Single Sign-On (SSO) is an authentication process that allows users to access multiple services with a single set of login credentials. Although SSO improves the user experience, it poses challenges to developers to implement complex authentication protocols securely. External services, called brokers, simplify the integration of SSO. In this paper, we shed light on the emerging brokered SSO ecosystem, focusing on the security of the newly introduced actor, the broker. We systematically evaluate the landscape of brokered SSO, uncovering significant blind spots in previous research. Our study reveals that 25% of the websites with SSO integrate brokers for authentication, an area that has not been covered by any previous research. Through our comprehensive security evaluation, we identify three categories of threats associated with brokered SSO: (1) insufficient validation of redirect chains enabling injection attacks, (2) unauthorized data access enabling account takeovers, and (3) violations of security best current practices. We expose vulnerabilities in over 50 brokers, compromising the security of more than 2k websites. These findings represent only a lower bound of a critical situation, underscoring the urgent need for improved security measures and protocols to safeguard the integrity of brokered SSO systems.

Single Sign-On (SSO) with OAuth 2.0 and OpenID Connect 1.0 is essential for user authentication and autho-rization on the Internet. Billions of users rely on SSO services provided by Google, Facebook, and Apple. For large-scale measurements on the security of SSO, researchers need to reliably detect SSO implementations in the wild. In this paper, we survey the current state of 36 SSO measurement tools from prior work and discover gaps leading to blind spots in the SSO landscape that hinder the community from improving large-scale research. We observe unreliable measurements and a lack of reproducibility, making comparisons between studies difficult, if not impossible. We fill these gaps with SSO-MONITOR, our open-source, modular, and highly extensible framework for large-scale SSO landscape and security measurements. SSO-MONITOR achieves a high accuracy of 93% and, compared to pre-vious tools, significantly improves the reliability of SSO measurements by 19 %. It continuously takes snapshots of SSO implementations on the top 1M web sites to compose an SSO archive that is reproducible by design. Therefore, it passively monitors the SSO flows and provides an extensive set of landscape and security insights on sso-monitor.me. Our SSO archive allows researchers to perform comprehensive measurements over time and even beyond the scope of SSO. We use the data in our SSO archive to measure the security of 89k SSO authentication flows on the top 1M websites. Thereby, we discover 33k violations of OAuth Security Best Current Practices and 339 severe security vulnerabilities. They include 30 username and password leaks and 28 token leaks that allow full account takeovers.

3D printing is a well-established technology with rapidly increasing usage scenarios both in the industry and consumer context. The growing popularity of 3D printing has also attracted security researchers, who have analyzed possibilities for weakening 3D models or stealing intellectual property from 3D models. We extend these important aspects and provide the first comprehensive security analysis of 3D printing data formats. We performed our systematic study on the example of the 3D Manufacturing Format (3MF), which offers a large variety of features that could lead to critical attacks. Based on 3MF’s features, we systematized three attack goals: Data Exfiltration (dex), Denial of Service, and UI Spoofing (uis). We achieve these goals by exploiting the complexity of 3MF, which is based on the Open Packaging Conventions (OPC) format and uses XML to define 3D models. In total, our analysis led to 352 tests. To create and run these tests automatically, we implemented an open-source tool named 3MF Analyzer (tool), which helped us evaluate 20 applications.

Single Sign-On (SSO) protocols like OAuth 2.0 and OpenID Connect 1.0 are cornerstones of modern web security, and have received much academic attention. Users sign in at a trusted Identity Provider (IdP) that subsequently allows many Service Providers (SPs) to verify the users' identities. Previous research concentrated on the standardized - called textbook SSO in this paper - authentication flows, which rely on HTTP redirects to transfer identity tokens between the SP and IdP. However, modern web applications like single page apps may not be able to execute the textbook flow because they lose the local state in case of HTTP redirects. By using novel browser technologies, such as postMessage, developers designed and implemented SSO protocols that were neither documented nor analyzed thoroughly. We call them dual-window SSO flows.

