[Openvpn-devel,v2] Always disable TLS renegotiations
Commit Message
Renegotiations have been troublesome in the past and also the recent OpenSSL
security problem (CVE-2021-3449) is only exploitable if TLS renegotiation
is enabled.
mbed TLS disables it by default and says in the documentation:
Warning: It is recommended to always disable renegotation unless you know you
need it and you know what you're doing. In the past, there have been
several issues associated with renegotiation or a poor understanding of
its properties.
TLS renegotiation can be used to restart a session with diffferent
parameters (e.g. now with client certs). This somethign that OpenVPN does
not use.
Furthermore because of all these problems, also TLS 1.3 completely
drops support for renegotiations.
Patch V2: Improve commments and commit message
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
---
src/openvpn/ssl_mbedtls.c | 4 ++++
src/openvpn/ssl_openssl.c | 4 ++++
2 files changed, 8 insertions(+)
Comments
Hi,
On 26/03/2021 17:05, Arne Schwabe wrote:
> Renegotiations have been troublesome in the past and also the recent OpenSSL
> security problem (CVE-2021-3449) is only exploitable if TLS renegotiation
> is enabled.
>
> mbed TLS disables it by default and says in the documentation:
>
> Warning: It is recommended to always disable renegotation unless you know you
> need it and you know what you're doing. In the past, there have been
> several issues associated with renegotiation or a poor understanding of
> its properties.
>
> TLS renegotiation can be used to restart a session with diffferent
too many f
> parameters (e.g. now with client certs). This somethign that OpenVPN does
somethign -> something
> not use.
>
> Furthermore because of all these problems, also TLS 1.3 completely
> drops support for renegotiations.
>
> Patch V2: Improve commments and commit message
too many m :D
>
> Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Antonio Quartulli <antonio@openvpn.net>
Basic connection tests passed, with OpenVPN renegotiations performed
with no issue.
Hi,
On Fri, Mar 26, 2021 at 05:05:45PM +0100, Arne Schwabe wrote:
> + /* Disable TLS renegotiations. OpenVPN's renegotiation creates new SSL
> + * session and does not depend on this feature. And TLS renegotiations have
> + * been problematic in the past */
> + sslopt |= SSL_OP_NO_RENEGOTIATION;
Unfortunately this seems to be not available in OpenSSL 1.0.2, which
is what the OS ships on FreeBSD 11.4 (which is still supported).
../../../openvpn/src/openvpn/ssl_openssl.c:326:15: error: use of undeclared identifier
'SSL_OP_NO_RENEGOTIATION'
sslopt |= SSL_OP_NO_RENEGOTIATION;
gert
@@ -1086,6 +1086,10 @@ key_state_ssl_init(struct key_state_ssl *ks_ssl,
{
mbedtls_ssl_conf_curves(ks_ssl->ssl_config, ssl_ctx->groups);
}
+ /* Disable TLS renegotiations. OpenVPN's renegotiation creates new SSL
+ * session and does not depend on this feature. And TLS renegotiations have
+ * been problematic in the past */
+ mbedtls_ssl_conf_renegotiation(ks_ssl->ssl_config, MBEDTLS_SSL_RENEGOTIATION_DISABLED);
/* Disable record splitting (for now). OpenVPN assumes records are sent
* unfragmented, and changing that will require thorough review and
@@ -320,6 +320,10 @@ tls_ctx_set_options(struct tls_root_ctx *ctx, unsigned int ssl_flags)
sslopt |= SSL_OP_CIPHER_SERVER_PREFERENCE;
#endif
sslopt |= SSL_OP_NO_COMPRESSION;
+ /* Disable TLS renegotiations. OpenVPN's renegotiation creates new SSL
+ * session and does not depend on this feature. And TLS renegotiations have
+ * been problematic in the past */
+ sslopt |= SSL_OP_NO_RENEGOTIATION;
SSL_CTX_set_options(ctx->ctx, sslopt);