Bas Bloemsaat

The `BytesGenerator` class within the email module did not correctly quote newlines for email headers during email message serialization. This flaw allows for header injection when an email is serialized, specifically when using "LiteralHeader" writing headers that do not adhere to email folding rules. The updated behavior rejects incorrectly folded headers in `BytesGenerator`.

The issue concerns the email module in CPython, which did not properly quote newlines for email headers when serializing an email message. This allows for header injection when an email is serialized, potentially enabling a remote authenticated attacker to spoof sender identity, gain unauthorized email sending, or cause loss of control over email communication by persuading a victim to open a specially crafted email.