@inproceedings{DresenIsingPoddebniaketal.2020, author = {Dresen, Christian and Ising, Fabian and Poddebniak, Damian and Kappert, Tobias and Holz, Thorsten and Schinzel, Sebastian}, title = {CORSICA: Cross-Origin Web Service Identification}, series = {The 15th ACM ASIA Conference on Computer and Communications Security}, booktitle = {The 15th ACM ASIA Conference on Computer and Communications Security}, editor = {Zhou, Jianying}, year = {2020}, abstract = {Vulnerabilities in private networks are difficult to detect for attackers outside of the network. While there are known methods for port scanning internal hosts that work by luring unwitting internal users to an external web page that hosts malicious JavaScript code, no such method for detailed and precise service identification is known. The reason is that the Same Origin Policy (SOP) prevents access to HTTP responses of other origins by default. We perform a structured analysis of loopholes in the SOP that can be used to identify web applications across network boundaries. For this, we analyze HTML5, CSS, and JavaScript features of standard-compliant web browsers that may leak sensitive information about cross-origin content. The results reveal several novel techniques, including leaking JavaScript function names or styles of cross-origin requests that are available in all common browsers. We implement and test these techniques in a tool called CORSICA. It can successfully identify 31 of 42 (74\%) of web services running on different IoT devices as well as the version numbers of the four most widely used content management systems WordPress, Drupal, Joomla, and TYPO3. CORSICA can also determine the patch level on average down to three versions (WordPress), six versions (Drupal), two versions (Joomla), and four versions (TYPO3) with only ten requests on average. Furthermore, CORSICA is able to identify 48 WordPress plugins containing 65 vulnerabilities. Finally, we analyze mitigation strategies and show that the proposed but not yet implemented strategies Cross-Origin Resource Policy (CORP)} and Sec-Metadata would prevent our identification techniques.}, language = {en} } @inproceedings{EbbersIsingSaatjohannetal.2021, author = {Ebbers, Simon and Ising, Fabian and Saatjohann, Christoph and Schinzel, Sebastian}, title = {Grand Theft App: Digital Forensics of Vehicle Assistant Apps}, series = {ARES 2021: The 16th International Conference on Availability, Reliability and Security}, booktitle = {ARES 2021: The 16th International Conference on Availability, Reliability and Security}, doi = {10.1145/3465481.3465754}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-139031}, year = {2021}, abstract = {Due to the increasing connectivity of modern vehicles, collected data is no longer only stored in the vehicle itself but also transmitted to car manufacturers and vehicle assistant apps. This development opens up new possibilities for digital forensics in criminal investigations involving modern vehicles. This paper deals with the digital forensic analysis of vehicle assistant apps of eight car manufacturers. We reconstruct the driver's activities based on the data stored on the smartphones and in the manufacturer's backend. For this purpose, data of the Android and iOS apps of the car manufacturers Audi, BMW, Ford, Mercedes, Opel, Seat, Tesla, and Volkswagen were extracted from the smartphone and examined using digital forensic methods following forensics guidelines. Additionally, manufacturer data was retrieved using Subject Access Requests. Using the extensive data gathered, we reconstruct trips and refueling processes, determine parking positions and duration, and track the locking and unlocking of the vehicle. Our findings show that the digital forensic investigation of smartphone applications is a useful addition to vehicle forensics and should therefore be taken into account in the strategic preparation of future digital forensic investigations.}, language = {en} } @inproceedings{GierlingDresenEichetal.2018, author = {Gierling, Markus and Dresen, Christian and Eich, Hans and Mittman, Karin and Schinzel, Sebastian and Haverkamp, Uwe}, title = {Analysis and consequences of an imaging process concerning the cyber security of a networked computer tomography scanner}, series = {STRAHLENTHERAPIE UND ONKOLOGIE}, booktitle = {STRAHLENTHERAPIE UND ONKOLOGIE}, pages = {185 -- 186}, year = {2018}, language = {en} } @inproceedings{IsingPoddebniakKappertetal.2023, author = {Ising, Fabian and Poddebniak, Damian and Kappert, Tobias and Saatjohann, Christoph and Schinzel, Sebastian}, title = {Content-Type: multipart/oracle -- Tapping into Format Oracles in Email End-to-End Encryption}, series = {32nd USENIX Security Symposium}, booktitle = {32nd USENIX Security Symposium}, publisher = {USENIX Association}, year = {2023}, abstract = {S/MIME and OpenPGP use cryptographic constructions repeatedly shown to be vulnerable to format oracle attacks in protocols like TLS, SSH, or IKE. However, format oracle attacks in the End-to-End Encryption (E2EE) email setting are considered impractical as victims would need to open many attacker-modified emails and communicate the decryption result to the attacker. But is this really the case? In this paper, we survey how an attacker may remotely learn the decryption state