Rashomon of disclosure
> In a world of changing technology, there are few constants - but if there is one constant in security, it is the rhythmic flare-up of discussions about disclosure on the social-media-du-jour (mailing lists in the past, now mostly Twitter and Facebook).
> In this blog post, I would like to highlight a few aspects of the discussion that are important to me personally - aspects which influenced my thinking, and which are underappreciated in my view.
The Matasano Crypto Challenges (review)
If you don’t have time for the challenges themselves, reading this review a few times until the lessons are internalized may be a good substitute.
> How practical these attacks were. A lot of stuff that I knew was weak in principle (like re-using a nonce or using a timestamp as a ‘random’ seed) turns out to be crackable within seconds by an art major writing crappy Python.
> We present an attack on the encryption key negotiation protocol of Bluetooth BR/EDR. The attack allows a third party, without knowledge of any secret material (such as link and encryption keys), to make two (or more) victims agree on an encryption key with only 1 byte (8 bits) of entropy. Such low entropy enables the attacker to easily brute force the negotiated encryption keys, decrypt the eavesdropped ciphertext, and inject valid encrypted messages (in real-time). The attack is stealthy because the encryption key negotiation is transparent to the Bluetooth users. The attack is standard-compliant because all Bluetooth BR/EDR versions require to support encryption keys with entropy between 1 and 16 bytes and do not secure the key negotiation protocol. As a result, the attacker completely breaks Bluetooth BR/EDR security without being detected. We call our attack Key Negotiation Of Bluetooth (KNOB) attack.
HTTP/2 Denial of Service Advisory
> Netflix has discovered several resource exhaustion vectors affecting a variety of third-party HTTP/2 implementations. These attack vectors can be used to launch DoS attacks against servers that support HTTP/2 communication.
Son of Slowloris returns!
> While this added complexity enables some exciting new features, it also raises implementation questions.
Here comes trouble...
> The Security Considerations section of RFC 7540 (see Section 10.5) addresses some of this in a general way. However, unlike the expected “normal” behavior—which is well-documented and which implementations seem to follow very closely—the algorithms and mechanisms for detecting and mitigating “abnormal” behavior are significantly more vague and left as an exercise for the implementer. From a review of various software packages, it appears that this has led to a variety of implementations with a variety of good ideas, but also some weaknesses.
Down the Rabbit-Hole...
> I often find it valuable to write simple test cases confirming things work the way I think they do. Sometimes I can’t explain the results, and getting to the bottom of those discrepancies can reveal new research opportunities. This is the story of one of those discrepancies; and the security rabbit-hole it led me down.
> Any application, any user - even sandboxed processes - can connect to any CTF session. Clients are expected to report their thread id, process id and HWND, but there is no authentication involved and you can simply lie. Secondly, there is nothing stopping you pretending to be a CTF service and getting other applications - even privileged applications - to connect to you.
> Even without bugs, the CTF protocol allows applications to exchange input and read each other’s content. However, there are a lot of protocol bugs that allow taking complete control of almost any other application.
Regarding disclosure: https://bugs.chromium.org/p/project-zero/issues/detail?id=1859#c10
Bzip2 And The Cve That Wasn’t
> Compiling with the GCC sanitizers and then fuzzing the resulting binaries might find real bugs. But not all such bugs are security issues. When a CVE is filed there is some pressure to treat such an issue with urgency and push out a fix as soon as possible. But taking your time and making sure an issue can be replicated/exploited without the binary being instrumented by the sanitizer is often better.
I don’t think anything went wrong here, but some interesting details.
The Exxon Valdez of cyberspace
> In 1989 the thin-hulled Exxon Valdez supertanker ran aground in Prince William Sound, Alaska, pouring a quarter of a million barrels of oil into the surrounding waters. At the time, it was America’s worst offshore spill, and a huge blow to the reputation of the ship’s owner, Exxon. The firm paid $3bn to clean up the area and settle legal claims, and to improve safety the American government ordered the phasing out of single-hull ships such as Exxon Valdez. All vessels used worldwide by Exxon’s corporate descendant, ExxonMobil, are now double-hulled. But that is not all. The disaster gave rise to a cultlike culture of discipline within ExxonMobil that helped turn it into the profitmaking beast it is today.
