Ignore Certificate Errors

[Maxim Dounin]

Hello!

On Thu, Aug 30, 2018 at 09:09:44AM -0700, Roger Fischer wrote:

> Hello,
> 
> is there a way to make NGINX more forgiving on TLS certificate errors? Or would that have to be done in OpenSSL instead?
> 
> When I use openssl s_client, I get the following errors from the upstream server:
> 
> 140226185430680:error:0407006A:rsa routines:RSA_padding_check_PKCS1_type_1:block type is not 01:rsa_pk1.c:103:
> 140226185430680:error:04067072:rsa routines:RSA_EAY_PUBLIC_DECRYPT:padding check failed:rsa_eay.c:705:
> 140226185430680:error:1408D07B:SSL routines:ssl3_get_key_exchange:bad signature:s3_clnt.c:2010:
> 
> This causes NGINX (reverse proxy) to return 502 Bad Gateway to the browser.
> 
> The NGINX error log shows:
> 
> 2018/08/29 09:09:59 [crit] 11633#11633: *28 SSL_do_handshake() failed (SSL: error:0407006A:rsa routines:RSA_padding_check_PKCS1_type_1:block type is not 01 error:04067072:rsa routines:RSA_EAY_PUBLIC_DECRYPT:padding check failed error:1408D07B:SSL routines:ssl3_get_key_exchange:bad signature) while SSL handshaking to upstream, client: 192.168.1.66, server: s5.example.com, request: "GET /xyz
> 
> I have added “proxy_ssl_verify off;”, but that did not make any difference.
> 
> Surprisingly, the browser (directly to the upstream server) does not complain about the TLS error.
> 
> Is there anything else I can do either in NGINX or openssl to suppress the 502 Bad Gateway?
> 
> Thanks…
> 
> Roger
> 
> PS: I don’t have control over the upstream server, so I can’t fix the root cause (faulty certificate).

As per the error message, the problem seems to be not with the 
cerifitcate, but with the key exchange during the SSL handshake.  
For some reason signature verification after the key exchange 
fails due to wrong padding.

Most likely the problem is specific to some ciphers, so forcing a 
different cipher with proxy_ssl_ciphers could help, see 
http://nginx.org/r/proxy_ssl_ciphers.

-- 
Maxim Dounin
http://mdounin.ru/