CVE-2024-30251 – This vulnerability in aiohttp allows an attacke... (How to Fix)

📋 TL;DR

This vulnerability in aiohttp allows an attacker to send a specially crafted multipart/form-data POST request that causes the server to enter an infinite loop, making it unresponsive to further requests. All aiohttp servers running affected versions are vulnerable. This is a denial-of-service attack that requires only a single malicious request.

💻 Affected Systems

Products:

aiohttp

Versions: Versions before 3.9.4

Operating Systems: All operating systems running Python

Default Config Vulnerable: ⚠️ Yes

Notes: Any aiohttp server accepting POST requests with multipart/form-data is vulnerable. The vulnerability is in the request parsing logic.

📦 What is this software?

Aiohttp by Aiohttp

View all CVEs affecting Aiohttp →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete service outage where the aiohttp server becomes completely unresponsive, requiring manual restart and causing extended downtime.

🟠

Likely Case

Targeted denial-of-service against specific aiohttp endpoints, making affected services unavailable until the server is restarted.

🟢

If Mitigated

Limited impact with proper monitoring and automated restart mechanisms in place, though service interruptions may still occur.

🌐 Internet-Facing: HIGH - Internet-facing aiohttp servers are directly exposed to this attack from any source.

🏢 Internal Only: MEDIUM - Internal servers are still vulnerable but require attacker access to internal network.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

The exploit requires sending a specially crafted HTTP request but no authentication or special privileges. Proof of concept details are available in the security advisory.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 3.9.4

Vendor Advisory: https://github.com/aio-libs/aiohttp/security/advisories/GHSA-5m98-qgg9-wh84

Restart Required: Yes

Instructions:

1. Upgrade aiohttp to version 3.9.4 or later using pip: pip install --upgrade aiohttp>=3.9.4
2. Restart all aiohttp server processes
3. Verify the upgrade was successful

🔧 Temporary Workarounds

Request filtering with reverse proxy

all

Configure a reverse proxy (nginx, Apache) to filter or block suspicious multipart/form-data requests before they reach the aiohttp server.

Rate limiting

all

Implement rate limiting on POST endpoints to limit the impact of repeated attack attempts.

🧯 If You Can't Patch

Implement WAF rules to detect and block the specific multipart/form-data pattern that triggers the infinite loop
Deploy monitoring with automated restart for aiohttp processes that become unresponsive

🔍 How to Verify

Check if Vulnerable:

Check aiohttp version: python -c "import aiohttp; print(aiohttp.__version__)" - if version is less than 3.9.4, the system is vulnerable.

Check Version:

python -c "import aiohttp; print('aiohttp version:', aiohttp.__version__)"

Verify Fix Applied:

After upgrade, verify version is 3.9.4 or higher and test that multipart/form-data requests process normally without hanging.

📡 Detection & Monitoring

Log Indicators:

A single POST request followed by server becoming unresponsive
Increased CPU usage without corresponding request processing
Timeout errors from clients

Network Indicators:

Single POST request with multipart/form-data content-type causing server to stop responding
Sudden drop in successful HTTP responses after specific POST request

SIEM Query:

source="aiohttp" AND (http_method="POST" AND content_type="multipart/form-data") FOLLOWED BY (response_time>30s OR no_response)

📊 Metadata

CVE ID: CVE-2024-30251

CVSS v3 Score: 7.5 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE: CWE-835

Published: May 2, 2024

Last Updated: November 3, 2025

🔗 References

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