13 practical tips for writing secure golang applications

13 Go security tips Karthik 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

“Iron.io: How We Went from 30 Servers to 2 d n a o G h t with Go” i w s c i s y h p b e W f o s w a l n i e l o h s w o l ” b n u e r g l i a l a F R d u o l C “ “Why you PHP guys should learn Golang” “Why I went from Python to Go (and not node.js)” “Go is awesome” “I have now comp leted two pro jects in Go. I going to be predict that i the dominan t’s t language fo r server work .” “Prediction: Go will become the dominant language for systems work in IaaS, Orchestration, and PaaS in 24 months.” “Another go at the Next Big Language” Source

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=="; pinsha256="base64+backup=="; max-age=5184000; includeSubdomains; reporturi="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

var 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> nosurf example 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-yourdevelopment-team-started-with-go/ • https://github.com/astaxie/build-web-application-with-golang • https://speakerdeck.com/ngalbreath/secure-applicationdevelopment-with-golang

Thanks!