From a4b5cfd34681ebf49370c27b3002782dec813482 Mon Sep 17 00:00:00 2001
From: Matteo Collina <hello@matteocollina.com>
Date: Fri, 9 Oct 2026 16:59:31 +0200
Subject: [PATCH] fix: reject chunked GET and HEAD bodies

---
 parser/fuzz/tests/conformance.rs    | 10 ++++++++++
 parser/src/parse.rs                 |  5 ++++-
 parser/tests/compliance.rs          | 17 +++++++++++++++++
 parser/wasm/test/compliance.test.js | 14 ++++++++++++++
 4 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/parser/fuzz/tests/conformance.rs b/parser/fuzz/tests/conformance.rs
index 6f4cf65..959ba38 100644
--- a/parser/fuzz/tests/conformance.rs
+++ b/parser/fuzz/tests/conformance.rs
@@ -57,6 +57,16 @@ fn rejects_transfer_encoding_not_ending_in_chunked() {
   }
 }
 
+#[test]
+fn rejects_chunked_get_and_head_requests() {
+  for input in [
+    &b"GET / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\n0\r\n\r\n"[..],
+    &b"HEAD / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\n1\r\nx\r\n0\r\n\r\n"[..],
+  ] {
+    assert_ne!(error_code(input, true), ERROR_NONE, "chunked GET/HEAD must be rejected: {input:?}");
+  }
+}
+
 // --- Well-formed messages must still be accepted. ---
 
 #[test]
diff --git a/parser/src/parse.rs b/parser/src/parse.rs
index 80105a0..bdb1bbc 100644
--- a/parser/src/parse.rs
+++ b/parser/src/parse.rs
@@ -836,7 +836,10 @@ impl Parser {
                 UNEXPECTED_TRAILERS,
                 "Trailers are not allowed when not using chunked transfer encoding"
               );
-            } else if self.is_request && (method == METHOD_GET || method == METHOD_HEAD) && self.content_length > 0 {
+            } else if self.is_request
+              && (method == METHOD_GET || method == METHOD_HEAD)
+              && (self.content_length > 0 || self.has_transfer_encoding)
+            {
               fail!(UNEXPECTED_CONTENT, "Unexpected content for the request (GET or HEAD)");
             }
 
diff --git a/parser/tests/compliance.rs b/parser/tests/compliance.rs
index fb1244a..e129465 100644
--- a/parser/tests/compliance.rs
+++ b/parser/tests/compliance.rs
@@ -196,6 +196,23 @@ fn compliance_head_body_rejected() {
   assert_error(&parser);
 }
 
+// Milo rejects chunked framing on GET and HEAD even when the encoded body is empty.
+#[test]
+fn compliance_get_head_chunked_body_rejected() {
+  for method in ["GET", "HEAD"] {
+    for body in ["0\r\n\r\n", "1\r\nx\r\n0\r\n\r\n"] {
+      let mut parser = request_parser();
+      let message = wire(&format!(
+        "{method} / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\n{body}"
+      ));
+
+      parse(&mut parser, &message);
+
+      assert_error(&parser);
+    }
+  }
+}
+
 // Methods other than GET and HEAD can carry valid body framing.
 #[test]
 fn compliance_post_body_accepted() {
diff --git a/parser/wasm/test/compliance.test.js b/parser/wasm/test/compliance.test.js
index a0cd1bf..e104ab8 100644
--- a/parser/wasm/test/compliance.test.js
+++ b/parser/wasm/test/compliance.test.js
@@ -131,6 +131,20 @@ it('compliance_head_body_rejected', t => {
   assertError(milo, parser)
 })
 
+// Milo rejects chunked framing on GET and HEAD even when the encoded body is empty.
+for (const method of ['GET', 'HEAD']) {
+  for (const [name, body] of [
+    ['empty', '0\r\n\r\n'],
+    ['non_empty', '1\r\nx\r\n0\r\n\r\n']
+  ]) {
+    it(`compliance_${method.toLowerCase()}_${name}_chunked_body_rejected`, t => {
+      const { milo, parser, parse } = requestParser(t)
+      parse(`${method} / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\n${body}`)
+      assertError(milo, parser)
+    })
+  }
+}
+
 // Methods other than GET and HEAD can carry valid body framing.
 it('compliance_post_body_accepted', t => {
   const { milo, parser, parse } = requestParser(t)