Disallow SSL renegotiation

michaelpq · michaelpq · commit 01e6f1a842f4 · 2021-05-25T10:10:09.000+09:00
SSL renegotiation is already disabled as of 48d23c7, however this does not prevent the server to comply with a client willing to use renegotiation. In the last couple of years, renegotiation had its set of security issues and flaws (like the recent CVE-2021-3449), and it could be possible to crash the backend with a client attempting renegotiation. This commit takes one extra step by disabling renegotiation in the backend in the same way as SSL compression (f9264d1) or tickets (97d3a0b). OpenSSL 1.1.0h has added an option named SSL_OP_NO_RENEGOTIATION able to achieve that. In older versions there is an option called SSL3_FLAGS_NO_RENEGOTIATE_CIPHERS that was undocumented, and could be set within the SSL object created when the TLS connection opens, but I have decided not to use it, as it feels trickier to rely on, and it is not official. Note that this option is not usable in OpenSSL < 1.1.0h as the internal contents of the *SSL object are hidden to applications. SSL renegotiation concerns protocols up to TLSv1.2. Per original report from Robert Haas, with a patch based on a suggestion by Andres Freund. Author: Michael Paquier Reviewed-by: Daniel Gustafsson Discussion: https://postgr.es/m/YKZBXx7RhU74FlTE@paquier.xyz Backpatch-through: 9.6
diff --git a/src/backend/libpq/be-secure-openssl.c b/src/backend/libpq/be-secure-openssl.c
@@ -251,6 +251,16 @@ be_tls_init(bool isServerStart)
 	/* disallow SSL compression */
 	SSL_CTX_set_options(context, SSL_OP_NO_COMPRESSION);
 
+#ifdef SSL_OP_NO_RENEGOTIATION
+
+	/*
+	 * Disallow SSL renegotiation, option available since 1.1.0h.  This
+	 * concerns only TLSv1.2 and older protocol versions, as TLSv1.3 has no
+	 * support for renegotiation.
+	 */
+	SSL_CTX_set_options(context, SSL_OP_NO_RENEGOTIATION);
+#endif
+
 	/* set up ephemeral DH and ECDH keys */
 	if (!initialize_dh(context, isServerStart))
 		goto error;