The Portable Document Format (PDF) is the de-facto standard for document exchange. The PDF specification defines two different types of digital signatures to guarantee the authenticity and integrity of documents: approval signatures and certification signatures. Approval signatures testify one specific state of the PDF document. Their security has been investigated at CCS’19. Certification signatures are more powerful and flexible. They cover more complex workflows, such as signing contracts by multiple parties. To achieve this goal, users can make specific changes to a signed document without invalidating the signature.This paper presents the first comprehensive security evaluation on certification signatures in PDFs. We describe two novel attack classes – Evil Annotation and Sneaky Signature attacks which abuse flaws in the current PDF specification. Both attack classes allow an attacker to significantly alter a certified document’s visible content without raising any warnings. Our practical evaluation shows that an attacker could change the visible content in 15 of 26 viewer applications by using Evil Annotation attacks and in 8 applications using Sneaky Signature by using PDF specification compliant exploits. We improved both attacks’ stealthiness with applications’ implementation issues and found only two applications secure to all attacks. On top, we show how to gain high privileged JavaScript execution in Adobe.We responsibly disclosed these issues and supported the vendors to fix the vulnerabilities. We also propose concrete countermeasures and improvements to the current specification to fix the issues.

The Portable Document Format, better known as PDF, is one of the most widely used document formats worldwide, and in order to ensure information confidentiality, this file format supports document encryption. In this paper, we analyze PDF encryption and show two novel techniques for breaking the confidentiality of encrypted documents. First, we abuse the PDF feature of partially encrypted documents to wrap the encrypted part of the document within attacker-controlled content and therefore, exfiltrate the plaintext once the document is opened by a legitimate user. Second, we abuse a flaw in the PDF encryption specification to arbitrarily manipulate encrypted content. The only requirement is that a single block of known plaintext is needed, and we show that this is fulfilled by design. Our attacks allow the recovery of the entire plaintext of encrypted documents by using exfiltration channels which are based on standard compliant PDF properties. We evaluated our attacks on 27 widely used PDF viewers and found all of them to be vulnerable. We responsibly disclosed the vulnerabilities and supported the vendors in fixing the issues.

The Portable Document Format (PDF) is the de-facto standard for document exchange worldwide. To guarantee the authenticity and integrity of documents, digital signatures are used. Several public and private services ranging from governments, public enterprises, banks, and payment services rely on the security of PDF signatures. In this paper, we present the first comprehensive security evaluation on digital signatures in PDFs. We introduce three novel attack classes which bypass the cryptographic protection of digitally signed PDF files allowing an attacker to spoof the content of a signed PDF. We analyzed 22 different PDF viewers and found 21 of them to be vulnerable, including prominent and widely used applications such as Adobe Reader DC and Foxit. We additionally evaluated eight online validation services and found six to be vulnerable. A possible explanation for these results could be the absence of a standard algorithm to verify PDF signatures -- each client verifies signatures differently, and attacks can be tailored to these differences. We, therefore, propose the standardization of a secure verification algorithm, which we describe in this paper. All findings have been responsibly disclosed, and the affected vendors were supported during fixing the issues. As a result, three generic CVEs for each attack class were issued [50-52]. Our research on PDF signatures and more information is also online available at https://www.pdf-insecurity.org/.

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.

OpenID Connect is the OAuth 2.0-based replacement for OpenID 2.0 (OpenID) and one of the most important Single Sign-On (SSO) protocols used for delegated authentication. It is used by companies like Amazon, Google, Microsoft, and PayPal. In this paper, we systematically analyze well-known attacks on SSO protocols and adapt these on OpenID Connect. Additionally, we introduce two novel attacks on OpenID Connect, Identity Provider Confusion and Malicious Endpoints Attack, abusing flaws in the current specification and breaking the security goals of the protocol. In 2014 we communicated with the authors of the OpenID 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 Attacks abusing a lack of a single security check and Cross-Phase Attacks requiring a complex attack setup and manipulating multiple messages distributed across the whole protocol workflow. We provide an evaluation of officially referenced OpenID Connect libraries and find 75% of them vulnerable to at least one Single-Phase Attack. All libraries are susceptible to Cross-Phase Attacks, which is not surprising since the attacks abuse a logic flaw in the protocol and not an implementation error. We reported the found vulnerabilities to the developers and helped them to fix the issues. We address the existing problems in a Practical Offensive Evaluation of Single Sign-On Services (PrOfESSOS). PrOfESSOS is our open source implementation for a fully automated Evaluation-as-a-Service for SSO. PrOfESSOS introduces a generic approach to improve the security of OpenID Connect implementations by systematically detecting 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.

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.

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.