4 ms·

That is only true if you have no interest in recovery post compromise. A user level account shouldn't be able to put the system in such a state that online rec

by woodman 11y ago

That is only true if you have no interest in recovery post compromise. A user level account shouldn't be able to put the system in such a state that online recovery is impossible, whereas a system level account easily can - think loadable kernel modules. Only offline recovery works once you lose trust in the kernel. That is the difference between "Alright grandma, lemme remote in" and "Sorry old lady, better start looking for the factory install CDs". Lets not even get into how screwed we are with UEFI...

kentonv 11y ago
If you have to wipe the user account anyway, then wiping the system at the same time hardly adds any more effort -- in fact it's probably easier. Your system files are the easiest part of your system to recover, because the originals are readily accessible from the vendor.
- woodman 11y ago
  I guess it depends. In the grandma scenario it adds a lot more effort. A corporate laptop in a standard AD environment, no problem. In a situation where you've customized the system (custom packages, sshd.conf tuning, flags in rc/csh/sysctl/resolv/loader/randomsbinutilityinstalled2yearsago.conf) it would be a lot more work than just reinstalling the OS. Use backups you say? What if I told you that you could use the very same backups to rollback changes to the user's home directory, in 5 minutes, and not have to reimage the entire machine? I'm just saying: even on a single user setup - there is a world of difference in what options you have open to you, depending upon whether you let the malware hit ring 0 or not.
  - theinternetman 11y ago
    Not sure why anyone with a compromised machine would rather have the risk of a lingering backdoor just to save 1-2 hours clean formatting and reinstalling
    - bartvk 11y ago
      Me neither, but there's a whole industry of software for Windows users that promises to remove malware.
    - woodman 11y ago
      Because unless an unknown method of privilege elevation was used, it doesn't make sense. Do you throw a pinch of table salt over your shoulder as well? It also has a very strong Microsoft smell to it, where instead of doing root cause analysis on why Windows is misbehaving - you just reboot and cross your fingers.
      - kentonv 11y ago
        > Because unless an unknown method of privilege elevation was used You seem to think that is unlikely. Why? New privesc bugs are found on a monthly basis in Linux and Windows. Does Grandma stay on top of kernel patches? Nobody who does sandbox security (hint: I do sandbox security) thinks UID separation is sufficient to cordon malware anymore.
        woodman 11y ago
        > You seem to think that is unlikely. Why? Because of the single user pc context. I've never seen a dropper that didn't have ring 0 later pull down a payload that escalated privilege. I'm not saying that it isn't possible, but at best it is very uncommon. I understand the better safe than sorry position, but with the context in mind, what safety are you getting by just assuming UID separation failed and going through the rigmarole of reinstallation? The user data has already been exposed. I just don't agree with the simplified decision tree of "Infected --> reinstall", which disregards your work in sandboxing. Why should I even bother with the additional complexity of capability mode in my software, if we're all just assuming our defense has no depth.
        kentonv 11y ago
        > I've never seen a dropper that didn't have ring 0 later pull down a payload that escalated privilege. Probably because it isn't very useful to the attacker. Pwning the single user's account is sufficient. But I wouldn't bet on that being the case if it happened to me. > what safety are you getting by just assuming UID separation failed and going through the rigmarole of reinstallation? The user data has already been exposed. Most user data is not executable, so can probably safely be copied over. But if you don't wipe all executable software on the system it's hard to tell if some of it is still infected. > Why should I even bother with the additional complexity of capability mode in my software, if we're all just assuming our defense has no depth. Well, I'm talking about today's legacy desktop (and, to some extent, server) OSs, which have not prioritized user isolation because it hasn't really mattered ever since people stopped using timeshare systems. Modern OSs that sandbox applications (e.g. ChromeOS, Android, iOS) are another story. I would expect that one Android app being malicious does not mean you have to wipe your phone, just uninstall the app. I would expect that ChromeOS can even recover from a full sandbox breakout, given secure boot. But I don't trust Linux, Windows, or Mac OS desktops to be suitably hardened nor able to recover. And as wiping the whole system does not add very much cost over the cost of wiping the user account, it seems to me worth it to go all the way.

