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Impact
The package does not validate the ACS Location URI according to the SAML binding being parsed.
If abused, this flaw allows attackers to register malicious Service Providers at the IdP and inject Javascript in the ACS endpoint definition, achieving Cross-Site-Scripting (XSS) in the IdP context during the redirection at the end of a SAML SSO Flow.
Consequently, an attacker may perform any authenticated action as the victim once the victim’s browser loaded the SAML IdP initiated SSO link for the malicious service provider.
Note: The severity is considered “High” because the SP registration is commonly an unrestricted operation in IdPs, hence not requiring particular permissions or publicly accessible to ease the IdP interoperability.
Patches
This issue is fixed in 0.4.14
Workarounds
Users of the package can perform external validation of URLs provided in SAML metadata, or restrict the ability for end-users to upload arbitrary metadata.
References
This issue was reported by Francesco Lacerenza from Doyensec.
The crewjam/saml go library contains a partial implementation of the SAML standard in golang. Prior to version 0.4.13, the package's use of flate.NewReader does not limit the size of the input. The user can pass more than 1 MB of data in the HTTP request to the processing functions, which will be decompressed server-side using the Deflate algorithm. Therefore, after repeating the same request multiple times, it is possible to achieve a reliable crash since the operating system kills the process. This issue is patched in version 0.4.13.
An authentication bypass flaw was discovered in the crewjam/saml go package. A remote unauthenticated attacker could trigger it by sending a SAML request. This would allow an escalation of privileges and then enable compromising system integrity.
A signature verification vulnerability exists in crewjam/saml. This flaw allows an attacker to bypass SAML Authentication. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.