tl;dr I found a severe issue in the Slack's SAML implementation that allowed me to bypass the authentication. This has now been solved by Slack.
IMHO the rule #1 of any bug hunter (note I do not consider myself one of them since I do this really sporadically) is to have a good RSS feed list. In the course of the last years I built a pretty decent one and I try to follow other security experts trying to "steal" some useful tricks. There are many experts in different fields of the security panorama and too many to quote them here (maybe another post). But one of the leading expert (that I follow) on SAML is by far Ioannis Kakavas. Indeed he was able in the last years to find serious vulnerability in the SAML implementation of Microsoft and Github. Usually I am more an "OAuth guy" but since both, SAML and OAuth, are nothing else that grandchildren of Kerberos learning SAML has been in my todo list for long time. The Github incident gave me the final…
Yesterday while reading my Twitter stream I found this interesting article about downloading GitHub SSO bypass codes. Same as Yasin Soliman I was invited to a Github pre-release of the organisation SAML single sign-on (SSO) private program. And same as him I found an issue in the same endpoint. So I thought to write a quick blog post about it.
Github already published a tl;dr about this,
I will try to fill the blanks here.
As mentioned by Yasin, Github offers an endpoint where privileged users can recover bypass codes. These recovery codes were accessible for download as plaintext and had the content-type as text/plain, something like: