diff --git a/src/middleware/csrf.rs b/src/middleware/csrf.rs
new file mode 100644
index 00000000..5385f5d4
--- /dev/null
+++ b/src/middleware/csrf.rs
@@ -0,0 +1,266 @@
+//! A filter for cross-site request forgery (CSRF).
+//!
+//! This middleware is stateless and [based on request
+//! headers](https://www.owasp.org/index.php/Cross-Site_Request_Forgery_(CSRF)_Prevention_Cheat_Sheet#Verifying_Same_Origin_with_Standard_Headers).
+//!
+//! By default requests are allowed only if one of these is true:
+//!
+//! * The request method is safe (`GET`, `HEAD`, `OPTIONS`). It is the
+//! applications responsibility to ensure these methods cannot be used to
+//! execute unwanted actions. Note that upgrade requests for websockets are
+//! also considered safe.
+//! * The `Origin` header (added automatically by the browser) matches one
+//! of the allowed origins.
+//! * There is no `Origin` header but the `Referer` header matches one of
+//! the allowed origins.
+//!
+//! Use [`CsrfFilterBuilder::allow_xhr()`](struct.CsrfFilterBuilder.html#method.allow_xhr)
+//! if you want to allow requests with unsafe methods via
+//! [CORS](../cors/struct.Cors.html).
+//!
+//! # Example
+//!
+//! ```
+//! # extern crate actix_web;
+//! # use actix_web::*;
+//!
+//! use actix_web::middleware::csrf;
+//!
+//! fn handle_post(_req: HttpRequest) -> &'static str {
+//! "This action should only be triggered with requests from the same site"
+//! }
+//!
+//! fn main() {
+//! let app = Application::new()
+//! .middleware(
+//! csrf::CsrfFilter::build()
+//! .allowed_origin("https://www.example.com")
+//! .finish())
+//! .resource("/", |r| {
+//! r.method(Method::GET).f(|_| httpcodes::HttpOk);
+//! r.method(Method::POST).f(handle_post);
+//! })
+//! .finish();
+//! }
+//! ```
+//!
+//! In this example the entire application is protected from CSRF.
+
+use std::borrow::Cow;
+use std::collections::HashSet;
+
+use bytes::Bytes;
+use error::{Result, ResponseError};
+use http::{HeaderMap, HttpTryFrom, Uri, header};
+use httprequest::HttpRequest;
+use httpresponse::HttpResponse;
+use httpmessage::HttpMessage;
+use httpcodes::HttpForbidden;
+use middleware::{Middleware, Started};
+
+/// Potential cross-site request forgery detected.
+#[derive(Debug, Fail)]
+pub enum CsrfError {
+ /// The HTTP request header `Origin` was required but not provided.
+ #[fail(display="Origin header required")]
+ MissingOrigin,
+ /// The HTTP request header `Origin` could not be parsed correctly.
+ #[fail(display="Could not parse Origin header")]
+ BadOrigin,
+ /// The cross-site request was denied.
+ #[fail(display="Cross-site request denied")]
+ CsrDenied,
+}
+
+impl ResponseError for CsrfError {
+ fn error_response(&self) -> HttpResponse {
+ HttpForbidden.build().body(self.to_string()).unwrap()
+ }
+}
+
+fn uri_origin(uri: &Uri) -> Option<String> {
+ match (uri.scheme_part(), uri.host(), uri.port()) {
+ (Some(scheme), Some(host), Some(port)) => {
+ Some(format!("{}://{}:{}", scheme, host, port))
+ }
+ (Some(scheme), Some(host), None) => {
+ Some(format!("{}://{}", scheme, host))
+ }
+ _ => None
+ }
+}
+
+fn origin(headers: &HeaderMap) -> Option<Result<Cow<str>, CsrfError>> {
+ headers.get(header::ORIGIN)
+ .map(|origin| {
+ origin
+ .to_str()
+ .map_err(|_| CsrfError::BadOrigin)
+ .map(|o| o.into())
+ })
+ .or_else(|| {
+ headers.get(header::REFERER)
+ .map(|referer| {
+ Uri::try_from(Bytes::from(referer.as_bytes()))
+ .ok()
+ .as_ref()
+ .and_then(uri_origin)
+ .ok_or(CsrfError::BadOrigin)
+ .map(|o| o.into())
+ })
+ })
+}
+
+/// A middleware that filters cross-site requests.
+pub struct CsrfFilter {
+ origins: HashSet<String>,
+ allow_xhr: bool,
+ allow_missing_origin: bool,
+}
+
+impl CsrfFilter {
+ /// Start building a `CsrfFilter`.
