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posted by NCommander on Monday April 17 2017, @06:20PM   Printer-friendly
from the removing-old-ciphers-is-like-taking-old-yeller-behind-the-barn-... dept.

In the continuing saga of website tinkering and people's love of update posts, I'm back with some backend configuration changes. Right now, things have been relatively quiet on the backend side of things. We've got some good news, and some bad news in this update. That being said, we've made a few small updates over the weekend. Rapid fire style, let's go through them:

CAA Records

CAA records define which certificate authorities (CAs) are allowed to sign your domains. They essentially act as a CA whitelist, and the most recent revisions of the Certificate Authority/Browser Baseline Requirements mandates that CAs check for CAA records and respect them. In line with this policy, we've white-listed Let's Encrypt and Gandi's CAs to issue certificates for SoylentNews for the time being as these are the two CAs currently in use here.

In a fun bit of fail, this is the second time I've tried to deploy CAA, and fortunately managed to succeed this go around. The problem stems from the fact that many versions of BIND except the very latest don't recognize the "CAA" record type, and cause the zone file to not process correctly if it's present. As we're still using an older version of BIND as our master server, I had to manually create TYPE257 records as seen below:

soylentnews.org. 3586 IN TYPE257 \# 16 0005697373756567616E64692E6E6574
soylentnews.org. 3586 IN TYPE257 \# 22 000569737375656C657473656E63727970742E6F7267
soylentnews.org. 3586 IN TYPE257 \# 35 0005696F6465666D61696C746F3A61646D696E40736F796C656E746E 6577732E6F7267
soylentnews.org. 3586 IN TYPE257 \# 12 0009697373756577696C643B

Both htbridge.com and ssllabs.com show that the CAA records are properly encoded, and show an additional green bar that they're in place.

Postfix LogJam

Almost two years ago, the Logjam attack on the DH key exchange was discovered and publicized. As part of our general hardening of SoylentNews, we regenerated all the DH parameters to prevent logjam from being a viable attack vector. Unfortunately, we overlooked the mail STARTTLS services on mail.soylentnews.org, and only caught it when I was checking various security things. The DH parameter files have been regenerated. Under normal circumstances, Logjam can't be exploited unless the underlying SSL cipher is relatively weak. As part of previous hardening, we kicked SSLv3 and many insecure ciphers to the curb, but unfortunately RSA_CBC_IDEA was accidentally left in place as a valid protocol for STARTTLS transport. Based on my understanding of the logjam attack, 1024-bit ciphers like RSA_CBC_IDEA are still difficult to exploit, and its likely only a nation state could successfully have breached it.

Given only SN staff have mail accounts, and that users are encouraged to change their passwords after creating an account, I think its safe to assume that we're relatively OK as far as data security and integrity go since email in general at best is opportunistically encrypted, and should always be assumed to be monitor-able (via a STRIPTLS attack). That being said, if you haven't changed your password from account creation though, it's likely a good idea to do so now.

We discovered our IMAP server has been serving a self-signed certificate during this check as well. We'll be replacing this with a properly signed certificate within the near future. I have other things on this topic that will be noted in a future post, so keep a look out for that.

Disabling HTTP Methods

A routine check of the site's security headers showed that we were accepting HTTP TRACE and other methods we don't need on production. The configuration for nginx has been modified to put a bullet in this behavior. We're still checking to make sure we got this everywhere, but we should be good on at least the production servers for now. This has bumped the site security rating up to an A on the HTBridge; we're still missing the referral security header, but we need to check to make sure there's no user impact before deploying it.

3DES Put Out To Pasture

As always in the world of encryption, various algorithms eventually become insecure and weakened as cryptanalysis gets more and more advanced. A few months ago, the SWEET32 attack against 3DES was discovered which drastically weakens the security of 3DES via the birthday paradox problem. In practice, SWEET32 requires a second exploit to even be usable as SoylentNews only allowed 3DES connections as a last resort if AES wasn't supported. As every major browser has supported AES for years, we decided to put 3DES out to pasture and have removed it from the allowed list of ciphers for SN.

Not too much to note in this round of administration games, but we're working to make overhaul changes to the stack to allow the potential for HPKP key pinning in the near future, as well as deploying TLSA/DANE support for both HTTPS and SMTP on SN. As part of this process, we'll also be enabling HSTS across subdomains, and reissuing our SSL certificates to enable OCSP Must-Staple. We'll keep you guys updated as we move towards that goal!

~ NCommander

 
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  • (Score: 2) by DannyB on Tuesday April 18 2017, @10:03PM (2 children)

    by DannyB (5839) Subscriber Badge on Tuesday April 18 2017, @10:03PM (#496043) Journal

    Without a solid argument why to buy gobs of individual certs instead of one wildcard cert I would get nowhere. I have no doubt I could set up my server for Let's Encrypt. I don't know if that is the case for all other groups that operate servers. The environment I operate in is no doubt different than what you are doing at SN. If there is a solid security argument against wildcard certs, I would be very interested in that.

    --
    Since nobody defrags SSDs anymore, they are more (or less?) prone to failure of their seek mechanisms.
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  • (Score: 2) by NCommander on Tuesday April 18 2017, @10:44PM (1 child)

    by NCommander (2) Subscriber Badge <michael@casadevall.pro> on Tuesday April 18 2017, @10:44PM (#496056) Homepage Journal

    The problem with wildcards is that they represent a considerably high risk factor. For example, imagine that you have www.example.com, mail.example.com, and payment.example.com, and you're in a PCI compliance setup so you've got everything that talks to the outside world living in the DMZ. You buy and deploy a wildcard certificate to all three of these domains to simply deployment and management.

    Now let's say your mail server gets compromised. They now have a valid wildcard certificate that would show the lock for payments.example.com. Depending on your network situation, if the attacker can MitM or change DNS records, he can now decrypt and decode everything going to your payments server even though it was isolated from the mail server because of the wildcard. If we're in a scenario where that the payment and mail server are on the same network segment, an ARP poison attack can easily allow a MITN if you can successfully pwn that mail server. Even beyond that, because most cases when working with wildcards you have the same private key on each box, if any box gets taken down, the attacker can recover the PK, and use it to decrypt SSL traffic in-flight over the network.

    There are technical reasons why SSL wildcards exist, specifically in cases where you can't know all the subdomains in general (i.e., dynamic subdomain generation is a valid case), but those should be few and far between. Wildcards are only really acceptable if they're absolutely necessary.

    This is part what EV certificates disallow wildcard issuance.

    --
    Still always moving
    • (Score: 2) by DannyB on Wednesday April 19 2017, @01:44PM

      by DannyB (5839) Subscriber Badge on Wednesday April 19 2017, @01:44PM (#496289) Journal

      That's a great argument. For anything processing payments, an individual EV certificate would be best.

      --
      Since nobody defrags SSDs anymore, they are more (or less?) prone to failure of their seek mechanisms.