Helmholtz Center for Information Security
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SENG, the SGX-Enforcing Network Gateway: Authorizing Communication from Shielded Clients
Get PDFNetwork administrators face a security-critical dilemma. While they want to tightly contain their hosts, they usually have to relax firewall policies to support a large variety of applications. However, liberal policies like this enable data exfiltration by unknown (and untrusted) client applications. An inability to attribute communication accurately and reliably to applications is at the heart of this problem. Firewall policies are restricted to coarse-grained features that are easy to evade and mimic, such as protocols or port numbers.
We present SENG, a network gateway that enables firewalls to reliably attribute traffic to an application. SENG shields an application in an SGX-tailored LibOS and transparently establishes an attestation-based DTLS channel between the SGX enclave and the central network gateway. Consequently, administrators can perfectly attribute traffic to its originating application, and thereby enforce fine-grained per-application communication policies at a central firewall. Our prototype implementation demonstrates that SENG (i) allows administrators to readily use their favorite firewall to enforce network policies on a certified per-application basis and (ii) prevents local system-level attackers from interfering with the shielded application's communication
Clone Detection in Secure Messaging: Improving Post-Compromise Security in Practice
Get PDFWe investigate whether modern messaging apps achieve the strong post-compromise security guarantees offered by their underlying protocols. In particular, we perform a black-box experiment in which a user becomes the victim of a clone attack; in this attack,the user’s full state (including identity keys) is compromised by an attacker who clones their device and then later attempts to impersonate them, using the app through its user interface.Our attack should be prevented by protocols that offer post-compromise security, and thus, by all apps that are based on Signal’s double-ratchet algorithm (for instance, the Signal app, WhatsApp,and Facebook Secret Conversations). Our experiments reveal that this is not the case: most deployed messaging apps fall far short of the security that their underlying mechanisms suggest. We conjecture that this security gap is a result of many apps trading security for usability, by tolerating certain forms of desynchronization. We show that the tolerance of desynchronization necessarily leads to loss of post-compromise security in the strict sense, but we also show that more security can be retained than is currently offered in practice. Concretely, we present a modified version of the double-ratchet algorithm that tolerates forms of desynchronization while still being able to detect cloning activity.Moreover, we formally analyze our algorithm using the Tamarin prover to show that it achieves the desired security properties
End User and Expert Perceptions of Threats and Potential Countermeasures
Get PDFExperts often design security and privacy technology with specific use cases and threat models in mind.
In practice however, end users are not aware of these
threats and potential countermeasures. Furthermore, misconceptions about the benefits and limitations of security
and privacy technology inhibit large-scale adoption by end
users. In this paper, we address this challenge and contribute
a qualitative study on end users’ and security experts’ perceptions of threat models and potential countermeasures. We
follow an inductive research approach to explore perceptions
and mental models of both security experts and end users.
We conducted semi-structured interviews with 8 security experts and 13 end users. Our results suggest that in contrast to
security experts, end users neglect acquaintances and friends
as attackers in their threat models. Our findings highlight
that experts value technical countermeasures whereas end
users try to implement trust-based defensive methods
Automatically Granted Permissions in Android apps: An Empirical Study on their Prevalence and on the Potential Threats for Privacy
Get PDFDevelopers continuously update their Android apps to keep up with competitors in the market. Such constant updates do not bother end users, since by default the Android platform automatically pushes the most recent compatible release on the device, unless there are major changes in the list of requested permissions that users have to explicitly grant. The lack of explicit user's approval for each application update, however, may lead to significant risks for the end user, as the new release may include new subtle behaviors which may be privacy-invasive. The introduction of permission groups in the Android permission model makes this problem even worse: if a user gives a single permission within a group, the application can silently request further permissions in this group with each update---without having to ask the user.
In this paper, we explain the threat that permission groups may pose for the privacy of Android users. We run an empirical study on 2,865,553 app releases, and we show that in a representative app store more than ~17% of apps request at least once in their lifetime new dangerous permissions that the operating system grants without any user's approval. Our analyses show that apps actually use over 56% of such automatically granted permissions, although most of their descriptions do not explicitly explain for what purposes. Finally, our manual inspection reveals clear abuses of apps that leak sensitive data such as user's accurate location, list of contacts, history of phone calls, and emails which are protected by permissions that the user never explicitly acknowledges
Deceptive Previews: A Study of the Link Preview Trustworthiness in Social Platforms
Get PDFSocial media has become a primary mean of content and information sharing, thanks to its speed and simplicity. In this scenario, link previews play the important role of giving a meaningful first glance to users, summarizing the content of the shared webpage within their title, description and image. In our work, we analyzed the preview-rendering process, observing how it is possible to misuse it to obtain benign-looking previews for malicious links. Concrete use-case of this research field is phishing and spam spread, considering targeted attacks in addition to large-scale campaigns.