in email E2EE. We analyze the interplay of MIME and IMAP and describe side-channels emerging from network patterns that leak the decryption status in Mail User Agents (MUAs). Concretely, we introduce specific MIME trees that produce decryption-dependent net work patterns when opened in a victim's email client. We survey 19 OpenPGP- and S/MIME-enabled email clients and four cryptographic libraries and uncover a side-channel leaking the decryption status of S/MIME messages in one client. Further, we discuss why the exploitation in the other clients is impractical and show that it is due to missing feature support and implementation quirks. These unintended defenses create an unfortunate conflict between usability and security. We present more rigid countermeasures for MUA developers and the standards to prevent exploitation.}, language = {en} } @inproceedings{MayerPoddebniakFischeretal.2022, author = {Mayer, Peter and Poddebniak, Damian and Fischer, Konstantin and Brinkmann, Marcus and Somorovsky, Juraj and Schinzel, Sebastian and Volkamer, Melanie}, title = {"I don't know why I check this...'' - Investigating Expert Users' Strategies to Detect Email Signature Spoofing Attacks}, series = {Eighteenth Symposium on Usable Privacy and Security (SOUPS 2022)}, booktitle = {Eighteenth Symposium on Usable Privacy and Security (SOUPS 2022)}, publisher = {USENIX Association}, address = {Boston, MA}, isbn = {978-1-939133-30-4}, pages = {77 -- 96}, year = {2022}, abstract = {OpenPGP is one of the two major standards for end-to-end email security. Several studies showed that serious usability issues exist with tools implementing this standard. However, a widespread assumption is that expert users can handle these tools and detect signature spoofing attacks. We present a user study investigating expert users' strategies to detect signature spoofing attacks in Thunderbird. We observed 25 expert users while they classified eight emails as either having a legitimate signature or not. Studying expert users explicitly gives us an upper bound of attack detection rates of all users dealing with PGP signatures. 52\% of participants fell for at least one out of four signature spoofing attacks. Overall, participants did not have an established strategy for evaluating email signature legitimacy. We observed our participants apply 23 different types of checks when inspecting signed emails, but only 8 of these checks tended to be useful in identifying the spoofed or invalid signatures. In performing their checks, participants were frequently startled, confused, or annoyed with the user interface, which they found supported them little. All these results paint a clear picture: Even expert users struggle to verify email signatures, usability issues in email security are not limited to novice users, and developers may need proper guidance on implementing email signature GUIs correctly.}, language = {en} } @inproceedings{MuellerBrinkmannPoddebniaketal.2019, author = {M{\"u}ller, Jens and Brinkmann, Marcus and Poddebniak, Damian and B{\"o}ck, Hanno and Schinzel, Sebastian and Smomrosvsky, Juraj and Schwenk, J{\"o}rg}, title = {"Johnny, you are fired!" - Spoofing OpenPGP and S/MIME Signatures in Emails}, series = {28th Usenix Security Symposium, Santa Clara, CA, USA}, booktitle = {28th Usenix Security Symposium, Santa Clara, CA, USA}, year = {2019}, abstract = {OpenPGP and S/MIME are the two major standards to en-crypt and digitally sign emails. Digital signatures are sup-posed to guarantee authenticity and integrity of messages. Inthis work we show practical forgery attacks against variousimplementations of OpenPGP and S/MIME email signatureverification in five attack classes: (1) We analyze edge casesin S/MIME's container format. (2) We exploit in-band sig-naling in the GnuPG API, the most widely used OpenPGPimplementation. (3) We apply MIME wrapping attacks thatabuse the email clients' handling of partially signed mes-sages. (4) We analyze weaknesses in the binding of signedmessages to the sender identity. (5) We systematically testemail clients for UI redressing attacks.Our attacks allow the spoofing of digital signatures for ar-bitrary messages in 14 out of 20 tested OpenPGP-capableemail clients and 15 out of 22 email clients supportingS/MIME signatures. While the attacks do not target the un-derlying cryptographic primitives of digital signatures, theyraise concerns about the actual security of OpenPGP andS/MIME email applications. Finally, we propose mitigationstrategies to counter these attacks.}, language = {de} } @inproceedings{MuellerBrinkmannPoddebniaketal.2019, author = {M{\"u}ller, Jens and Brinkmann, Marcus and Poddebniak, Damian and Schinzel, Sebastian and Schwenk, J{\"o}rg}, title = {What's up John­ny? - Co­vert Con­tent At­tacks on Email End-to-End En­cryp­ti­on}, series = {17th In­ter­na­tio­nal Con­fe­rence on Ap­p­lied Cryp­to­gra­phy and Net­work Se­cu­ri­ty (ACNS 2019)}, booktitle = {17th In­ter­na­tio­nal Con­fe­rence on Ap­p­lied Cryp­to­gra­phy and Net­work Se­cu­ri­ty (ACNS 2019)}, pages = {1 -- 18}, year = {2019}, abstract = {We show practical attacks against OpenPGP and S/MIMEencryption and digital signatures in the context of email. Instead of tar-geting the underlying cryptographic primitives, our attacks abuse legiti-mate features of the MIME standard and HTML, as supported by emailclients, to deceive the user regarding the actual message content. Wedemonstrate how the attacker can unknowingly abuse the user as a de-cryption oracle by replying to an unsuspicious looking email. Using thistechnique, the plaintext of hundreds of encrypted emails can be leakedat once. Furthermore, we show how users could be tricked into signingarbitrary text by replying to emails containing CSS conditional rules.An evaluation shows that "out of" OpenPGP-capable email clients,as well as "out of" clients supporting S/MIME, are vulnerable to atleast one attack. We provide different countermeasures and discuss theiradvantages and disadvantages.