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Comment by beny23 | Hacker News Reader

I wouldn't have thought this an issue if you're behind an AWS WAF or LB? (and assuming AWS is patched already)

This vulnerability affects parsing maliciously crafted certificates, so it will mostly affect clients. If your app is fetching data from a 3rd party and validating its certificate, it may be vulnerable, regardless of how you are fronting requests to your site.

> This vulnerability affects parsing maliciously crafted certificates, so it will mostly affect clients.

Actually, it is the opposite.

You seem to be unaware of the fact that servers do receive certificates from the clients which are then parsed.

Which is already mentioned in the advisory document:

  "Thus vulnerable situations include:

   - TLS clients consuming server certificates
   - TLS servers consuming client certificates <---- here
   - Hosting providers taking certificates or private keys from customers
   - Certificate authorities parsing certification requests from subscribers
   - Anything else which parses ASN.1 elliptic curve parameters"

That's not how the TLS handshake works. The TLS server must be configured to request a certificate from the client in order for the client to know that it needs to send a client certificate to the server, and that server-side configuration is disabled for ~99%+ of endpoints.

TLS server implementations should be aborting the TLS connection for violating the TLS Handshake state machine if a client attempts to send a client certificate when it wasn't requested.

So while this bug affects both clients and servers, 100% of clients are parsing the server's TLS cert during the TLS handshake, but less than ~1% of servers are parsing a client's certificate during a handshake.

There is very little reason to DOS a client and a lot of reasons to attack servers.

There is a huge number of public facing services that implement mutual auth and all those are potentially vulnerable to DOS. While clients can just decide to not connect to a web service that causes their browser to malfunction (and why have you connected there in the first place?), services are usually not at liberty to ignore a client at this stage.

So yes, those servers that do request client certificate are targets and my point still stands that servers are much more affected than the clients.

What would be an affected client? You keep connecting to this infected website that causes your browser to die? Somebody embedded some tracking on their page that now points to an infected website? Everybody will just move on and it is hard to say you are very much affected by this problem.

Whereas if you are a service and you are affected you absolutely need to implement a fix.

correction: literally 99.99999% of endpoints. they use password^W SMS authentication instead. no seriously, how is the only one good thing about X.509 (authentication via public key) the only unused part (to be fair, if anyone used it, wed have a whole new 10 episodes of vuln disclosures).

> correction: literally 99.99999% of endpoints.

You made up a number with no grounding in reality because of your bias due to being "general public".

For corporate services it is actually quite common to use client certificates and mutual auth. Also popular with VPNs.

You might not be aware of this because corporations do not want to deal with people who do not know or can be forced to know how to generate signing request.

This is different when you control both the service and the users of the service and you have something valuable to protect.

As an example, I worked with credit card terminals and these used mutual auth with properly managed client certificates.

You wouldn't call DOS on all terminals and ATMS "insignificant".

No, I was purely focused on public web. As for your corporate services, those are all insecure as hell despite whaever tech they use. Anything that's remotely hidden from public in any way historically was uncovered to have non stop, gaping, and obvious security holes, even after being corrected 1-5 times. This is a result of the way businesses are run as miniature reactionary states ("just ban people in the firewall brother. call the police").

For an intermediary like a WAF, load-balancer, or CDN to help it needs to do all of the certificate processing and keep your backend app from seeing the certificate at all. If you are terminating HTTPS at the edge and using HTTP internally that's very likely but if you're using an NLB instead of an ALB, it's not. Similarly, you'd also want to see if there's any application-level path where a certificate would be included in an uploaded file but that's far less common.

Depends if s2n is vulnerable to the same bug. Of course AWS doesn't protect you against application bugs so if your application has an SSRF vulnerability (presumably otherwise unexploitable) an attacker might be able to DoS you.

They don't mention S/MIME or things like signed binaries or SAML assertions but those seem plausibly vulnerable as well.

I think nearly everything at AWS uses s2n and not OpenSSL these days

Has s2n been fips certified? I thought some things (govcloud?) were still using openssl due to fips requirements.

I'm not sure what they are using right now, but they currently have the "AWS-LC Cryptographic Module" listed as being in process for validation which may be sufficient for s2n.

I know there are other AWS features/services that are lined up behind that validation for FIPS support.

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