reject %2F in url paths

actix-files/CHANGES.md

@@ -1,7 +1,7 @@
 # Changes
 
 ## Unreleased - 2021-xx-xx
-- `Files`: `%2F` in request URL path is now decoded to `/` and thus functions as a path separator. [#2398]
+- `Files`: request URL paths with `%2F` are now rejected. [#2398]
 - `Files`: Fixed a regression where `%25` in the URL path is not decoded to `%` in the file path. [#2398]
 - Minimum supported Rust version (MSRV) is now 1.54.
 

actix-files/src/error.rs

@@ -23,16 +23,20 @@ impl ResponseError for FilesError {
 
 #[allow(clippy::enum_variant_names)]
 #[derive(Display, Debug, PartialEq)]
+#[non_exhaustive]
 pub enum UriSegmentError {
     /// The segment started with the wrapped invalid character.
     #[display(fmt = "The segment started with the wrapped invalid character")]
     BadStart(char),
+
     /// The segment contained the wrapped invalid character.
     #[display(fmt = "The segment contained the wrapped invalid character")]
     BadChar(char),
+
     /// The segment ended with the wrapped invalid character.
     #[display(fmt = "The segment ended with the wrapped invalid character")]
     BadEnd(char),
+
     /// The path is not a valid UTF-8 string after doing percent decoding.
     #[display(fmt = "The path is not a valif UTF-8 string after percent-decoding")]
     NotValidUtf8,

actix-files/src/files.rs

@@ -28,16 +28,6 @@ use crate::{
 ///
 /// `Files` service must be registered with `App::service()` method.
 ///
-/// # Percent-Encoding and Security Considerations
-///
-/// When converting the request URL path into the target [file path](std::path::Path),
-/// `Files` service *does* decode *all* percent-encoded characters in the path string.
-/// One implication is that the resulting file path may have more components than the URL path
-/// as a result of decoding `%2F` into `/`.
-///
-/// Any middleware that is responsible for validating the paths managed under `Files`
-/// should be aware of this behavior.
-///
 /// # Examples
 /// ```
 /// use actix_web::App;

actix-files/src/lib.rs

@@ -805,11 +805,9 @@ mod tests {
         assert_eq!(res.status(), StatusCode::OK);
 
         // `%2F` == `/`
-        let req = TestRequest::get()
+        let req = TestRequest::get().uri("/test%2Ftest.binary").to_request();
-            .uri("/test/%2F..%2F..%2Ftests%2Ftest.binary")
-            .to_request();
         let res = test::call_service(&srv, req).await;
-        assert_eq!(res.status(), StatusCode::OK);
+        assert_eq!(res.status(), StatusCode::NOT_FOUND);
 
         let req = TestRequest::get().uri("/test/Cargo.toml%00").to_request();
         let res = test::call_service(&srv, req).await;

actix-files/src/path_buf.rs

@@ -1,5 +1,5 @@
 use std::{
-    path::{Path, PathBuf},
+    path::{Component, Path, PathBuf},
     str::FromStr,
 };
 
@@ -26,12 +26,21 @@ impl PathBufWrap {
     pub fn parse_path(path: &str, hidden_files: bool) -> Result<Self, UriSegmentError> {
         let mut buf = PathBuf::new();
 
+        // equivalent to `path.split('/').count()`
+        let mut segment_count = path.matches('/').count() + 1;
+
         let path = percent_encoding::percent_decode_str(path)
             .decode_utf8()
             .map_err(|_| UriSegmentError::NotValidUtf8)?;
 
+        // disallow decoding `%2F` into `/`
+        if segment_count != path.matches('/').count() + 1 {
+            return Err(UriSegmentError::BadChar('/'));
+        }
+
         for segment in path.split('/') {
             if segment == ".." {
+                segment_count -= 1;
                 buf.pop();
             } else if !hidden_files && segment.starts_with('.') {
                 return Err(UriSegmentError::BadStart('.'));
@@ -44,6 +53,7 @@ impl PathBufWrap {
             } else if segment.ends_with('<') {
                 return Err(UriSegmentError::BadEnd('<'));
             } else if segment.is_empty() {
+                segment_count -= 1;
                 continue;
             } else if cfg!(windows) && segment.contains('\\') {
                 return Err(UriSegmentError::BadChar('\\'));
@@ -52,6 +62,12 @@ impl PathBufWrap {
             }
         }
 
+        // make sure we agree with stdlib parser
+        for (i, component) in buf.components().enumerate() {
+            assert!(matches!(component, Component::Normal(_)));
+            assert!(i < segment_count);
+        }
+
         Ok(PathBufWrap(buf))
     }
 }