@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{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} } @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{SaatjohannIsingKringsetal.2020, author = {Saatjohann, Christoph and Ising, Fabian and Krings, Luise and Schinzel, Sebastian}, title = {STALK: security analysis of smartwatches for kids}, series = {ARES 2020: The 15th International Conference on Availability, Reliability and Security / Editors: Melanie Volkamer, Christian Wressnegger}, booktitle = {ARES 2020: The 15th International Conference on Availability, Reliability and Security / Editors: Melanie Volkamer, Christian Wressnegger}, isbn = {978-1-4503-8833-7}, doi = {10.1145/3407023.3407037}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-123548}, pages = {1 -- 10}, year = {2020}, abstract = {Smart wearable devices become more and more prevalent in the age of the Internet of Things. While people wear them as fitness trackers or full-fledged smartphones, they also come in unique versions as smartwatches for children. These watches allow parents to track the location of their children in real-time and offer a communication channel between parent and child. In this paper, we analyzed six smartwatches for children and the corresponding backend platforms and applications for security and privacy concerns. We structure our analysis in distinct attacker scenarios and collect and describe related literature outside academic publications. Using a cellular network Man-in-the-Middle setup, reverse engineering, and dynamic analysis, we found several severe security issues, allowing for sensitive data disclosure, complete watch takeover, and illegal remote monitoring functionality.}, language = {en} } @article{GierlingSaatjohannDresenetal.2020, author = {Gierling, Markus and Saatjohann, Christoph and Dresen, Christian and K{\"o}be, Julia and Rath, Benjamin and Eckardt, Lars and Schinzel, Sebastian}, title = {Reviewing Cyber Security Research of Implantable Medical Rhythm Devices regarding Patients' Risk}, series = {86. Jahrestagung und Herztage 2020 der DGK}, volume = {Band 109, Supplement 1, April 2020}, journal = {86. Jahrestagung und Herztage 2020 der DGK}, doi = {10.1007/s00392-020-01621-0}, pages = {1 -- 2}, year = {2020}, abstract = {Introduction: The recent publication of several critical cyber security issues in cardiac implantable devices and the resulting press coverage upsets affected users and their trust in medical device producers. Reviewing the published security vulnerabilities regarding networked medical devices, it raises the question, if the reporting media, the responsible security researchers, and the producers handle security vulnerabilities appropriately. Are the media reports of security vulnerabilities in medical devices meaningful in a way that patients can assess their respective risk for an attack via the security vulnerability? The collaboration between IT-security experts and clinicians aims at reviewing published security vulnerabilities of rhythm devices, and evaluate overall patients risks. Methodology: We performed a literature review on security vulnerabilities in implantable medical devices with a focus on cardiac devices. We analyzed (Fig. 1) the (1) requirements for an attacker and the (2) technical feasibility and clustered them in three different scenarios: The first scenario requires that the attacker physically approaches a victim with a programming device. The second scenario requires proximity to the victim, e.g., within a few meters. The third and strongest attacker scenario is a remote attack that doesn't require any physical proximity to the victim. We then compare the attacker scenarios and (3) the overall patients' risks with the press coverage (overhyped, adequate, underhyped). (4) The resulting overall patients' risk was rated by clinicians (security vulnerability of patients' data, dangerous programming possible). Results: Out of the three analyzed incidents, we found one to be underhyped, one to be overhyped, and one was appropriate compared to the medial coverage (Fig. 2). The most occurring technical issues were based on the absence of basic security primitives. The patient damage for all of the analyzed incidents was fatal in the worst-case scenario. Further, the patient damage and the overall patient risks are disjunct due to the missing capability of performing large scale attacks. Conclusion: The resulting overall patients' risks may not adequately reflect the patient damage in the considered cases. Often, the overall patient risk is not as severe as the necessary attacker capabilities are high and it would require strongly motivated attackers to perform the attack. Therefore, most of the reviewed cases are considered with a smaller overall patient risk than implied by press reports. Reviewing the ongoing IT-Security trends regarding implantable medical devices shows an increasing focus on researching in the field of medical device security. Therefore, further findings in the near future are to be expected. To deal with this fact in a responsible way, proper proactive knowledge management is mandatory. We recommend medical staff to critically reflect reports in mass media due to possible sensationalism. Therefore, we propose a joint approach in combining the technical expertise of cyber security experts with clinical aspects of medical experts, to ensure a solid understanding of a newly published vulnerability. The combination of both communities promises to result in better predictions for patients' risks from security vulnerabilities in implanted cardiac devices.}, 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{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{WillingDresenHaverkampetal.2020, author = {Willing, Markus and Dresen, Christian and Haverkamp, Uwe and Schinzel, Sebastian}, title = {Analyzing medical device connectivity and its effect on cyber security in german hospitals}, publisher = {BMC Medical Informatics and Decision Making volume}, doi = {10.1186/s12911-020-01259-y}, year = {2020}, abstract = {Background: Modern healthcare devices can be connected to computer networks and many western healthcareinstitutions run those devices in networks. At the same time, cyber attacks are on the rise and there is evidence thatcybercriminals do not spare critical infrastructure such as major hospitals, even if they endanger patients. Intuitively,the more and closer connected healthcare devices are to public networks, the higher the risk of getting attacked. Methods: To asses the current connectivity status of healthcare devices, we surveyed the field of German hospitalsand especially University Medical Center UMCs. Results: The results show a strong correlation between the networking degree and the number of medical devices.The average number of medical devices is 25.150, with a median of networked medical devices of 3.600. Actual keyusers of networked medical devices are the departments Radiology, Intensive Care, Radio-Oncology RO, NuclearMedicine NUC, and Anaesthesiology in the group of UMCs. In the next five years, the usage of networked medicaldevices will increase significantly in the departments of Surgery, Intensive Care, and Radiology. We detected a strongcorrelation between the degree of connectivity and the likelihood of being attacked.The survey answers regarding the cyber security status reveal a lack of security basics in some of the inquiredhospitals. We did discover successful attacks in hospitals with separated or subsidiary departments. A fusion ofcompetencies on an organizational level facilitates the right behavior here. Most hospitals rated themselvespredominantly positively in the self-assessment but also stated the usefulness of IT security insurance.Conclusions:Concluding our results, hospitals are already facing the consequences of omitted measures within theirgrowing pool of medical devices. Continuously relying on historically grown structures without adaption and trustingmanufactures to solve vectors is a critical behavior that could seriously endanger patients.}, language = {en} }