}, language = {de} } @inproceedings{MuellerBrinkmannPoddebniaketal.2020, author = {M{\"u}ller, Jens and Brinkmann, Marcus and Poddebniak, Damian and Schinzel, Sebastian and Schwenk, J{\"o}rg}, title = {Mailto: Me Your Secrets. On Bugs and Features in Email End-to-End Encryption}, series = {2020 IEEE Conference on Communications and Network Security (CNS)}, booktitle = {2020 IEEE Conference on Communications and Network Security (CNS)}, doi = {10.1109/CNS48642.2020.9162218}, pages = {1 -- 9}, year = {2020}, abstract = {OpenPGP and S/MIME are the two major standards for email end-to-end encryption. We show practical attacks against both encryption schemes in the context of email. First, we present a design flaw in the key update mechanism, allowing a third party to deploy a new key to the communication partners. Second, we show how email clients can be tricked into acting as an oracle for decryption or signing by exploiting their functionality to auto-save drafts. Third, we demonstrate how to exfiltrate the private key, based on proprietary mailto parameters implemented by various email clients. An evaluation shows that 8 out of 20 tested email clients are vulnerable to at least one attack. While our attacks do not target the underlying cryptographic primitives, they raise concerns about the practical security of OpenPGP and S/MIME email applications. Finally, we propose countermeasures and discuss their advantages and disadvantages.}, language = {de} } @inproceedings{MuellerIsingMla­de­novetal.2020, author = {M{\"u}ller, Jens and Ising, Fabian and Mla­de­nov, Vla­dis­lav and Mainka, Chris­ti­an and Schinzel, Sebastian and Schwenk, J{\"o}rg}, title = {Of­fice Do­cu­ment Se­cu­ri­ty and Pri­va­cy}, series = {14th USE­NIX Work­shop on Of­fen­si­ve Tech­no­lo­gies (WOOT 2020)}, booktitle = {14th USE­NIX Work­shop on Of­fen­si­ve Tech­no­lo­gies (WOOT 2020)}, publisher = {USENIX}, year = {2020}, abstract = {OOXML and ODF are the de facto standard data formats for word processing, spreadsheets, and presentations. Both are XML-based, feature-rich container formats dating back to the early 2000s. In this work, we present a systematic analysis of the capabilities of malicious office documents. Instead of focusing on implementation bugs, we abuse legitimate features of the OOXML and ODF specifications. We categorize our attacks into five classes: (1) Denial-of-Service attacks affecting the host on which the document is processed. (2) Invasion of privacy attacks that track the usage of the document. (3) Information disclosure attacks exfiltrating personal data out of the victim's computer. (4) Data manipulation on the victim's system. (5) Code execution on the victim's machine. We evaluated the reference implementations - Microsoft Office and LibreOffice - and found both of them to be vulnerable to each tested class of attacks. Finally, we propose mitigation strategies to counter these attacks.}, language = {en} } @inproceedings{MuellerIsingMldadenovetal.2019, author = {M{\"u}ller, Jens and Ising, Fabian and Mldadenov, Vladislav and Mainka, Christian and Schinzel, Sebastian and Schwenk, J{\"o}rg}, title = {Practical Decryption exFiltration: Breaking PDF Encryption}, series = {The 26th ACM Conference on Computer and Communications, Security (CCS 2019), London, United Kingdom}, booktitle = {The 26th ACM Conference on Computer and Communications, Security (CCS 2019), London, United Kingdom}, doi = {10.1145/3319535.3354214}, year = {2019}, abstract = {The Portable Document Format, better known as PDF, is one of themost widely used document formats worldwide, and in order to en-sure information confidentiality, this file format supports documentencryption. In this paper, we analyze PDF encryption and showtwo novel techniques for breaking the confidentiality of encrypteddocuments. First, we abuse the PDF feature ofpartially encrypteddocuments to wrap the encrypted part of the document withinattacker-controlled content and therefore, exfiltrate the plaintextonce the document is opened by a legitimate user. Second, we abusea flaw in the PDF encryption specification to arbitrarily manipulateencrypted content. The only requirement is that a single block ofknown plaintext is needed, and we show that this is fulfilled bydesign. Our attacks allow the recovery of the entire plaintext of en-crypted documents by using exfiltration channels which are basedon standard compliant PDF properties.We evaluated our attacks on 27 widely used PDF viewers andfound all of them to be vulnerable. We responsibly disclosed thevulnerabilities and supported the vendors in fixing the issue}, language = {en} }