> SAML (Security Assertion Markup Language) is an open standard for exchanging authentication and authorization data between parties, in particular, between an identity provider and a service provider. While SAML is widely used to facilitate single sign-on (SSO) and other federated authentication scenarios, improper implementation or misconfiguration can expose systems to various vulnerabilities.
Signatures which are not signed by a real CA are prone to cloning. Ensure the signature is signed by a real CA. If the certificate is self-signed, you may be able to clone the certificate or create your own self-signed certificate to replace it.
> [...]accepting unsigned SAML assertions is accepting a username without checking the password - @ilektrojohn
The goal is to forge a well formed SAML Assertion without signing it. For some default configurations if the signature section is omitted from a SAML response, then no signature verification is performed.
Example of SAML assertion where `NameID=admin` without signature.
XML Signature Wrapping (XSW) attack, some implementations check for a valid signature and match it to a valid assertion, but do not check for multiple assertions, multiple signatures, or behave differently depending on the order of assertions.
- **XSW1**: Applies to SAML Response messages. Add a cloned unsigned copy of the Response after the existing signature.
- **XSW2**: Applies to SAML Response messages. Add a cloned unsigned copy of the Response before the existing signature.
- **XSW3**: Applies to SAML Assertion messages. Add a cloned unsigned copy of the Assertion before the existing Assertion.
- **XSW4**: Applies to SAML Assertion messages. Add a cloned unsigned copy of the Assertion within the existing Assertion.
- **XSW5**: Applies to SAML Assertion messages. Change a value in the signed copy of the Assertion and adds a copy of the original Assertion with the signature removed at the end of the SAML message.
- **XSW6**: Applies to SAML Assertion messages. Change a value in the signed copy of the Assertion and adds a copy of the original Assertion with the signature removed after the original signature.
- **XSW7**: Applies to SAML Assertion messages. Add an “Extensions” block with a cloned unsigned assertion.
- **XSW8**: Applies to SAML Assertion messages. Add an “Object” block containing a copy of the original assertion with the signature removed.
In the Github Enterprise vulnerability, this request would verify and create a sessions for `Attacker` instead of `Legitimate User`, even if `FA` is not signed.
### XML Comment Handling
A threat actor who already has authenticated access into a SSO system can authenticate as another user without that individual’s SSO password. This [vulnerability](https://www.bleepstatic.com/images/news/u/986406/attacks/Vulnerabilities/SAML-flaw.png) has multiple CVE in the following libraries and products.
- OneLogin - python-saml - CVE-2017-11427
- OneLogin - ruby-saml - CVE-2017-11428
- Clever - saml2-js - CVE-2017-11429
- OmniAuth-SAML - CVE-2017-11430
- Shibboleth - CVE-2018-0489
- Duo Network Gateway - CVE-2018-7340
Researchers have noticed that if an attacker inserts a comment inside the username field in such a way that it breaks the username, the attacker might gain access to a legitimate user's account.
An alternative exploitation would use `XML entities` to bypass the signature verification, since the content will not change, except during XML parsing.
The SAML response is accepted by the service provider. Due to the vulnerability, the service provider application reports "taf" as the value of the "uid" attribute.
- [Attacking SSO: Common SAML Vulnerabilities and Ways to Find Them - Jem Jensen - March 7, 2017](https://blog.netspi.com/attacking-sso-common-saml-vulnerabilities-ways-find/)
- [How to Hunt Bugs in SAML; a Methodology - Part I - Ben Risher (@epi052) - March 7, 2019](https://epi052.gitlab.io/notes-to-self/blog/2019-03-07-how-to-test-saml-a-methodology/)
- [How to Hunt Bugs in SAML; a Methodology - Part II - Ben Risher (@epi052) - March 13, 2019](https://epi052.gitlab.io/notes-to-self/blog/2019-03-13-how-to-test-saml-a-methodology-part-two/)
- [How to Hunt Bugs in SAML; a Methodology - Part III - Ben Risher (@epi052) - March 16, 2019](https://epi052.gitlab.io/notes-to-self/blog/2019-03-16-how-to-test-saml-a-methodology-part-three/)
- [On Breaking SAML: Be Whoever You Want to Be - Juraj Somorovsky, Andreas Mayer, Jorg Schwenk, Marco Kampmann, and Meiko Jensen - August 23, 2012](https://www.usenix.org/system/files/conference/usenixsecurity12/sec12-final91-8-23-12.pdf)
- [The road to your codebase is paved with forged assertions - Ioannis Kakavas (@ilektrojohn) - March 13, 2017](http://www.economyofmechanism.com/github-saml)
- [Truncation of SAML Attributes in Shibboleth 2 - redteam-pentesting.de - January 15, 2018](https://www.redteam-pentesting.de/de/advisories/rt-sa-2017-013/-truncation-of-saml-attributes-in-shibboleth-2)
