@incollection{PoddebniakDresenMuelleretal.2018, author = {Poddebniak, Damian and Dresen, Christian and M{\"u}ller, Jens and Ising, Fabian and Schinzel, Sebastian and Friedberg, Simon and Somorovsky, Juraj and Schwenk, J{\"o}rg}, title = {Efail: Breaking S/MIME and OpenPGP Email Encryption using Exfiltration Channels}, series = {USENIX Security 2018}, booktitle = {USENIX Security 2018}, edition = {27th}, address = {Baltimore, MD, USA}, isbn = {978-1-931971-46-1}, year = {2018}, 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{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{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{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} } @article{WillingDresenGerlitzetal.2021, author = {Willing, Markus and Dresen, Christian and Gerlitz, Eva and Haering, Maximilian and Smith, Matthew and Binnewies, Carmen and Guess, Tim and Haverkamp, Uwe and Schinzel, Sebastian}, title = {Behavioral responses to a cyber attack in a hospital environment}, series = {Nature -- Scientific Reports}, journal = {Nature -- Scientific Reports}, doi = {10.1038/s41598-021-98576-7}, year = {2021}, abstract = {Technical and organizational steps are necessary to mitigate cyber threats and reduce risks. Human behavior is the last line of defense for many hospitals and is considered as equally important as technical security. Medical staff must be properly trained to perform such procedures. This paper presents the first qualitative, interdisciplinary research on how members of an intermediate care unit react to a cyberattack against their patient monitoring equipment. We conducted a simulation in a hospital training environment with 20 intensive care nurses. By the end of the experiment, 12 of the 20 participants realized the monitors' incorrect behavior. We present a qualitative behavior analysis of high performing participants (HPP) and low performing participants (LPP). The HPP showed fewer signs of stress, were easier on their colleagues, and used analog systems more often than the LPP. With 40\% of our participants not recognizing the attack, we see room for improvements through the use of proper tools and provision of adequate training to prepare staff for potential attacks in the future.}, language = {en} } @inproceedings{KaspereitOendaroeLuvizottoCesaretal.2024, author = {Kaspereit, Jonas and {\"O}ndar{\"o}, Gurur and Luvizotto Cesar, Gustavo and Ebbers, Simon and Ising, Fabian and Saatjohann, Christoph and Jonker, Mattijs and Holz, Ralph and Schinzel, Sebastian}, title = {LanDscAPe: Exploring LDAP Weaknesses and Data Leaks at Internet Scale}, series = {33rd USENIX Security Symposium (USENIX Security 24)}, booktitle = {33rd USENIX Security Symposium (USENIX Security 24)}, isbn = {978-1-939133-44-1}, doi = {10.25974/fhms-18157}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-181577}, year = {2024}, abstract = {The Lightweight Directory Access Protocol (LDAP) is the standard technology to query information stored in directories. These directories can contain sensitive personal data such as usernames, email addresses, and passwords. LDAP is also used as a central, organization-wide storage of configuration data for other services. Hence, it is important to the security posture of many organizations, not least because it is also at the core of Microsoft's Active Directory, and other identity management and authentication services. We report on a large-scale security analysis of deployed LDAP servers on the Internet. We developed LanDscAPe, a scanning tool that analyzes security-relevant misconfigurations of LDAP servers and the security of their TLS configurations. Our Internet-wide analysis revealed more than 10k servers that appear susceptible to a range of threats, including insecure configurations, deprecated software with known vulnerabilities, and insecure TLS setups. 4.9k LDAP servers host personal data, and 1.8k even leak passwords. We document, classify, and discuss these and briefly describe our notification campaign to address these concerning issues.}, language = {en} } @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} }