SAML roulette: the hacker always wins
Summary: PortSwigger researcher Gareth Heyes documented how chaining round-trip attacks with namespace confusion in the ruby-saml library achieved unauthenticated admin access on GitLab Enterprise, exploiting the fact that REXML parses and validates the signature while Nokogiri reads attributes. The flaws were fixed in GitLab versions 17.9.2, 17.8.5, and 17.7.7 for Community and Enterprise Edition, and GitHub independently found and patched the same vulnerabilities, though its disclosure omitted the specific mutation and unauthenticated exploitation path.
Bottom line: The attack needs no credentials at all: a publicly accessible WS-Federation signed metadata document from the identity provider supplies the valid Signature element, and the only thing an attacker must extract is the application's unique ID, which can be found in the IdP URL or via a search engine.
Read the original at PortSwigger Research ↗
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