Vladislav Mladenov

Your Software at my Service: Security Analysis of SaaS Single Sign-On Solutions in the Cloud

Software-as-a-Service (SaaS) is typically defined as a rental model for using a complex software product, running on a centralized computing platform, using a thin client (most frequently a web browser). As such, it is one of the major categories of Cloud Computing, besides IaaS and PaaS. While there are many economic benefits in using SaaS, each company must nevertheless enforce control over its own data processed in the Cloud. One of the most important building blocks of such an enforcement scheme is idM, whereat the industry standard for idM is SAML, the Security Assertion Markup Language. In this paper, we study the security of the SAML implementations of 22 CPs and show that 90% of them can be broken, resulting in company data exposure to attackers on the Internet. The detected vulnerabilities are exploited by a wide variety of attack techniques, ranging from classical web attacks to problems specific to XML processing.

Do Not Trust Me: Using Malicious IdPs for Analyzing and Attacking Single Sign-on

Single Sign-On (SSO) systems simplify login procedures by using an Identity Provider (IdP) to issue authentication tokens which can be consumed by Service Providers (SPs). Traditionally, IdPs are modeled as trusted third parties. This is reasonable for centralized SSO systems like Kerberos, where each SP explicitly specifies which single IdP it trusts. However, a typical use case for SPs like Salesforce is that each customer is allowed to configure his own IdP. A malicious IdP should however only be able to compromise the security of those accounts on the SP for which it was configured. If different accounts can be compromised, this must be considered as a serious attack. Additionally, in open systems like OpenID and OpenID Connect, the IdP for each customer account is dynamically detected in a discovery phase. Our research goal was to test if this phase can be used to trick a SP into using a malicious IdP for legitimate user accounts. Thus, by introducing a malicious IdP we evaluate in detail the popular and widely deployed SSO protocol OpenID. We found two novel classes of attacks, ID Spoofing (IDS) and Key Confusion (KC), on OpenID, which were not covered by previous research. Both attack classes allow compromising the security of all accounts on a vulnerable SP, even if those accounts were not allowed to use the malicious IdP. As a result, we were able to compromise 12 out the most popular 17 existing OpenID implementations, including Sourceforge, Drupal, ownCloud and JIRA. We developed an open source tool OpenID Attacker, which enables the fully automated and fine granular testing of OpenID implementations. Our research helps to better understand the message flow in the OpenID protocol, trust assumptions in the different components of the system, and implementation issues in OpenID components. All OpenID implementations have been informed about their vulnerabilities and we supported them in fixing the issues. One year after our reports, we have evaluated 70 online websites. Some of them have upgraded their libraries and were safe from our attacks, but 26% were still vulnerable.

Guardians of the Clouds: When Identity Providers Fail

Many cloud-based services offer interfaces to Single Sign-On (SSO) systems. This helps companies and Internet users to keep control over their data: By using an Identity Provider (IdP), they are able to enforce various access control strategies (e.g., RBAC) on data processed in the cloud. On the other hand, IdPs provide a valuable single point of attack: If the IdP can be compromised, all cloud services are affected, including well-protected applications such as Google Apps and Salesforce. This increases the impact of the attack by several orders of magnitude. In this paper, we analyze the security of six real-world SAML-based IdPs (OneLogin, Okta, WSO2 Stratos, Cloudseal, SSOCircle, and Bitium) which are used to protect cloud services. We present a novel attack technique (ACS Spoofing), which allows the adversary to successfully impersonate the victim in four of these SSO systems. To complete our survey on IdP security, we additionally evaluated the security of these six IdPs against well-known web attacks, and we were successful against four of them. In summary, we were able to break all six SSO systems. We present a online penetration test tool, ACSScanner, which is able to detect ACS Spoofing vulnerabilities on arbitrary IdPs. Additionally, we discuss several countermeasures for each attack type, ranging from simple whitelisting to the signing of authentication requests, and from anti-CSRF tokens and HTTP-Only cookies to cookie-TLS-bindings. We have implemented a combination of two advanced countermeasures.

Options for integrating eID and SAML

Several European countries currently introduce highly sophisticated eID functionality in their national identity cards. This functionality typically has no direct relation to web security standards, but will be integrated with web technologies to enable browser-based access to critical resources. The research challenge to combine eID protocols and web standards like TLS in a secure way proves extremely challenging: The security of many of the proposed systems boils down to HTTP session cookies and TLS server certificates. Therefore, the overall security is not improved and does not justify the additional costs. In this paper, we investigate this security challenge for the German national identity card and its eID functionality. We show that the solution currently standardized by the German government does not offer any additional security, by giving an in-depth analysis of the complete software system. We discuss several possible paths to an enhanced solution based on TLS channel bindings. Finally, we describe a system setup based on the SAML Holder-of-Key Web Browser Profile, which also mitigates interoperability problems.

SoK: Exploiting Network Printers

The idea of a paperless office has been dreamed of for more than three decades. However, nowadays printers are still one of the most essential devices for daily work and common Internet users. Instead of removing them, printers evolved from simple devices into complex network computer systems, installed directly into company networks, and carrying considerable confidential data in their print jobs. This makes them to an attractive attack target. In this paper we conduct a large scale analysis of printer attacks and systematize our knowledge by providing a general methodology for security analyses of printers. Based on our methodology, we implemented an open-source tool called PRinter Exploitation Toolkit (PRET). We used PRET to evaluate 20 printer models from different vendors and found all of them to be vulnerable to at least one of the tested attacks. These attacks included, for example, simple DoS attacks or skilled attacks, extracting print jobs and system files. On top of our systematic analysis we reveal novel insights that enable attacks from the Internet by using advanced cross-site printing techniques, combined with printer CORS spoofing. Finally, we show how to apply our attacks to systems beyond typical printers like Google Cloud Print or document processing websites.

