The vulnerability arises from a lack of validation in BlackSheep’s HTTP Client, allowing malicious input to inject Carriage Return and Line Feed characters into request headers. This injection can alter the outgoing request or create a new HTTP request entirely by appending arbitrary headers. Because the server component delegates response handling to the underlying ASGI server, only the client side is affected. The flaw provides a route for altering request semantics without the protecting infrastructure, potentially leading to information disclosure or request forging if the crafted headers influence downstream services.

Neoteroi’s BlackSheep asynchronous web framework, versions prior to 2.4.6, is impacted. Any Python application building its own HTTP client using these versions may propagate unsanitized header values into outgoing requests.

The CVSS score of 6.3 indicates a moderate severity, while an EPSS of less than 1% reflects a very low intent or probability of exploitation in the wild. The flaw is not listed in the CISA KEV catalog, suggesting no known widespread exploitation. Exploitation requires developers to inject unsanitized user data into header fields. If an attacker can influence that input, they can modify request headers to influence the behavior of downstream services or insert harmful headers, but the likelihood of such injection in production environments is low and the impact is contained to the client-side request path.