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PYSEC-2026-1222
blacksheepImpact
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.
Attack vector: Applications using user input in HTTP client requests (method, URL, headers).
Patches
Users who use the HTTP Client in BlackSheep should upgrade to 2.4.6.
Workarounds
If users handle headers from untrusted parties, they might reject values for header names and values that contain carriage returns.
References
https://owasp.org/www-community/vulnerabilities/CRLF_Injection
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.
Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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