SAML Is a Fractal of Bad Design—It's Time to Deprecate It
SAML: A Fractal of Bad Design
SAML, born from a committee that merged four XML security protocols, is crushed by its own complexity. XML signature wrapping attacks from 2012 still work today. Canonicalization, enveloped signatures, kitchen-sink design, and ossification make it a fractal of bad design. I worked on Duo's first SAML gateway and saw the flaws firsthand. Modern alternatives like OpenID Connect are the way forward.
What's insidious about SAML is that it really is mostly straightforward to understand, but it's built on a foundation of sand, bone dust, and ash; it works … if you assume XML signature validation is reliable. But XML signature validation is deeply cursed, and is so complicated that most fielded SAML implementations are wrapping libxmlsec, a gnarly C codebase nobody reads.
- bawolff
My favourite SAML horror story, is that it used to be, that by default the main c implementation of xmlsig would not just check the sig with the public key specified but would also:
- check it against an hmac using a password specified in the attacker controlled document.
- check the signature using web pki (so the attacker could sign the saml document with their TLS key for their own personal domain and it would always be considered valid)
I honestly dont know how sites with saml arent getting hacked all the time. The only thing worse than the absolute terrible standards are the absolute terrible implementations.
- jmbwell
It’s such a product of “Ooh! Markup languages! What can we use a markup language to solve!” When authentication is just not a document or data stream that needs marked-up.
The article rightly connects this to XML, which was indeed the hammer to everything’s nail at the time
I think we aren’t done with this problem yet, though. OIDC makes a lot of assumptions in service to Google and others. And tailscale as mentioned, despite “holding the line,” already reveals the cracks when things like GitHub accounts have to be treated differently from others.
What we are missing is a provider-independent way to do this. I should be able to create an account and log in just about anywhere using a backend I control. It can be done, but not with what we have today
- cameronh90
SAML sucks, but it still has a bunch of features for its specific narrow enterprise SSO use-case that OIDC lacks - most notably IdP-initiated flow. OIDC is a constellation of specs with inconsistent support across products, whereas the commonly-implemented subset of SAML is more-or-less stable in its mediocrity.
OIDC will eventually displace SAML, but if you're selling to enterprises you should really support both. Both will pale compared to the amount of time you spend dealing with SCIM inconsistencies between IdPs anyway.
- tehnoslow
A fair criticism of the article is that it lists SAML's vulnerabilities but doesn't do the same comparison for OIDC. OIDC has its own problems too: JWT algorithm confusion, none algorithm attacks, missing audience checks, and bugs in JOSE libraries
- arpinum
SAML is even worse than the article describes, problems like needing to check what the signature actually signs. But I'm optimistic about the future, instead of relying on libraries that do a lot, such as general xml parsing, we can support a subset of SAML and only the dialects of the top ~10 providers. Extreme niche providers can be added ad-hoc and only if the deal size makes it worthwhile.
- fire7000
“ Further, a committee of subcommittees having meetings is a recipe for “kitchen-sink” protocol design (e.g., waterfall methodology, big design up front, etc.).”
- personally, I like having a kitchen sink
- pocksuppet
It's called design by committee. It's when you get everyone in a room and nobody can make a tradeoff because it would hurt someone else's pet use case, so you don't actually design anything at all, just build a framework within which a design can exist.
Anyone who has used Wireguard and OpenVPN will spot the difference. OpenVPN is the design-by-committee, Wireguard is the focused opinionated design by someone with a vision. OpenVPN does more things, but if your use case is one that suits Wireguard, Wireguard does it much better.
You also see it with OSI stack versus IP. OSI invented all these layers for proving identity, establishing circuits, sessions, different billing models, collect calls, quality of service, all that stuff. IP looked at that and said: fuck that noise - we send packets, if they don't arrive we send them again, job done. Nobody uses the OSI stack, even though IP fits the OSI model loosely enough that they still teach it, and X.509 got reused as boilerplate for WebPKI certificates.
XML vs JSON is another one. Granted marked-up text, which XML was actually designed for, is very ugly in JSON, but even in that use case, XML has way too much complexity.
If the IP, Wireguard or JSON people designed an SSO system you'd telnet or HTTP into the authenticating party, perform its login steps, get a token you could copy-paste into the relying party and it would check back with the authenticating party to see if the token is valid and the username of the person who sig […]
- sandeepkd
May be I am in a minority here, but there are areas where SAML sort of shines
1. For OIDC/OAuth2 the request has to originate from Service provider, most Enterprise IDP's rely on SAML for Single Sign on cause of its ability to do IDP initiated flows
2. The security for SAML is baked into the payload itself, provides safety against MITM attacks, even though the HTTPS provides similar guarantees in theory, the reality is that your SSL offloading happens elsewhere, not on your application server
The OP provided a list of vulnerabilities discovered in SAML, IMO this kind of comparison if flawed if you do not present the same for OIDC/OAuth2.
At the end of the day, these are tools and effectiveness of a tool is a lot dependent on ones skillset to understand and use the tool.