CVE-2025-69227: AIOHTTP DoS Vulnerability Due to Assert Bypass
Summary
CVE-2025-69227: AIOHTTP vulnerable to DoS when bypassing asserts. Affects aiohttp versions < 3.13.3. Fixed in 3.13.3. How to fix ↓
Also tracked for
The same CVE-2025-69227 is tracked separately for each ecosystem and vendor. Its fix information is the same; the package and affected versions differ.
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Background
AIOHTTP is a popular asynchronous HTTP client/server framework for Python, designed to handle HTTP requests and responses efficiently. It is widely used for building web applications and services. The framework provides features such as routing, middleware support, and session management. However, it is susceptible to a denial-of-service (DoS) attack when assert statements are bypassed, particularly when processing POST bodies under specific conditions.
Vulnerability Detail
The vulnerability arises when optimizations are enabled in Python, such as using the '-O' flag or setting 'PYTHONOPTIMIZE=1'. In this state, assert statements in the AIOHTTP framework can be bypassed, leading to an infinite loop during the processing of a POST request. This allows an attacker to craft a malicious message that can cause the application to hang, resulting in a denial-of-service condition. The impact is significant as it can disrupt service availability and affect user experience.
How To Fix
Latest published version: 3.14.5 as of 22 Oct 2026
pip install --upgrade "aiohttp==3.14.5"Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
3.13.3
This is the first release that contains the fix.
pip install --upgrade "aiohttp==3.13.3"Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, avoid using the '-O' optimization flag when running your Python application. This will prevent assert statements from being bypassed, thus mitigating the risk of the vulnerability until you can apply the patch.
Conclusion
The AIOHTTP framework has a vulnerability that can lead to a denial-of-service attack when assert statements are bypassed due to Python optimizations. It is crucial to update to the patched version 3.13.3 or later to mitigate this risk. Additionally, using Vulert can help monitor for such vulnerabilities in real-time.
See every vulnerability recorded for aiohttp →
FAQ
The CVSS score of this vulnerability is 6.6, indicating a medium severity level.
You can use Vulert, which monitors and alerts for open-source vulnerabilities in real-time. You can check your application without any signup using the Vulert playground at Vulert Scanner.
The vulnerability affects all versions of AIOHTTP prior to 3.13.3.
The primary consequence is a denial-of-service attack, which can lead to application downtime and degraded user experience.
Yes, the permanent fix is to update AIOHTTP to version 3.13.3 or later, where the vulnerability has been addressed.
References
Related vulnerabilities
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