SoK: Single Sign-On Security — An Evaluation of OpenID Connect

OpenID Connect is the OAuth 2.0-based replacement for OpenID 2.0 (OpenID) andone of the most important Single Sign-On (SSO) protocols used for delegatedauthentication. It is used by companies like Amazon, Google, Microsoft, andPayPal. In this paper, we systematically analyze well-known attacks on SSOprotocols and adapt these on OpenID Connect. Additionally, we introduce twonovel attacks on OpenID Connect, Identity Provider Confusion and MaliciousEndpoints Attack, abusing flaws in the current specification and breaking thesecurity goals of the protocol. In 2014 we communicated with the authors of theOpenID Connect specification about these attacks and helped to repair the issue(currently an RFC Draft). We categorize the described attacks into two classes: Single-Phase Attacksabusing a lack of a single security check and Cross-Phase Attacks requiring acomplex attack setup and manipulating multiple messages distributed across thewhole protocol workflow. We provide an evaluation of officially referencedOpenID Connect libraries and find 75% of them vulnerable to at least oneSingle-Phase Attack. All libraries are susceptible to Cross-Phase Attacks, which is not surprising since the attacks abuse a logic flaw in the protocoland not an implementation error. We reported the found vulnerabilities to thedevelopers and helped them to fix the issues. We address the existing problemsin a Practical Offensive Evaluation of Single Sign-On Services (PrOfESSOS). PrOfESSOS is our open source implementation for a fully automatedEvaluation-as-a-Service for SSO. PrOfESSOS introduces a generic approach toimprove the security of OpenID Connect implementations by system-aticallydetecting vulnerabilities. In collaboration with the IETF OAuth and OpenIDConnect working group, we integrate PrOfESSOS into the OpenID Connect certification process. PrOfESSOS is available at https://openid.sso-security.de.

PostScript Undead: Pwning the Web with a 35 Years Old Language.

PostScript is a Turing complete page description language dating back to 1982. It is supported by most laser printers and for a long time it had been the preferred file format for documents like academic papers. In this work, we show that popular services such as Wikipedia, Microsoft OneDrive, and Google Mail can be attacked using malicious PostScript code. Besides abusing legitimate features of the PostScript language, we systematically analyzed the security of the most popular PostScript interpreter – Ghostscript. Our attacks include information disclosure, file inclusion, and remote command execution. Furthermore, we present methods to obfuscate PostScript code and embed it within legitimate PDF files to bypass security filters. This allows us to create a hybrid exploit that can be used to attack web applications, clients systems, print servers, or printers. Our large-scale evaluation reveals that 56% of the analyzed web applications are vulnerable to at least one attack. In addition, three of the top 15 Alexa websites were found vulnerable. We provide different countermeasures and discuss their advantages and disadvantages. Finally, we extend the scope of our research considering further targets and more advanced obfuscation techniques.

On The (In-)Security Of JavaScript Object Signing And Encryption

JavaScript Object Notation (JSON) has evolved to the de-facto standard file format in the web used for application configuration, cross- and same-origin data exchange, as well as in Single Sign-On (SSO) protocols such as OpenID Connect. To protect integrity, authenticity, and confidentiality of sensitive data, JavaScript Object Signing and Encryption (JOSE) was created to apply cryptographic mechanisms directly in JSON messages. We investigate the security of JOSE and present different applicable attacks on several popular libraries. We introduce JOSEPH (JavaScript Object Signing and Encryption Pentesting Helper) -- our newly developed Burp Suite extension, which automatically performs security analysis on targeted applications. JOSEPHs automatic vulnerability detection ranges from executing simple signature exclusion or signature faking techniques, which neglect JSON message integrity, up to highly complex cryptographic Bleichenbacher attacks, breaking the confidentiality of encrypted JSON messages. We found severe vulnerabilities in six popular JOSE libraries. We responsibly disclosed all weaknesses to the developers and helped them to provide fixes.

SECRET: On the Feasibility of a Secure, Efficient, and Collaborative Real-Time Web Editor

Real-time editing tools like Google Docs, Microsoft Office Online, or Etherpad have changed the way of collaboration. Many of these tools are based on Operational Transforms (OT), which guarantee that the views of different clients onto a document remain consistent over time. Usually, documents and operations are exposed to the server in plaintext -- and thus to administrators, governments, and potentially cyber criminals. Therefore, it is highly desirable to work collaboratively on encrypted documents. Previous implementations do not unleash the full potential of this idea: They either require large storage, network, and computation overhead, are not real-time collaborative, or do not take the structure of the document into account. The latter simplifies the approach since only OT algorithms for byte sequences are required, but the resulting ciphertexts are almost four times the size of the corresponding plaintexts. We present SECRET, the first secure, efficient, and collaborative real-time editor. In contrast to all previous works, SECRET is the first tool that (1.) allows the encryption of whole documents or arbitrary sub-parts thereof, (2.) uses a novel combination of tree-based OT with a structure preserving encryption, and (3.) requires only a modern browser without any extra software installation or browser extension. We evaluate our implementation and show that its encryption overhead is three times smaller in comparison to all previous approaches. SECRET can even be used by multiple users in a low-bandwidth scenario. The source code of SECRET is published on GitHub as an open-source project:https://github.com/RUB-NDS/SECRET/