in IaaS, Orchestration, and

PaaS in 24 months."

Pwnage?Does anyone care?

Is there a security policy?https://golang.org/security#tmp_1

Vulnerability List

https://www.cvedetails.com/vendor/14185/Golang.html

Okay, so it’s not all bad news…

Features!

Go is strongly-typed

• The type of every object is known at runtime.

• This cannot be changed.

• Pointers exist, but pointer arithmetic does not.

Memory Managed

• Garbage collector FTW.

• Accessing out of bound indexes in arrays ends with a hard panic.

• Once again, no pointer arithmetic:: can’t create buffer overflows.

Gofmt

• Source code formatter.

• Spend time writing code, not formatting it.

• Integrated with editors (vim/sublimetext/eclipse etc)

• Untweakable!

Gofmt motivation

• Code Reviews

• A Best Practice but….

• “Too much time lost on reviewing formatting rather than code.”

https://talks.go-zh.org/2015/gofmt-en.slide

Other tooling• golint

• Code linter.

• Finds common lint issues or things that don’t belong to a standard.

• Could add this to your CI pipeline, but is volatile.

• go vet

• Looks for weird constructs in your code.

• Examples: Useless assignments, incorrect printf format, unreachable code

• Good list of tools to review: http://dominik.honnef.co/posts/2014/12/an_incomplete_list_of_go_tools/

Standard Packages ftw• Standard libs have pretty good support for most things

you need.

• Don’t have to search for 3rd party libs first…

• All crypto algorithms are in packages under the crypto package.

• crypto.random uses /dev/urandom by default

• good read: https://leanpub.com/gocrypto (Kyle Isom)

Single Binary

• Statically linked, so everything you need is in your binary.

• Helps with product distribution.

• Reduces burden with installation issues on client host.

App Dependencies• Package management:

• Keeps team on the same page.

• Reproducible builds.

• Godep:

• Most popular

• Code is vendorized.

• All your dependencies live inside your application.

• Sorta like (java) ant, but with the source.

Web Application Building• Easy to build your own HTTP/HTTPS server

Web Applications: XSS

• Go Templates- html/template and text/template:

• You want to use html/template for your webapps.

• html/template package escapes all html tags! (template.HTMLEscape or ExecuteTemplate).

• text/template does not!!

Gorilla toolkit

• Awesome toolkit for writing web applications.

• Assists with writing more secure code when you don’t know how to code.

• Gorilla toolkit >>> roll your own

• http://www.gorillatoolkit.org/

Gorilla toolkit• gorilla/securecookie

• Secure cookie: Encodes/Decodes cookie values for you.

• Value is validated with HMAC.

• Add encryption, and content is inaccessible to end user.

• gorilla/sessions

• Simple API for signed (and encrypted) cookies.

• Clean mechanism to rotate session authentication and encryption keys.

• gorilla/mux: Great for routing web apps

• Also gorilla/context, gorilla/websockets and a few others

c’mon man

Secure middleware• https://github.com/unrolled/secure

• Middleware that helps you with some quick security wins.

• + XSS Protection headers

• + CSP headers

• + SSL Check/SSL Redirects

Example: secureMiddleware := secure.New(secure.Options{ AllowedHosts: []string{"example.com", "ssl.example.com"}, SSLRedirect: true, SSLHost: "ssl.example.com", SSLProxyHeaders: map[string]string{"X-Forwarded-Proto": "https"}, STSSeconds: 315360000, STSIncludeSubdomains: true, STSPreload: true, FrameDeny: true, ContentTypeNosniff: true, BrowserXssFilter: true, ContentSecurityPolicy: "default-src 'self'", PublicKey: `pin-sha256="base64+primary=="; pin-sha256="base64+backup=="; max-age=5184000; includeSubdomains; report-uri="https://www.example.com/hpkp-report"`, })

CSRF• nosurf is an HTTP package that helps with

prevention of cross site request forgery.

• https://github.com/justinas/nosurf

nosurf examplevar templateString = ` <!doctype html> <html><body> {{ if .name }} <p>Your name: {{ .name }}</p> {{ end }} <form action="/" method="POST"> <input type="text" name="name"> <!-- Try removing this or changing its value and see what happens --> <input type="hidden" name="csrf_token" value="{{ .token }}"><input type="submit" value="Send"> </form></body></html> `

var templ = template.Must(template.New("t1").Parse(templateString))

func myFunc(w http.ResponseWriter, r *http.Request) { context := make(map[string]string) context["token"] = nosurf.Token(r)

if r.Method == "POST" { context["name"] = r.FormValue("name") }

templ.Execute(w, context) }

func main() { myHandler := http.HandlerFunc(myFunc) fmt.Println("Listening on http://127.0.0.1:8000/") http.ListenAndServe(":8000", nosurf.New(myHandler)) }

SQL Injections• Same as other languages…..

username := r.Form.Get("username") password := r.Form.Get(“password")

// Oh noes!! sql := "SELECT * FROM user WHERE username='" + username + "' AND password='" + password + “'" Db.Exec(sql)

// Oh yes!! sql := "SELECT * FROM user WHERE username=? AND password=?” Db.Exec(sql, username, password)

SQL Injections• Limit DB user permissions so that the impact is minimal.

• Sanitize inputs, escape special characters (‘“\&*;).

• Use the HTMLEscapeString for this.

• Use parameterized queries!

• Code review DB.exec so that you’re using the parameterized query interface.

• Or use Query/Prepare instead.

• Run your code against sqlmap or gauntlt.

Friends who Go!

This could be you

More resources• Austin Golang meetup (@Umbel downtown)

• https://golang.org/doc/

• https://golang.org/doc/code.html

• https://www.digitalocean.com/company/blog/get-your-development-team-started-with-go/

• https://github.com/astaxie/build-web-application-with-golang

• https://speakerdeck.com/ngalbreath/secure-application-development-with-golang

Thanks!