6.3

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2026-22779

CVE-2026-22779: BlackSheep ClientSession is vulnerable to CRLF injection

BlackSheep is an asynchronous web framework to build event based web applications with Python. Prior to 2.4.6, the HTTP Client implementation in BlackSheep is vulnerable to CRLF injection. Missing headers validation makes it possible for an attacker to modify the HTTP requests (e.g. insert a new header) or even create a new HTTP request. Exploitation requires developers to pass unsanitized user input directly into headers.The server part is not affected because BlackSheep delegates to an underlying ASGI server handling of response headers. This vulnerability is fixed in 2.4.6.

(GitHub Advisory)

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CVE-2026-22779

CVE-2026-22779:

6.3

CVSS Score

4.0

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
blacksheep	pip	< 2.4.6	2.4.6

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability lies in BlackSheep's HTTP client implementation, specifically in the functions responsible for serializing an HTTP request object into raw bytes. The core issue is the lack of input sanitization for carriage return (CR) and line feed (LF) characters in several key functions within the blacksheep.scribe module.

blacksheep.scribe.write_header: This function constructs a single header line. Before the patch, it directly concatenated the header name and value, allowing malicious input containing CRLF sequences to inject new, attacker-controlled headers.
blacksheep.scribe.write_request_method: This function writes the HTTP method to the request line. It lacked validation, permitting an attacker to provide a method string with CRLF characters, which could be used to prematurely end the request line and start injecting other headers or even a second, malicious HTTP request (HTTP Request Splitting).
blacksheep.scribe.write_request_uri: This function constructs the URI part of the request line. It failed to sanitize the URL's path and query components, allowing CRLF characters in these fields to be written directly into the outgoing request, leading to a similar injection vector as with the method.

The patch addresses these vulnerabilities by introducing a _nocrlf utility function that strips \r and \n characters from the input and applying it to header values, URL paths, and queries. Additionally, it enforces strict validation on the HTTP method to ensure it conforms to RFC 7230 token standards, preventing injection through that vector. Any application using BlackSheep's ClientSession to make HTTP requests with user-controllable input for the method, URL, or headers was vulnerable.

Vulnerable functions

blacksheep.scribe.write_header

blacksheep/scribe.py

The function was vulnerable to CRLF injection because it did not sanitize the header name and value before concatenating them into a raw HTTP header string. An attacker could provide a header value containing `\r\n` sequences to inject additional headers into the request.

blacksheep.scribe.write_request_method

blacksheep/scribe.py

The function was vulnerable to CRLF injection because it did not validate the HTTP method string. An attacker could provide a method containing `\r\n` sequences to terminate the request line and inject arbitrary headers or a new request body.

blacksheep.scribe.write_request_uri

blacksheep/scribe.py

The function was vulnerable to CRLF injection because it did not sanitize the URL path or query string. An attacker could provide a URL with `\r\n` sequences in its path or query to inject arbitrary data into the HTTP request line.

Vulnerability Intelligence
Miggo AI

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WAF Protection Rules

WAF Rule

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Reasoning

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