6.3

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2025-69224

CVE-2025-69224: AIOHTTP's Unicode processing of header values could cause parsing discrepancies

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Versions 3.13.2 and below of the Python HTTP parser may allow a request smuggling attack with the presence of non-ASCII characters. If a pure Python version of AIOHTTP is installed (i.e. without the usual C extensions) or AIOHTTP_NO_EXTENSIONS is enabled, then an attacker may be able to execute a request smuggling attack to bypass certain firewalls or proxy protections. This issue is fixed in version 3.13.3.

(GitHub Advisory)

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CVE-2025-69224

CVE-2025-69224:

6.3

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

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability exists in how aiohttp handles HTTP headers containing non-ASCII characters. Specifically, the Upgrade, Content-Encoding, and Transfer-Encoding headers were processed using the .lower() string method before validation. The .lower() method can transform certain unicode characters into different ASCII representations (e.g., the Kelvin sign 'K' becomes 'k').

An attacker could craft a request with a header like Upgrade: websocKet. A front-end proxy might not perform the same unicode normalization and see a header it doesn't understand, passing it to the backend. The vulnerable aiohttp application, however, would convert websocKet to websocket and might upgrade the connection. This discrepancy in parsing between the proxy and the backend application is what enables an HTTP Request Smuggling attack.

The patch addresses this by adding an .isascii() check on the header values before calling .lower(). This ensures that any non-ASCII characters, which are not compliant with the relevant RFCs for these headers, cause the header to be rejected or ignored, preventing the parsing discrepancy.

The vulnerable functions are those responsible for parsing these specific headers in the pure Python implementation (aiohttp/http_parser.py), which is used when C extensions are not available. The same fix was applied to the Cython implementation (aiohttp/_http_parser.pyx) for consistency and to prevent the vulnerability in case it's used. The key vulnerable functions are _is_supported_upgrade, HttpParser.parse_headers, and HttpParser._is_chunked_te in the Python module, and HttpParser.on_headers_complete in the Cython module.

Vulnerable functions

_is_supported_upgrade

aiohttp/http_parser.py

The function processes the 'Upgrade' header. It uses `.lower()` on the header value without ensuring it is ASCII. Certain unicode characters can be transformed by `.lower()` in a way that could bypass security checks, leading to request smuggling if a proxy interprets the header differently.

HttpParser.parse_headers

aiohttp/http_parser.py

The function processes the 'Content-Encoding' header. It uses `.lower()` on the header value before checking for supported compression types. A malicious non-ASCII header value could be misinterpreted after being converted to lowercase, potentially leading to request smuggling.

HttpParser._is_chunked_te

aiohttp/http_parser.py

This function checks for the 'chunked' value in the 'Transfer-Encoding' header. It uses `.lower()` on a part of the header value. A crafted non-ASCII value could be transformed by `.lower()` to 'chunked', causing a discrepancy in how the message is parsed between aiohttp and an upstream proxy, which is the basis for a request smuggling attack.

HttpParser.on_headers_complete

aiohttp/_http_parser.pyx

This Cython function is the equivalent of the Python header parsing logic. It has the same vulnerabilities related to calling `.lower()` on 'Upgrade' and 'Content-Encoding' header values without validating they are ASCII. This could lead to request smuggling.

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Miggo AI

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WAF Rule

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Reasoning

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