6.6

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2025-69227

CVE-2025-69227: AIOHTTP vulnerable to DoS when bypassing asserts

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Versions 3.13.2 and below allow for an infinite loop to occur when assert statements are bypassed, resulting in a DoS attack when processing a POST body. If optimizations are enabled (-O or PYTHONOPTIMIZE=1), and the application includes a handler that uses the Request.post() method, then an attacker may be able to execute a DoS attack with a specially crafted message. This issue is fixed in version 3.13.3.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2025-69227

CVE-2025-69227:

6.6

CVSS Score

4.0

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
aiohttp	pip	<= 3.13.2	3.13.3

Technical Details

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Root Cause Analysis

The vulnerability is a Denial of Service (DoS) caused by an infinite loop when processing multipart POST requests in aiohttp. The root cause is the use of assert statements for critical validation within the multipart parsing logic. When a Python application is run in an optimized mode (with the -O flag or PYTHONOPTIMIZE=1), these assert statements are compiled out and ignored.

An attacker can exploit this by sending a specially crafted multipart POST request that violates the assumptions enforced by the asserts. Specifically:

In aiohttp.web_request.Request.post, an assert checked that each multipart field had a name. Without this check, the loop processing fields could misbehave.
In aiohttp.multipart.BodyPartReader.read_chunk, an assert validated the CRLF at the end of a part. Bypassing this allows the parser to enter an invalid state.
In aiohttp.multipart.BodyPartReader._read_chunk_from_stream, an assert prevented reading past the end of the stream, which could also lead to an infinite loop.

The combination of these bypassed checks allows the while loop in Request.post to continue indefinitely, consuming CPU and rendering the service unresponsive. The patch rectifies this by replacing the assert statements with explicit ValueError exceptions, which are not removed during optimization, thus ensuring the validation logic is always executed.

Vulnerable functions

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WAF Rule

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Reasoning

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