If we haven’t yet seen a sufficiently nasty data breach to motivate cleanups, I don’t think we want to.
Spying on HTTPS
> While most users probably would have no idea what to make of this, I happened to know what it means– Chrome is warning me that the system configuration has instructed it to leak the secret keys it uses to encrypt and decrypt HTTPS traffic to a stream on the local computer.
Username (and password) free login with security keys
> Most readers of this blog will be familiar with the traditional security key user experience: you register a token with a site then, when logging in, you enter a username and password as normal but are also required to press a security key in order for it to sign a challenge from the website. This is an effective defense against phishing, phone number takeover, etc. But modern security keys are capable of serving the roles of username and password too, so the user experience can just involve clicking a login button, pressing the security key, and (perhaps) entering a locally-validated PIN if the security key doesn’t do biometrics. This is possible with the recently released Chromium 76 and also with Edge or Firefox on current versions of Windows.
> That begs the question: what’s the difference between a PIN and a password? On the surface: nothing. A security key PIN is an arbitrary string, not limited to numbers. (I think it was probably considered too embarrassing to call it a password since FIDO’s slogan is “solving the world’s password problem”.)
One core problem with DNSSEC
> One fundamental problem of DNSSEC today is that it suffers from the false positive problem, the same one that security alerts suffer from. In practice today, for almost all people almost all of the time, a DNSSEC failure is not a genuine attack; it is a configuration mistake, and the configuration mistake is almost never on the side making the DNS query. This means that almost all of the time, DNSSEC acts by stopping you from doing something safe that you want to do and further, you can’t fix the DNSSEC problem except by turning off DNSSEC, because it’s someone else’s mistake (in configuration, in operation, or in whatever).
APRR - Access Protection ReRouting
> Almost a year ago I did a write-up on KTRR, first introduced in Apple’s A10 chip series. Now over the course of the last year, there has been a good bit of talk as well as confusion about the new mitigations shipped with Apple’s A12. One big change, PAC, has already been torn down in detail by Brandon Azad, so I’m gonna leave that out here. What’s left to cover is more than just APRR, but APRR is certainly the biggest chunk, hence the title of this post.
> APRR is a pretty cool feature, even if parts of it are kinda broke. What I really like about it (besides the fact that it is an efficient and elegant solution to switching privileges) is that it untangles EL1 and EL0 memory permissions, giving you more flexibility than a standard ARMv8 implementation. What I don’t like though is that it has clearly been designed as a lockdown feature, allowing you only to take permissions away rather than freely remap them.
> It’s also evident that Apple is really fond of post-exploit mitigations, or just mitigations in general. And on one hand, getting control over the physical address space is a good bit harder now. But on the other hand, Apple’s stacking of mitigations is taking a problematic turn when adding new mitigations actively creates vulnerabilities now.
HTTP Desync Attacks: Request Smuggling Reborn
> HTTP requests are traditionally viewed as isolated, standalone entities. In this paper, I’ll explore forgotten techniques for remote, unauthenticated attackers to smash through this isolation and splice their requests into others, through which I was able to play puppeteer with the web infrastructure of numerous commercial and military systems, rain exploits on their visitors, and harvest over $70k in bug bounties.
> The protocol is extremely simple - HTTP requests are simply placed back to back, and the server parses headers to work out where each one ends and the next one starts. This is often confused with HTTP pipelining, which is a rarer subtype that’s not required for the attacks described in this paper. By itself, this is harmless. However, modern websites are composed of chains of systems, all talking over HTTP. This multi-tiered architecture takes HTTP requests from multiple different users and routes them over a single TCP/TLS connection:
The Fully Remote Attack Surface of the iPhone
> We investigated the remote attack surface of the iPhone, and reviewed SMS, MMS, VVM, Email and iMessage. Several tools which can be used to further test these attack surfaces were released. We reported a total of 10 vulnerabilities, all of which have since been fixed. The majority of vulnerabilities occurred in iMessage due to its broad and difficult to enumerate attack surface. Most of this attack surface is not part of normal use, and does not have any benefit to users. Visual Voicemail also had a large and unintuitive attack surface that likely led to a single serious vulnerability being reported in it. Overall, the number and severity of the remote vulnerabilities we found was substantial. Reducing the remote attack surface of the iPhone would likely improve its security.
