Hi all,
There have been a series of recent attacks that take advantage of "rowhammer" (a RAM hardware bit-flipping vulnerability) to flip bits in security-critical data structures.
VMs sharing the same physical RAM are vulnerable, and browsers and mobile apps are remote vectors with proof-of-concept implementations.
Rowhammer summary: https://en.wikipedia.org/wiki/Row_hammer
An attack that flips targeted bits in another virtual machine on the same physical RAM, targeting OpenSSH public keys, GPG public keys, and Debian package sources: https://www.vusec.net/projects/flip-feng-shui/
A similar proof-of-concept Android app: https://www.vusec.net/projects/drammer/
A JavaScript-based in-browser remote proof-of-concept: https://arxiv.org/pdf/1507.06955v1.pdf
It seems like a short step from these existing attacks to targeting Tor Browser users remotely. I wonder whether it might be possible to target relays (or clients) using OR cells or directory documents with specific content, but this seems much less likely.
I have been thinking about how we could make Tor (and browsers, and other processes, and OSs) less vulnerable to these kinds of attacks.
In general, some of the process-level defences against one or more of the above attacks are: * sign or checksum all security-critical data structures, * implement and check cross-certification, * don't rely on cached checks (or checks performed at load time) continuing to be accurate, * minimise time between checking validity and using the data, (this includes signatures, checksums, data structure consistency) * make the content of memory pages (including loaded files) less predictable, * make sure the hamming distance between trusted, valid inputs and untrusted, valid inputs is large, in particular: * register domains that are one bit-flip away from trusted domains, (or, alternately, mandate SSL, and pin certificates, and fix broken CA roots)
Some of the OS-level defences are: * turn off memory deduplication, * write and verify checksums on each page,
Some of the firmware/hardware defences are: * increase the RAM refresh rate, * improve RAM design, * use ECC RAM.
T
On 2016-11-18 00:03, teor wrote:
Hi all,
There have been a series of recent attacks that take advantage of "rowhammer" (a RAM hardware bit-flipping vulnerability) to flip bits in security-critical data structures.
VMs sharing the same physical RAM are vulnerable, and browsers and mobile apps are remote vectors with proof-of-concept implementations.
Rowhammer summary: https://en.wikipedia.org/wiki/Row_hammer
An attack that flips targeted bits in another virtual machine on the same physical RAM, targeting OpenSSH public keys, GPG public keys, and Debian package sources: https://www.vusec.net/projects/flip-feng-shui/
A similar proof-of-concept Android app: https://www.vusec.net/projects/drammer/
A JavaScript-based in-browser remote proof-of-concept: https://arxiv.org/pdf/1507.06955v1.pdf
It seems like a short step from these existing attacks to targeting Tor Browser users remotely. I wonder whether it might be possible to target relays (or clients) using OR cells or directory documents with specific content, but this seems much less likely.
I have been thinking about how we could make Tor (and browsers, and other processes, and OSs) less vulnerable to these kinds of attacks.
In general, some of the process-level defences against one or more of the above attacks are:
- sign or checksum all security-critical data structures,
- implement and check cross-certification,
- don't rely on cached checks (or checks performed at load time) continuing to be accurate,
- minimise time between checking validity and using the data, (this includes signatures, checksums, data structure consistency)
- make the content of memory pages (including loaded files) less predictable,
- make sure the hamming distance between trusted, valid inputs and untrusted, valid inputs is large, in particular:
(or, alternately, mandate SSL, and pin certificates, and fix broken CA roots)
- register domains that are one bit-flip away from trusted domains,
Some of the OS-level defences are:
- turn off memory deduplication,
- write and verify checksums on each page,
Some of the firmware/hardware defences are:
- increase the RAM refresh rate,
- improve RAM design,
- use ECC RAM.
T
We've been keeping track of these attack classes on hypervisors:
https://www.whonix.org/wiki/Advanced_Attacks https://www.whonix.org/wiki/KVM#Unsafe_Features
Its great to design software that's resistant to adversarial conditions anyhow.
-
bancfcï¼ openmailbox.org -
teor