Compliance Impact

This vulnerability allows attacker-controlled input to be injected into multipart/payload headers, potentially modifying requests by injecting additional headers or altering request contents.

If an application passes user-controlled strings into multipart headers without proper sanitization, it could lead to unauthorized manipulation of HTTP requests.

Such unauthorized request modifications could impact the confidentiality and integrity of data transmitted by the application, which are key concerns in compliance with standards like GDPR and HIPAA.

Therefore, failure to mitigate this vulnerability might increase the risk of non-compliance with these regulations due to potential data manipulation or leakage.

Mitigation involves upgrading to aiohttp version 3.14.0 or later and sanitizing user input to prevent header injection.

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Executive Summary

CVE-2026-50269 is a low-severity vulnerability in the aiohttp library (versions prior to 3.14.0) that allows an attacker to inject additional HTTP headers or modify request contents by exploiting improper handling of attacker-controlled input in multipart or payload headers.

Specifically, if an application passes user-controlled strings into MultipartWriter.append(headers=...) or Payload.headers, an attacker can insert carriage return and line feed characters (CRLF) to manipulate the request headers.

This vulnerability is categorized under CWE-93 and CWE-113, which relate to improper neutralization of CRLF sequences in HTTP headers.

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Impact Analysis

If your application uses aiohttp versions prior to 3.14.0 and passes user-controlled input into multipart or payload headers, an attacker could exploit this vulnerability to inject additional headers or alter the contents of HTTP requests.

This could lead to unexpected behavior such as header injection attacks, which might be used to bypass security controls, manipulate request routing, or cause other unintended effects depending on how the headers are processed downstream.

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Detection Guidance

This vulnerability involves attacker-controlled input being included in multipart/payload headers to inject additional headers or modify requests. Detection involves identifying if your application passes user-controlled strings into MultipartWriter.append(headers=...) or Payload.headers.

To detect potential exploitation, you can monitor HTTP requests for unusual or unexpected headers, especially those containing carriage return (\r), line feed (\n), or null byte (\x00) characters which are indicators of header injection attempts.

While no specific commands are provided in the resources, general network monitoring tools like tcpdump or Wireshark can be used to capture HTTP traffic and inspect multipart headers for suspicious characters or injected headers.

• Use tcpdump to capture HTTP traffic: tcpdump -i <interface> -A 'tcp port 80 or 443'
• Use Wireshark to filter and analyze HTTP multipart requests for unusual header content.
• Review application logs for any unexpected header values or errors related to multipart header processing.

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Mitigation Strategies

The primary mitigation is to upgrade the aiohttp library to version 3.14.0 or later, where this vulnerability is fixed.

If upgrading immediately is not possible, sanitize all user-controlled input that is passed into MultipartWriter.append(headers=...) or Payload.headers to ensure it does not contain carriage return, line feed, or null byte characters.

Implement input validation to reject or escape potentially dangerous characters that could be used for header injection.

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