We designed a set of experiments for 20 social media platforms including social networks and instant messenger applications and found out how most of the platforms follow their own preview design and format, sometimes providing partial information. Four of these platforms allow preview crafting so as to hide the malicious target even to a tech-savvy user, and we found that it is possible to create misleading previews for the remaining 16 platforms when an attacker can register their own domain. We also observe how 18 social media platforms do not employ active nor passive countermeasures against the spread of known malicious links or software, and that existing cross-checks on malicious URLs can be bypassed through client and server-side redirections. To conclude, we suggest seven recommendations covering the spectrum of our findings, to improve the overall preview-rendering mechanism and increase users’ overall trust in social media platforms
A Tale of Two Headers: A Formal Analysis of Inconsistent Click-Jacking Protection on the Web
Get PDFClick-jacking protection on the modern Web is commonly enforced via client-side security mechanisms for framing control, like the X-Frame-Options header (XFO) and Content Security Policy (CSP). Though these client-side security mechanisms are certainly useful and successful, delegating protection to web browsers opens room for inconsistencies in the security guarantees offered to users of different browsers. In particular, inconsistencies might arise due to the lack of support for CSP and the different implementations of the underspecified XFO header. In this paper, we formally study the problem of inconsistencies in framing control policies across different browsers and we implement an automated policy analyzer based on our theory, which we use to assess the state of click-jacking protection on the Web. Our analysis shows that 10% of the (distinct) framing control policies in the wild are inconsistent and most often do not provide any level of protection to at least one browser. We thus propose recommendations for web developers and browser vendors to mitigate this issue. Finally, we design and implement a server-side proxy to retrofit security in web applications
Security, Availability, and Multiple Information Sources: Exploring Update Behavior of System Administrators
Get PDFExperts agree that keeping systems up to date is a powerful
security measure. Previous work found that users sometimes
explicitly refrain from performing timely updates, e.g., due
to bad experiences which has a negative impact on end-user
security. Another important user group has been investigated
less extensively: system administrators, who are responsible
for keeping complex and heterogeneous system landscapes
available and secure.
In this paper, we sought to understand administrators’ behavior, experiences, and attitudes regarding updates in a corporate environment. Based on the results of an interview
study, we developed an online survey and quantified common
practices and obstacles (e.g., downtime or lack of information
about updates). The findings indicate that even experienced
administrators struggle with update processes as the consequences of an update are sometimes hard to assess. Therefore,
we argue that more usable monitoring and update
Learning Input Tokens for Effective Fuzzing
Get PDFModern fuzzing tools like AFL operate at a lexical level: They explore the input space of tested programs one byte after another. For inputs with complex syntactical properties, this is very inefficient, as keywords and other tokens have to be composed one character at a time. Fuzzers thus allow to specify dictionaries listing possible tokens the input can be composed from; such dictionaries speed up fuzzers dramatically. Also, fuzzers make use of dynamic tainting to track input tokens and infer values that are expected in the input validation phase. Unfortunately, such tokens are usually implicitly converted to program specific values which causes a loss of the taints attached to the input data in the lexical phase.
In this paper we present a technique to extend dynamic tainting to not only track explicit data flows but also taint implicitly converted data without suffering from taint explosion. This extension makes it possible to augment existing techniques and automatically infer a set of tokens and seed inputs for the input language of a program given nothing but the source code. Specifically targeting the lexical analysis of an input processor, our lFuzzer test generator systematically explores branches of the lexical analysis, producing a set of tokens that fully cover all decisions seen. The resulting set of tokens can be directly used as a dictionary for fuzzing. Along with the token extraction seed inputs are generated which give further fuzzing processes a head start. In our experiments, the lFuzzer-AFL combination achieves up to 17% more coverage on complex input formats like JSON, LISP, tinyC, and JavaScript compared to AFL
Minting Mechanisms for (PoS) Blockchains
Get PDFPermissionless blockchain systems, such as Bitcoin, rely on users using their computational power to solve a puzzle in order to achieve a consensus. To incentivise users in
maintaining the system, newly minted coins are assigned to the user who solves this puzzle.
A hardware race that has hence ensued among the users, has had a detrimental impact on
the environment, with enormous energy consumption and increased global carbon footprint.
On the other hand, proof of stake systems incentivise coin hoarding as players maximise
their utility by holding their stakes. As a result, existing cryptocurrencies do not mimic the
day-to-day usability of a fiat currency, but are rather regarded as crypto-assets or investment
vectors.
In this work we initiate the study of minting mechanisms in cryptocurrencies as a primitive on its own right, and as a solution to prevent coin hoarding we propose a novel minting
mechanism based on waiting-time first-price auctions. Our main technical tool is a protocol to run an auction over any blockchain. Moreover, our protocol is the first to securely
implement an auction without requiring a semi-trusted party, i.e., where every miner in the
network is a potential bidder. Our approach is generically applicable and we show that it
is incentive-compatible with the underlying blockchain, i.e., the best strategy for a player is
to behave honestly. Our proof-of-concept implementation shows that our system is efficient
and scales to tens of thousands of bidders
Padding Ain’t Enough: Assessing the Privacy Guarantees of Encrypted DNS
Get PDFDNS over TLS (DoT) and DNS over HTTPS (DoH) encrypt DNS to guard user privacy by hiding DNS resolutions from passive adversaries. Yet, past attacks have shown that encrypted DNS is still sensitive to traffic analysis. As a consequence, RFC 8467 proposes to pad messages prior to encryption, which heavily reduces the characteristics of encrypted traffic. In this paper, we show that padding alone is insufficient to counter DNS traffic analysis. We propose a novel traffic analysis method that combines size and timing information to infer the websites a user visits purely based on encrypted and padded DNS traces. To this end, we model DNS Sequences that capture the complexity of websites that usually trigger dozens of DNS resolutions instead of just a single DNS transaction. A closed world evaluation based on the Tranco top-10k websites reveals that attackers can deanonymize test traces for 86.1 % of all websites, and even correctly label all traces for 65.9 % of the websites. Our findings undermine the privacy goals of state-of-the-art message padding strategies in DoT/DoH. We conclude by showing that successful mitigations to such attacks have to remove the entropy of inter-arrival timings between query responses