CVE-2024-30251: Aiohttp DoS Vulnerability via POST Request

CVE-2024-30251 Overview

CVE-2024-30251 is a Denial of Service (DoS) vulnerability in aiohttp, an asynchronous HTTP client/server framework for asyncio and Python. The vulnerability allows an attacker to send a specially crafted POST request with multipart/form-data content type that causes the aiohttp server to enter an infinite loop, rendering it completely unresponsive to any further requests.

Critical Impact
A single malicious request can completely disable an aiohttp-based web service, causing total application unavailability with no user interaction required.

Affected Products

aiohttp versions prior to 3.9.4
Applications using aiohttp server with multipart form data handling
Python asyncio-based web services leveraging the aiohttp framework

Discovery Timeline

2024-05-02 - CVE-2024-30251 published to NVD
2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-30251

Vulnerability Analysis

This vulnerability (CWE-835: Loop with Unreachable Exit Condition) exists in aiohttp's multipart form data parsing logic. When the server receives a specially crafted POST request with multipart/form-data content type, the parser enters an infinite loop condition where the exit criteria can never be satisfied. This is a classic algorithmic complexity attack where the attacker exploits improper boundary condition handling in the multipart parser.

The attack is particularly dangerous because it requires no authentication, can be executed remotely over the network, and completely halts all server functionality with just one request. The infinite loop consumes server resources indefinitely, preventing the processing of any legitimate requests until the service is manually restarted.

Root Cause

The root cause lies in improper handling of multipart form data boundaries within the aiohttp request parser. When malformed boundary delimiters or specially structured multipart content is sent to the server, the parsing loop fails to detect an exit condition, causing it to iterate indefinitely. The parser lacks proper validation checks to ensure that the loop will terminate under all input conditions.

Attack Vector

The attack vector is network-based and requires no privileges or user interaction. An attacker can exploit this vulnerability by sending a single HTTP POST request to any endpoint on the target aiohttp server that processes multipart/form-data requests. The attack can be executed remotely against any exposed aiohttp server instance.

The vulnerability is triggered during the processing of the malicious request, before any application-level logic is reached. This means that even properly secured endpoints with authentication are vulnerable if the server parses multipart data before authentication checks.

Detection Methods for CVE-2024-30251

Indicators of Compromise

Sudden complete unresponsiveness of aiohttp-based web services
Server process showing 100% CPU utilization with no request completion
Accumulated pending connections with no responses being sent
HTTP 503 or connection timeout errors reported by monitoring systems

Detection Strategies

Monitor for anomalous multipart/form-data POST requests with unusual boundary values or malformed content structures
Implement request timeout monitoring to detect requests that exceed normal processing times
Track CPU utilization spikes on servers running aiohttp applications
Set up health check endpoints with alerting on consecutive failures

Monitoring Recommendations

Deploy application performance monitoring (APM) to track request processing times and identify stuck requests
Configure network-level monitoring to detect POST requests to aiohttp servers with suspicious payload characteristics
Implement automated service restart mechanisms with alerting for aiohttp processes that become unresponsive

How to Mitigate CVE-2024-30251

Immediate Actions Required

Upgrade aiohttp to version 3.9.4 or later immediately
Review all applications using aiohttp to identify vulnerable deployments
Implement request timeout configurations at the reverse proxy or load balancer level as an additional defense layer
Consider deploying Web Application Firewall (WAF) rules to filter suspicious multipart requests

Patch Information

The aiohttp project has released version 3.9.4 which addresses this vulnerability. Multiple commits have been published to fix the issue:

For detailed patch instructions, refer to the GitHub Security Advisory GHSA-5m98-qgg9-wh84.

Workarounds

Users unable to upgrade can manually apply the patches from the linked commits to their aiohttp installation
Implement a reverse proxy (nginx, HAProxy) in front of aiohttp servers with strict request timeout limits
Configure rate limiting on endpoints that accept multipart form data
Restrict access to multipart form data endpoints to trusted sources where possible

bash

# Upgrade aiohttp to patched version
pip install --upgrade aiohttp>=3.9.4

# Verify the installed version
pip show aiohttp | grep Version