How do I fix 'the SSL server certificate authority is not trusted' message in browser?

-1

It started a few weeks ago. One of sites gives me a message

NET::ERR_CERT_WEAK_SIGNATURE_ALGORITHM

You attempted to reach some_web_site.org, but the server presented a certificate signed using a weak signature algorithm (such as SHA-1). This means that the security credentials the server presented could have been forged, and the server may not be the server you expected (you may be communicating with an attacker).

And when I click proceed I get:

Reason : The SSL server certificate authority is not trusted.

It's one of the state public service sites.

From my firewall I downloaded SSL proxy default authority certificate as p12 file and installed it in Windows in my trusted root CA. This certificate is valid until May 2022.

However, nothing changes. Is it my fault or the server owner?

Update: The site loads just fine outside of my organisation's LAN. I can load it via my mobile phone 4G network. My firewall does web filtering and SSL inspection. Does it mean that my proxy certificate is invalid? Why did it work a few weeks before and I didn't change anything from my side?

Update2 Screenshots added

Hrvoje T

Posted 2018-11-14T10:28:27.520

Reputation: 1 809

Its a problem the server owner must fix. They may not even be aware of the problem though. Especially government services sites usually have to hear it from their clients first that there is a problem before they attempt to fix it, then after they hear it, it will take some time before things get fixed. – LPChip – 2018-11-14T10:54:40.433

One way to be absolutely sure its not on your end: try with different browsers and try with different devices (pc, laptop, smartphone, etc) – LPChip – 2018-11-14T10:56:15.813

From my LAN, over my firewall it doesn't work with different devices. It works from outside of my LAN, if I go with my phone with my mobile internet provider connection. – Hrvoje T – 2018-11-14T11:01:54.770

What if you use your phone using your Wifi? Does it then work? Mobile browsers are different than pc browsers and possibly are less secure. In order to make sure you experience the same, test using the Chrome app on your phone and Chome desktop version on your pc. I estimate that both will fail the site regardless on what network you are. – LPChip – 2018-11-14T11:28:17.377

Using my WiFi over phone also fails to load a site. It's Android 8 with lastest Chrome. – Hrvoje T – 2018-11-14T11:31:35.337

So... if your phone using WiFi does not load the site in Chrome, but going to mobile carrier does work on Chrome, then the problem is on your end. Please edit your post to include this information, its crucial, because it invalidates the answer. – LPChip – 2018-11-14T11:43:25.700

Ok, but I said I have the firewall with proxy certificate. – Hrvoje T – 2018-11-14T11:50:45.487

Answers

You seem to be correct in your suspicions: according to the error message, your proxy certificate uses a SHA-1 signature algorithm, which has a serious known weakness. The validity time is not the issue; the bad algorithm is.

The process to deprecate the SHA-1 algorithm started years ago: with Chrome it started in 2014, as it started to flag end-entity certificates that were using SHA-1 and were valid past January 1, 2017 as "secure, but with minor errors". As time passed and new ways to exploit the weakness were discovered, the flagging was extended in steps to all SHA-1 non-root certificates and made more strict: by now, any up-to-date web browser will mark a site with a SHA-1 certificate anywhere in its certificate chain as unequivocally bad.

Certification authorities compliant with CAB/F baseline requirements stopped issuing any new SHA-1 certificates at the start of year 2016.

Microsoft also went through the process to deprecate SHA-1 certificates in 2017.

If your firewall/proxy still uses a certificate with a SHA-1 signing algorithm, it looks like you've been sort of asleep at the wheel for a while. It became apparent only now probably because of some recent security patch that finally made the SHA-1 algorithm as categorically distrusted everywhere.

You should make sure your proxy can use certificates with better algorithms (if it is up to date and can handle modern TLS on websites, it probably already can), and create a new SSL proxy default authority certificate that uses SHA256 instead of SHA-1. You'll need to distribute it to all the clients whose SSL/TLS traffic you wish to monitor. Once distributed, you can switch your proxy to use the new certificate.

With the screenshots added, it look like the browser actually is mostly happy with the certificate it is getting, as there is a good padlock icon in the address bar. The actual error message is shown instead of the page content, which makes me think this is the proxy's way of telling about a certificate validation failure on the connection between the proxy and the target site.

In the first screenshot, you're browsing outside the LAN and the actual certificate of the site can be seen. Note that it's been renewed recently, as its validity time started on 15.10.2018. The CA certificate used to certify the site is "Thawte RSA CA 2018", so even the CA certificate is at most one year old.

