CVE-2021-21299: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') (CWE-444)
value: hyper is an open-source HTTP library for Rust (crates.io). In hyper from version 0.12.0 and before versions 0.13.10 and 0.14.3 there is a vulnerability that can enable a request smuggling attack. The HTTP server code had a flaw that incorrectly understands some requests with multiple transfer-encoding headers to have a chunked payload, when it should have been rejected as illegal. This combined with an upstream HTTP proxy that understands the request payload boundary differently can result in "request smuggling" or "desync attacks". To determine if vulnerable, all these things must be true: 1) Using hyper as an HTTP server (the client is not affected), 2) Using HTTP/1.1 (HTTP/2 does not use transfer-encoding), 3) Using a vulnerable HTTP proxy upstream to hyper. If an upstream proxy correctly rejects the illegal transfer-encoding headers, the desync attack cannot succeed. If there is no proxy upstream of hyper, hyper cannot start the desync attack, as the client will repair the headers before forwarding. This is fixed in versions 0.14.3 and 0.13.10. As a workaround one can take the following options: 1) Reject requests that contain a `transfer-encoding` header, 2) Ensure any upstream proxy handles `transfer-encoding` correctly.
CWE description: The product acts as an intermediary HTTP agent
         (such as a proxy or firewall) in the data flow between two
         entities such as a client and server, but it does not
         interpret malformed HTTP requests or responses in ways that
         are consistent with how the messages will be processed by
         those entities that are at the ultimate destination.
CVSS v3 base score: 8.1
Published: 2021-02-11T18:15Z
Repository: https://github.com/hyperium/hyper
Language: Rust
Files changed: src/proto/h1/role.rs
Commit date: 2021-02-05 14:10:02 -0800
Commit message: fix(http1): fix server misinterpretting multiple Transfer-Encoding headers

When a request arrived with multiple `Transfer-Encoding` headers, hyper
would check each if they ended with `chunked`. It should have only
checked if the *last* header ended with `chunked`.

See https://github.com/hyperium/hyper/security/advisories/GHSA-6hfq-h8hq-87mf

Diff: diff --git a/src/proto/h1/role.rs b/src/proto/h1/role.rs
index 0c7eb1e..a9f2f00 100644
--- a/src/proto/h1/role.rs
+++ b/src/proto/h1/role.rs
@@ -211,10 +211,12 @@ impl Http1Transaction for Server {
                     }
                     is_te = true;
                     if headers::is_chunked_(&value) {
                         is_te_chunked = true;
                         decoder = DecodedLength::CHUNKED;
+                    } else {
+                        is_te_chunked = false;
                     }
                 }
                 header::CONTENT_LENGTH => {
                     if is_te {
                         continue;
@@ -1442,10 +1444,20 @@ mod tests {
              \r\n\
              ",
             "transfer-encoding doesn't end in chunked",
         );
 
+        parse_err(
+            "\
+             POST / HTTP/1.1\r\n\
+             transfer-encoding: chunked\r\n\
+             transfer-encoding: afterlol\r\n\
+             \r\n\
+             ",
+            "transfer-encoding multiple lines doesn't end in chunked",
+        );
+
         // http/1.0
 
         assert_eq!(
             parse(
                 "\

Fixed code:                     } else {
                        is_te_chunked = false;
        parse_err(
            "\
             POST / HTTP/1.1\r\n\
             transfer-encoding: chunked\r\n\
             transfer-encoding: afterlol\r\n\
             \r\n\
             ",
            "transfer-encoding multiple lines doesn't end in chunked",
        );