CVE-2025-69223: AIOHTTP Zip Bomb DoS Vulnerability

CVE-2025-69223 Overview

CVE-2025-69223 is a Denial of Service vulnerability affecting AIOHTTP, the popular asynchronous HTTP client/server framework for asyncio and Python. Versions 3.13.2 and below are vulnerable to a zip bomb attack that can exhaust the host's memory resources. An attacker can send a specially crafted compressed request that, when decompressed by AIOHTTP, expands to consume excessive memory, leading to server unavailability.

Critical Impact

Remote attackers can cause complete server denial of service by sending malicious compressed requests that exhaust system memory upon decompression.

Affected Products

• AIOHTTP versions 3.13.2 and below
• Python applications using vulnerable AIOHTTP versions for HTTP server functionality
• Asyncio-based web services with compressed request handling enabled

Discovery Timeline

• 2026-01-05 - CVE CVE-2025-69223 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2025-69223

Vulnerability Analysis

This vulnerability is classified under CWE-409 (Improper Handling of Highly Compressed Data). The flaw exists in AIOHTTP's handling of compressed HTTP request bodies. When a server receives a compressed request (using gzip, deflate, or similar encoding), AIOHTTP decompresses the content without proper size limits, allowing a small compressed payload to expand into an extremely large uncompressed data stream.

The attack exploits the asymmetric nature of compression algorithms where a small input can produce disproportionately large output. A zip bomb, sometimes called a "decompression bomb," is a malicious archive designed to crash or render useless the program or system reading it. In this context, an attacker can craft a compressed request body that is only a few kilobytes in size but expands to gigabytes when decompressed, rapidly exhausting available memory.

Root Cause

The root cause is the absence of a maximum decompression size limit in AIOHTTP's payload decompression logic. Prior to the fix, the decompressor would continue expanding data without checking the resulting size, allowing unbounded memory allocation. This oversight means any endpoint accepting compressed request bodies could be targeted.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Crafting a highly compressed payload (zip bomb) with extreme compression ratios
2. Sending an HTTP request with Content-Encoding: gzip (or similar) header
3. Including the malicious compressed payload as the request body
4. The AIOHTTP server automatically decompresses the content, exhausting memory

The attack can be executed remotely against any AIOHTTP server that accepts and decompresses request bodies, making it particularly dangerous for public-facing APIs and web services.

     """Not enough data to satisfy content length header."""
 
 
+class DecompressSizeError(PayloadEncodingError):
+    """Decompressed size exceeds the configured limit."""
+
+
 class LineTooLong(BadHttpMessage):
     def __init__(
         self, line: str, limit: str = "Unknown", actual_size: str = "Unknown"

Source: GitHub Commit

The patch introduces a new DecompressSizeError exception class that is raised when decompressed data exceeds the configured max_length parameter, preventing unbounded memory consumption.

Detection Methods for CVE-2025-69223

Indicators of Compromise

• Abnormally small compressed requests (few KB) arriving at HTTP endpoints
• Sudden memory exhaustion or out-of-memory (OOM) conditions on AIOHTTP servers
• Server crashes or unresponsiveness following receipt of compressed HTTP requests
• Unusual spike in requests with Content-Encoding: gzip or Content-Encoding: deflate headers

Detection Strategies

• Monitor for HTTP requests with compression headers where the compressed size is disproportionately small compared to Content-Length header or decompressed size
• Implement application-level logging to track decompression ratios and flag suspicious patterns
• Deploy memory monitoring alerts to detect sudden memory consumption spikes on AIOHTTP server processes
• Use Web Application Firewall (WAF) rules to limit maximum decompressed payload sizes

Monitoring Recommendations

• Enable memory usage alerts on servers running AIOHTTP applications with thresholds for rapid consumption
• Log all incoming requests with compression encoding headers for forensic analysis
• Monitor process-level memory consumption for AIOHTTP worker processes
• Configure infrastructure monitoring to alert on OOM killer events or process restarts

How to Mitigate CVE-2025-69223

Immediate Actions Required

• Upgrade AIOHTTP to version 3.13.3 or later immediately
• Audit all applications using AIOHTTP for vulnerable version deployments
• Consider temporarily disabling compressed request body handling if upgrade is not immediately possible
• Implement network-level rate limiting for requests with compression encoding headers

Patch Information

The vulnerability is fixed in AIOHTTP version 3.13.3. The fix introduces a max_length parameter to the decompressor that limits the maximum size of decompressed data. When this limit is exceeded, a DecompressSizeError exception is raised, preventing memory exhaustion.

For detailed patch information, see the GitHub Security Advisory and the commit implementing the fix.

Workarounds

• Deploy a reverse proxy (nginx, HAProxy) in front of AIOHTTP servers with decompression limits configured
• Implement request body size limits at the load balancer or WAF level
• If using middleware, add custom decompression handling with explicit size limits before requests reach AIOHTTP
• Consider disabling automatic decompression and handling it manually with size checks

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

# Verify installed version
pip show aiohttp | grep Version