You might actually have a combination of two problems:

the browser was unhappy about the proxy's certificate with the deprecated SHA-1 algorithm, but for the time being, it still considers that a forgivable thing.
and the proxy was unhappy because it does not have either the "Thawte RSA CA 2018" intermediate certificate or its parent, the "DigiCert Global Root CA" certificate in its own store of trusted CA certificates, and so it cannot verify the site's recently-updated actual certificate.

At the time of this writing, the relevant Thawte CA & intermediate certificates seem to be available here.

telcoM

Posted 2018-11-14T10:28:27.520

Reputation: 2 016

Can I create it or I have to buy it or should I call Stormshield to get one? – Hrvoje T – 2018-11-14T15:24:21.573

And how is some sites with https working fine and some not? My ssl filter should inspect all ssl traffic? – Hrvoje T – 2018-11-14T15:31:36.647

If you're uncertain, you should probably consult the documentation of your proxy. But since a SSL proxy certificate allows what is effectively a man-in-the-middle attack on SSL/TLS encrypted traffic, it would make sense for you to handle your own certificate. That way only you (and not the firewall company too) will have the ability to monitor traffic on your client systems. – telcoM – 2018-11-14T15:32:57.203

There are newer techniques like HPKP, CT and DANE which can be used to give the browser more information about the certificate expected on a particular site. Your proxy might not be able to circumvent all these methods. That would cause the sites that have started to use one of these methods to fail while other sites that aren't using those techniques yet will still work.

– telcoM – 2018-11-14T15:45:25.287

If the problem turns out to be caused by HPKP or CT combined to a browser feature that "remembers" the certificates previously seen on HTTPS sites, you might have problems with users that need to use their browsers both inside and outside the company network. (I misremembered: DANE is more of an email thing.) – telcoM – 2018-11-14T15:54:10.493

I added some screenshots – Hrvoje T – 2018-11-15T11:41:38.143

Thanks for your help! Now I need only to find a way how to solve those issues. – Hrvoje T – 2018-11-15T19:09:28.393

Looks like you can find Thawte's latest intermediate & root certificates here. If you add them to your proxy's store of trusted CA certificates (check the admin documentation of your proxy), that should allow connections at least with the browser's click-through "weak signature algorithm" warning. Getting rid of the browser's warning may require tweaking the proxy's client-side SSL/TLS configuration and/or regenerating its CA certificate using a stronger algorithm. Proxy's tech support (Stormshield?) can probably help.

– telcoM – 2018-11-19T10:34:51.067

The problem cannot be fixed, except by the owner of the site getting a proper SSL certificate.

It can be worked around, for example in Chrome by adding to the shortcut the parameter of --ignore-certificate-errors.

However, with the current clamp-down on security, such workarounds have a short life-time.

harrymc

Posted 2018-11-14T10:28:27.520

Reputation: 306 093

I started Chrome with chrome --ignore-certificate-errors, but the site is still blocked. – Hrvoje T – 2018-11-14T11:12:41.940

Sorry, Chrome is changing the rules continuously and apparently doesn't accept overriding this particular error. Try maybe this answer for Firefox.

– harrymc – 2018-11-14T11:16:05.897

Can't load this certificate in Authorities firefox certificates because it's personal certificate firefoy says. Then I tried to import it in 'people' certs and nothing happens. Still fails to load a site – Hrvoje T – 2018-11-14T11:34:32.997

If the comment exchange is correct, it is a problem on the internet connection because if I understood OP correctly, it does not happen on Chrome on the phone if they turn off WiFi and use their mobile connection instead. – LPChip – 2018-11-14T11:44:09.600

@LPChip: The difference might be in the browser on the phone. He also says it works outside of his organization's LAN, so it might also be the corporate firewall that refuses it. Hrvoje: If we had a screenshot of the browser page with the error we might know more. – harrymc – 2018-11-14T13:36:21.600

I added screenshots – Hrvoje T – 2018-11-15T11:41:20.150

I still think that if you are getting different results inside and outside the organization's LAN, you should discuss this with the LAN administrator. A screenshot of the error page inside the LAN might be useful. – harrymc – 2018-11-15T11:51:13.980

Lol, I am the LAN admin. How would I than have access to the firewall :) – Hrvoje T – 2018-11-15T16:42:50.607

I would like an screenshot of the error page in the browser. As admin, you should also be able to give details about your firewall and architecture in general. – harrymc – 2018-11-15T16:44:59.350

This site would not exist if everybody knows everything. Im not afraid to ask. As for the browser error, I already wrote it in the OP NET::ERR_CERT_WEAK_SIGNATURE_ALGORITHM. However, I can take that sceenshot tomorow. Thanks for your help. – Hrvoje T – 2018-11-15T19:05:59.803