CVE-2025-69228: AIOHTTP DOS Vulnerability

CVE-2025-69228 Overview

CVE-2025-69228 is a memory exhaustion vulnerability affecting AIOHTTP, an asynchronous HTTP client/server framework for asyncio and Python. Versions 3.13.2 and below contain a flaw that allows attackers to craft malicious requests that cause uncontrolled memory consumption during processing, potentially leading to server freeze or crash.

Critical Impact

Attackers can exploit the Request.post() method to exhaust server memory, causing denial of service conditions that freeze affected AIOHTTP applications.

Affected Products

• AIOHTTP versions 3.13.2 and earlier
• Python applications using AIOHTTP with handlers that implement Request.post() method
• Web servers and API services built on the AIOHTTP framework

Discovery Timeline

• 2026-01-06 - CVE-2025-69228 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2025-69228

Vulnerability Analysis

This vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling). The core issue stems from improper enforcement of the client_max_size limit when processing multipart form data. Prior to the fix, the size counter was reset for each field in a multipart request rather than accumulating across the entire form submission. This design flaw allows an attacker to bypass the intended upload size restrictions by splitting a large payload across multiple multipart fields, with each field individually staying under the limit while the total payload grows unbounded.

The vulnerability specifically affects applications that expose handlers using the Request.post() method to process incoming form data. Since AIOHTTP is widely used for building asynchronous web applications and APIs in Python, this memory exhaustion issue presents a significant availability risk for affected deployments.

Root Cause

The root cause lies in the multipart form processing logic within aiohttp/web_request.py. The size tracking variable was initialized inside the loop that iterates over multipart fields, causing it to reset to zero for each new field. This prevented the framework from properly accumulating the total size of all fields and enforcing the configured client_max_size limit across the entire multipart request.

Attack Vector

The attack leverages the network-accessible nature of AIOHTTP web servers. An unauthenticated remote attacker can craft a multipart HTTP request containing numerous small fields that individually pass size validation but collectively consume excessive memory. By repeatedly submitting such requests, or by sending requests with many fields, the attacker can exhaust available server memory without requiring any special privileges or user interaction.

             multipart = await self.multipart()
             max_size = self._client_max_size
 
+            size = 0
             field = await multipart.next()
             while field is not None:
-                size = 0
                 field_ct = field.headers.get(hdrs.CONTENT_TYPE)
 
                 if isinstance(field, BodyPartReader):

Source: GitHub Commit Reference

Detection Methods for CVE-2025-69228

Indicators of Compromise

• Unusual memory consumption spikes on servers running AIOHTTP applications
• Multiple HTTP requests with abnormally large numbers of multipart form fields from single sources
• Server process memory growth without corresponding legitimate traffic increases
• Application hangs or crashes due to memory exhaustion

Detection Strategies

• Monitor AIOHTTP server process memory usage and set alerts for abnormal growth patterns
• Implement rate limiting on endpoints that accept multipart form data
• Review application logs for unusual request patterns targeting Request.post() handlers
• Deploy network-level monitoring to detect high-volume multipart requests

Monitoring Recommendations

• Configure memory utilization alerts for Python processes running AIOHTTP applications
• Enable detailed request logging to capture multipart field counts and sizes
• Implement application performance monitoring (APM) to track memory allocation trends
• Set up automated health checks that verify server responsiveness under load

How to Mitigate CVE-2025-69228

Immediate Actions Required

• Upgrade AIOHTTP to version 3.13.3 or later immediately
• Review all application handlers that use the Request.post() method
• Implement additional rate limiting on affected endpoints as a defense-in-depth measure
• Monitor server memory usage until patches are applied

Patch Information

The vulnerability is fixed in AIOHTTP version 3.13.3. The patch modifies the multipart form processing logic to initialize the size counter outside the field iteration loop, ensuring that client_max_size is properly enforced across the entire multipart request. The fix is available in commit b7dbd35375aedbcd712cbae8ad513d56d11cce60. For additional details, refer to the GitHub Security Advisory GHSA-6jhg-hg63-jvvf.

Workarounds

• Implement a reverse proxy with request size limits in front of AIOHTTP applications
• Add application-level middleware to reject requests with excessive multipart fields
• Configure web application firewalls to limit multipart form field counts
• Temporarily disable or restrict access to endpoints using Request.post() if immediate patching is not feasible

# Configuration example - Upgrade AIOHTTP to patched version
pip install aiohttp>=3.13.3

# Verify installed version
pip show aiohttp | grep Version