ssl.create_default_context() sets OP_NO_COMPRESSION to prevent CRIME

Lib/ssl.py

@@ -383,6 +383,8 @@ def create_default_context(purpose=Purpose.SERVER_AUTH, *, cafile=None,
     context = SSLContext(PROTOCOL_TLSv1)
     # SSLv2 considered harmful.
     context.options |= OP_NO_SSLv2
+    # disable compression to prevent CRIME attacks (OpenSSL 1.0+)
+    context.options |= getattr(_ssl, "OP_NO_COMPRESSION", 0)
     # disallow ciphers with known vulnerabilities
     context.set_ciphers(_RESTRICTED_CIPHERS)
     # verify certs in client mode

Misc/NEWS

@@ -18,6 +18,8 @@ Core and Builtins
 Library
 -------
 
+- ssl.create_default_context() sets OP_NO_COMPRESSION to prevent CRIME.
+
 - Issue #19802: Add socket.SO_PRIORITY.
 
 - Issue #11508: Fixed uuid.getnode() and uuid.uuid1() on environment with