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Another Bloomberg Story about Supply-Chain Hardware Attacks from China

Bloomberg has another story about hardware surveillance implants in equipment made in China. This implant is different from the one Bloomberg reported on last week. That story has been denied by pretty much everyone else, but Bloomberg is sticking by its story and its sources. (I linked to other commentary and analysis here.)

Again, I have no idea what’s true. The story is plausible. The denials are about what you’d expect. My lone hesitation to believing this is not seeing a photo of the hardware implant. If these things were in servers all over the US, you’d think someone would have come up with a photograph by now.

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New Variants of Cold-Boot Attack

If someone has physical access to your locked — but still running — computer, they can probably break the hard drive’s encryption. This is a “cold boot” attack, and one we thought solved. We have not:

To carry out the attack, the F-Secure researchers first sought a way to defeat the the industry-standard cold boot mitigation. The protection works by creating a simple check between an operating system and a computer’s firmware, the fundamental code that coordinates hardware and software for things like initiating booting. The operating system sets a sort of flag or marker indicating that it has secret data stored in its memory, and when the computer boots up, its firmware checks for the flag. If the computer shuts down normally, the operating system wipes the data and the flag with it. But if the firmware detects the flag during the boot process, it takes over the responsibility of wiping the memory before anything else can happen.

Looking at this arrangement, the researchers realized a problem. If they physically opened a computer and directly connected to the chip that runs the firmware and the flag, they could interact with it and clear the flag. This would make the computer think it shut down correctly and that the operating system wiped the memory, because the flag was gone, when actually potentially sensitive data was still there.

So the researchers designed a relatively simple microcontroller and program that can connect to the chip the firmware is on and manipulate the flag. From there, an attacker could move ahead with a standard cold boot attack. Though any number of things could be stored in memory when a computer is idle, Segerdahl notes that an attacker can be sure the device’s decryption keys will be among them if she is staring down a computer’s login screen, which is waiting to check any inputs against the correct ones.

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Speculation Attack Against Intel’s SGX

Another speculative-execution attack against Intel’s SGX.

At a high level, SGX is a new feature in modern Intel CPUs which allows computers to protect users’ data even if the entire system falls under the attacker’s control. While it was previously believed that SGX is resilient to speculative execution attacks (such as Meltdown and Spectre), Foreshadow demonstrates how speculative execution can be exploited for reading the contents of SGX-protected memory as well as extracting the machine’s private attestation key. Making things worse, due to SGX’s privacy features, an attestation report cannot be linked to the identity of its signer. Thus, it only takes a single compromised SGX machine to erode trust in the entire SGX ecosystem.

News article.

The details of the Foreshadow attack are a little more complicated than those of Meltdown. In Meltdown, the attempt to perform an illegal read of kernel memory triggers the page fault mechanism (by which the processor and operating system cooperate to determine which bit of physical memory a memory access corresponds to, or they crash the program if there’s no such mapping). Attempts to read SGX data from outside an enclave receive special handling by the processor: reads always return a specific value (-1), and writes are ignored completely. The special handling is called “abort page semantics” and should be enough to prevent speculative reads from being able to learn anything.

However, the Foreshadow researchers found a way to bypass the abort page semantics. The data structures used to control the mapping of virtual-memory addresses to physical addresses include a flag to say whether a piece of memory is present (loaded into RAM somewhere) or not. If memory is marked as not being present at all, the processor stops performing any further permissions checks and immediately triggers the page fault mechanism: this means that the abort page mechanics aren’t used. It turns out that applications can mark memory, including enclave memory, as not being present by removing all permissions (read, write, execute) from that memory.

EDITED TO ADD: Intel has responded:

L1 Terminal Fault is addressed by microcode updates released earlier this year, coupled with corresponding updates to operating system and hypervisor software that are available starting today. We’ve provided more information on our web site and continue to encourage everyone to keep their systems up-to-date, as it’s one of the best ways to stay protected.

I think this is a comprehensive link to everything the company is saying about the vulnerability.

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Another Spectre-Like CPU Vulnerability

Google and Microsoft researchers have disclosed another Spectre-like CPU side-channel vulnerability, called “Speculative Store Bypass.” Like the others, the fix will slow the CPU down.

The German tech site Heise reports that more are coming.

I’m not surprised. Writing about Spectre and Meltdown in January, I predicted that we’ll be seeing a lot more of these sorts of vulnerabilities.

Spectre and Meltdown are pretty catastrophic vulnerabilities, but they only affect the confidentiality of data. Now that they — and the research into the Intel ME vulnerability — have shown researchers where to look, more is coming — and what they’ll find will be worse than either Spectre or Meltdown.

I still predict that we’ll be seeing lots more of these in the coming months and years, as we learn more about this class of vulnerabilities.

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Another Branch Prediction Attack

When Spectre and Meltdown were first announced earlier this year, pretty much everyone predicted that there would be many more attacks targeting branch prediction in microprocessors. Here’s another one:

In the new attack, an attacker primes the PHT and running branch instructions so that the PHT will always assume a particular branch is taken or not taken. The victim code then runs and makes a branch, which is potentially disturbing the PHT. The attacker then runs more branch instructions of its own to detect that disturbance to the PHT; the attacker knows that some branches should be predicted in a particular direction and tests to see if the victim’s code has changed that prediction.

The researchers looked only at Intel processors, using the attacks to leak information protected using Intel’s SGX (Software Guard Extensions), a feature found on certain chips to carve out small sections of encrypted code and data such that even the operating system (or virtualization software) cannot access it. They also described ways the attack could be used against address space layout randomization and to infer data in encryption and image libraries.

Research paper.

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Adding Backdoors at the Chip Level

Interesting research into undetectably adding backdoors into computer chips during manufacture: “Stealthy dopant-level hardware Trojans: extended version,” also available here:

Abstract: In recent years, hardware Trojans have drawn the attention of governments and industry as well as the scientific community. One of the main concerns is that integrated circuits, e.g., for military or critical-infrastructure applications, could be maliciously manipulated during the manufacturing process, which often takes place abroad. However, since there have been no reported hardware Trojans in practice yet, little is known about how such a Trojan would look like and how difficult it would be in practice to implement one. In this paper we propose an extremely stealthy approach for implementing hardware Trojans below the gate level, and we evaluate their impact on the security of the target device. Instead of adding additional circuitry to the target design, we insert our hardware Trojans by changing the dopant polarity of existing transistors. Since the modified circuit appears legitimate on all wiring layers (including all metal and polysilicon), our family of Trojans is resistant to most detection techniques, including fine-grain optical inspection and checking against “golden chips”. We demonstrate the effectiveness of our approach by inserting Trojans into two designs — a digital post-processing derived from Intel’s cryptographically secure RNG design used in the Ivy Bridge processors and a side-channel resistant SBox implementation¬≠ — and by exploring their detectability and their effects on security.

The moral is that this kind of technique is very difficult to detect.

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Spectre and Meltdown Attacks

After a week or so of rumors, everyone is now reporting about the Spectre and Meltdown attacks against pretty much every modern processor out there.

These are side-channel attacks where one process can spy on other processes. They affect computers where an untrusted browser window can execute code, phones that have multiple apps running at the same time, and cloud computing networks that run lots of different processes at once. Fixing them either requires a patch that results in a major performance hit, or is impossible and requires a re-architecture of conditional execution in future CPU chips.

I’ll be writing something for publication over the next few days. This post is basically just a link repository.

EDITED TO ADD: Good technical explanation. And a Slashdot thread.

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