+ pub fn build() -> CsrfFilterBuilder {
+ CsrfFilterBuilder {
+ cors: CsrfFilter {
+ origins: HashSet::new(),
+ allow_xhr: false,
+ allow_missing_origin: false,
+ }
+ }
+ }
+
+ fn validate<S>(&self, req: &mut HttpRequest<S>) -> Result<(), CsrfError> {
+ if req.method().is_safe() || (self.allow_xhr && req.headers().contains_key("x-requested-with")) {
+ Ok(())
+ } else if let Some(header) = origin(req.headers()) {
+ match header {
+ Ok(ref origin) if self.origins.contains(origin.as_ref()) => Ok(()),
+ Ok(_) => Err(CsrfError::CsrDenied),
+ Err(err) => Err(err),
+ }
+ } else if self.allow_missing_origin {
+ Ok(())
+ } else {
+ Err(CsrfError::MissingOrigin)
+ }
+ }
+}
+
+impl<S> Middleware<S> for CsrfFilter {
+ fn start(&self, req: &mut HttpRequest<S>) -> Result<Started> {
+ self.validate(req)?;
+ Ok(Started::Done)
+ }
+}
+
+/// Used to build a `CsrfFilter`.
+///
+/// To construct a CSRF filter:
+///
+/// 1. Call [`CsrfFilter::build`](struct.CsrfFilter.html#method.build) to
+/// start building.
+/// 2. [Add](struct.CsrfFilterBuilder.html#method.allowed_origin) allowed
+/// origins.
+/// 3. Call [finish](struct.CsrfFilterBuilder.html#method.finish) to retrieve
+/// the constructed filter.
+///
+/// # Example
+///
+/// ```
+/// use actix_web::middleware::csrf;
+///
+/// let csrf = csrf::CsrfFilter::build()
+/// .allowed_origin("https://www.example.com")
+/// .finish();
+/// ```
+pub struct CsrfFilterBuilder {
+ cors: CsrfFilter,
+}
+
+impl CsrfFilterBuilder {
+ /// Add an origin that is allowed to make requests. Will be verified
+ /// against the `Origin` request header.
+ pub fn allowed_origin(mut self, origin: &str) -> CsrfFilterBuilder {
+ self.cors.origins.insert(origin.to_owned());
+ self
+ }
+
+ /// Allow all requests with an `X-Requested-With` header.
+ ///
+ /// A cross-site attacker should not be able to send requests with custom
+ /// headers unless a CORS policy whitelists them. Therefore it should be
+ /// safe to allow requests with an `X-Requested-With` header (added
+ /// automatically by many JavaScript libraries).
+ ///
+ /// This is disabled by default, because in Safari it is possible to
+ /// circumvent this using redirects and Flash.
+ ///
+ /// Use this method to enable more lax filtering.
+ pub fn allow_xhr(mut self) -> CsrfFilterBuilder {
+ self.cors.allow_xhr = true;
+ self
+ }
+
+ /// Allow requests if the expected `Origin` header is missing (and
+ /// there is no `Referer` to fall back on).
+ ///
+ /// The filter is conservative by default, but it should be safe to allow
+ /// missing `Origin` headers because a cross-site attacker cannot prevent
+ /// the browser from sending `Origin` on unsafe requests.
+ pub fn allow_missing_origin(mut self) -> CsrfFilterBuilder {
+ self.cors.allow_missing_origin = true;
+ self
+ }
+
+ /// Finishes building the `CsrfFilter` instance.
+ pub fn finish(self) -> CsrfFilter {
+ self.cors
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+ use http::Method;
+ use test::TestRequest;
+
+ #[test]
+ fn test_safe() {
+ let csrf = CsrfFilter::build()
+ .allowed_origin("https://www.example.com")
+ .finish();
+
+ let mut req = TestRequest::with_header("Origin", "https://www.w3.org")
+ .method(Method::HEAD)
+ .finish();
+
+ assert!(csrf.start(&mut req).is_ok());
+ }
+
+ #[test]
+ fn test_csrf() {
+ let csrf = CsrfFilter::build()
+ .allowed_origin("https://www.example.com")
+ .finish();
+
+ let mut req = TestRequest::with_header("Origin", "https://www.w3.org")
+ .method(Method::POST)
+ .finish();
+
+ assert!(csrf.start(&mut req).is_err());
+ }
+
+ #[test]
+ fn test_referer() {
+ let csrf = CsrfFilter::build()
+ .allowed_origin("https://www.example.com")
+ .finish();
+
+ let mut req = TestRequest::with_header("Referer", "https://www.example.com/some/path?query=param")
+ .method(Method::POST)
+ .finish();
+
+ assert!(csrf.start(&mut req).is_ok());
+ }
+}
diff --git a/src/middleware/mod.rs b/src/middleware/mod.rs
index 4270c477..cfda04b9 100644
--- a/src/middleware/mod.rs
+++ b/src/middleware/mod.rs
@@ -9,6 +9,7 @@ mod logger;
mod session;
mod defaultheaders;
pub mod cors;
+pub mod csrf;
pub use self::logger::Logger;
pub use self::defaultheaders::{DefaultHeaders, DefaultHeadersBuilder};
pub use self::session::{RequestSession, Session, SessionImpl, SessionBackend, SessionStorage,