by woodman 11y ago

kentonv 11y ago

If you have to wipe the user account anyway, then wiping the system at the same time hardly adds any more effort -- in fact it's probably easier. Your system files are the easiest part of your system to recover, because the originals are readily accessible from the vendor.

woodman 11y ago
I guess it depends. In the grandma scenario it adds a lot more effort. A corporate laptop in a standard AD environment, no problem. In a situation where you've customized the system (custom packages, sshd.conf tuning, flags in rc/csh/sysctl/resolv/loader/randomsbinutilityinstalled2yearsago.conf) it would be a lot more work than just reinstalling the OS. Use backups you say? What if I told you that you could use the very same backups to rollback changes to the user's home directory, in 5 minutes, and not have to reimage the entire machine? I'm just saying: even on a single user setup - there is a world of difference in what options you have open to you, depending upon whether you let the malware hit ring 0 or not.
- theinternetman 11y ago
  Not sure why anyone with a compromised machine would rather have the risk of a lingering backdoor just to save 1-2 hours clean formatting and reinstalling
  - bartvk 11y ago
    Me neither, but there's a whole industry of software for Windows users that promises to remove malware.
  - woodman 11y ago
    Because unless an unknown method of privilege elevation was used, it doesn't make sense. Do you throw a pinch of table salt over your shoulder as well? It also has a very strong Microsoft smell to it, where instead of doing root cause analysis on why Windows is misbehaving - you just reboot and cross your fingers.
    - kentonv 11y ago
      > Because unless an unknown method of privilege elevation was used You seem to think that is unlikely. Why? New privesc bugs are found on a monthly basis in Linux and Windows. Does Grandma stay on top of kernel patches? Nobody who does sandbox security (hint: I do sandbox security) thinks UID separation is sufficient to cordon malware anymore.
      - woodman 11y ago
        > You seem to think that is unlikely. Why? Because of the single user pc context. I've never seen a dropper that didn't have ring 0 later pull down a payload that escalated privilege. I'm not saying that it isn't possible, but at best it is very uncommon. I understand the better safe than sorry position, but with the context in mind, what safety are you getting by just assuming UID separation failed and going through the rigmarole of reinstallation? The user data has already been exposed. I just don't agree with the simplified decision tree of "Infected --> reinstall", which disregards your work in sandboxing. Why should I even bother with the additional complexity of capability mode in my software, if we're all just assuming our defense has no depth.
        kentonv 11y ago
        > I've never seen a dropper that didn't have ring 0 later pull down a payload that escalated privilege. Probably because it isn't very useful to the attacker. Pwning the single user's account is sufficient. But I wouldn't bet on that being the case if it happened to me. > what safety are you getting by just assuming UID separation failed and going through the rigmarole of reinstallation? The user data has already been exposed. Most user data is not executable, so can probably safely be copied over. But if you don't wipe all executable software on the system it's hard to tell if some of it is still infected. > Why should I even bother with the additional complexity of capability mode in my software, if we're all just assuming our defense has no depth. Well, I'm talking about today's legacy desktop (and, to some extent, server) OSs, which have not prioritized user isolation because it hasn't really mattered ever since people stopped using timeshare systems. Modern OSs that sandbox applications (e.g. ChromeOS, Android, iOS) are another story. I would expect that one Android app being malicious does not mean you have to wipe your phone, just uninstall the app. I would expect that ChromeOS can even recover from a full sandbox breakout, given secure boot. But I don't trust Linux, Windows, or Mac OS desktops to be suitably hardened nor able to recover. And as wiping the whole system does not add very much cost over the cost of wiping the user account, it seems to me worth it to go all the way.