Better Encrypted Group Chat
> End-to-end encrypted group messaging is also a hard problem to solve. Existing solutions such as Signal, WhatsApp, and iMessage have inherent problems with scaling, which I’ll discuss in detail, that make it infeasible to conduct group chats of more than a few hundred people. The Message Layer Security (MLS) protocol aims to make end-to-end encrypted group chat more efficient while still providing security guarantees like forward secrecy and post-compromise security.
> The primary contribution of molasses has been in detecting errors in the specification and other implementations through unit and interoperability testing. Molasses implements most of MLS draft 6. Why not all of draft 6? There was an error in the spec that made it impossible for members to be added to any group. This broke all the unit tests that create non-trivial groups. Errors like this are hard to catch just by reading the spec; they require some amount of automated digging. Once they are found, the necessary revisions tend to be pretty obvious, and they are swiftly incorporated into the subsequent draft.
Nice work and a very nice explanation of the protocol.
clamav: denial of service through "better zip bomb"
> Recently David Fifield presented a new variant of a ZIP bomb where by using overlapping segments he was able to achieve very high compression ratios (42kb->5GB, 10MB->281TB).
> However David Fifield commented in the bug report  that the fix is incomplete, by using some slight variations of his methods he could bypass the fix.
This shouldn’t be anything new, but... oops. Plus some commentary about age browsing, etc.
Dragonblood new results
> August 2019 — During our initial disclosure, the Wi-Fi Alliance privately created security recommendations to mitigate our attacks. In these recommendations, they claim that Brainpool curves are safe to use, at least if products securely implement Dragonfly’s quadratic residue test (i.e. it must be implemented without side-channel leaks). However, we found that using Brainpool curves introduces a second class of side-channel leaks in the Dragonfly handshake of WPA3. In other words, even if the advice of the Wi-Fi Alliance is followed, implementations remain at risk of attacks. This demonstrates that implementing Dragonfly and WPA3 without side-channel leaks is surprisingly hard. It also, once again, shows that privately creating security recommendations and standards is at best irresponsible and at worst inept.
That last line.
Adopting the Arm Memory Tagging Extension in Android
> As part of our continuous commitment to improve the security of the Android ecosystem, we are partnering with Arm to design the memory tagging extension (MTE). Memory safety bugs, common in C and C++, remain one of the largest vulnerabilities in the Android platform and although there have been previous hardening efforts, memory safety bugs comprised more than half of the high priority security bugs in Android 9.
> We believe that memory tagging will detect the most common classes of memory safety bugs in the wild, helping vendors identify and fix them, discouraging malicious actors from exploiting them. During the past year, our team has been working to ensure readiness of the Android platform and application software for MTE. We have deployed HWASAN, a software implementation of the memory tagging concept, to test our entire platform and a few select apps. This deployment has uncovered close to 100 memory safety bugs. The majority of these bugs were detected on HWASAN enabled phones in everyday use. MTE will greatly improve upon this in terms of overhead, ease of deployment, and scale. In parallel, we have been working on supporting MTE in the LLVM compiler toolchain and in the Linux kernel. The Android platform support for MTE will be complete by the time of silicon availability.
vDSO, 32-bit time, and seccomp
> The seccomp() mechanism is notoriously difficult to use. It also turns out to be easy to break unintentionally, as the development community discovered when a timekeeping change meant to address the year-2038 problem created a regression for seccomp() users in the 5.3 kernel. Work is underway to mitigate the problem for now, but seccomp() users on 32-bit systems are likely to have to change their configurations at some point.
The problems inherent in exposing very low level interfaces in one place (seccomp) and high level interfaces in another (libc).
2019 Pwnies Award Nominations
Shit happened. Mistakes were made.
Preventing The Capital One Breach
> Every indication is that the attacker exploited a type of vulnerability known as Server Side Request Forgery (SSRF) in order to perform the attack. SSRF has become the most serious vulnerability facing organizations that use public clouds. SSRF is not an unknown vulnerability, but it doesn’t receive enough attention and was absent from the OWASP Top 10.
> SSRF is a bug hunters dream because it is an easy to perform attack and regularly yields critical findings, like this bug bounty report to Shopify. The problem is common and well-known, but hard to prevent and does not have any mitigations built in to the AWS platform.