[ANN] RubyGems 0.9.0 and earlier installation exploit

[Eric Hodel]

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Problem Description:

RubyGems does not check installation paths for gems before writing
files.

Impact:

Since RubyGems packages are typically installed using root
permissions, arbitrary files may be overwritten on-disk. This may
lead to denial of service, privilege escalation or remote compromise.

Workaround:

No known workarounds

Solution:

a) Upgrade to RubyGems 0.9.1

b) Apply one of the following patches

For RubyGems 0.9.0:


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Index: lib/rubygems/installer.rb
===================================================================
--- lib/rubygems/installer.rb (revision 1195)
+++ lib/rubygems/installer.rb (working copy)
@@ -335,14 +335,20 @@ TEXT
#
def extract_files(directory, format)
require 'fileutils'
- wd = Dir.getwd
- Dir.chdir directory do
- format.file_entries.each do |entry, file_data|
- path = entry['path'].untaint
- FileUtils.mkdir_p File.dirname(path)
- File.open(path, "wb") do |out|
- out.write file_data
- end
+ format.file_entries.each do |entry, file_data|
+ path = entry['path'].untaint
+ if path =~ /\A\// then # for extra sanity
+ raise Gem::InstallError,
+ "attempt to install file into #{entry['path'].inspect}"
+ end
+ path = File.expand_path File.join(directory, path)
+ if path !~ /\A#{Regexp.escape directory}/ then
+ raise Gem::InstallError,
+ "attempt to install file into #{entry['path'].inspect}"
+ end
+ FileUtils.mkdir_p File.dirname(path)
+ File.open(path, "wb") do |out|
+ out.write file_data
end
end
end

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For RubyGems 0.8.11:


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Index: lib/rubygems/installer.rb
===================================================================
--- lib/rubygems/installer.rb (revision 1195)
+++ lib/rubygems/installer.rb (working copy)
@@ -7,6 +7,8 @@ require 'rubygems/dependency_list'

module Gem

+ class InstallError < Gem::Exception; end
+
class DependencyRemovalException < Gem::Exception; end

##
@@ -321,14 +323,20 @@ TEXT
#
def extract_files(directory, format)
require 'fileutils'
- wd = Dir.getwd
- Dir.chdir directory do
- format.file_entries.each do |entry, file_data|
- path = entry['path']
- FileUtils.mkdir_p File.dirname(path)
- File.open(path, "wb") do |out|
- out.write file_data
- end
+ format.file_entries.each do |entry, file_data|
+ path = entry['path']
+ if path =~ /\A\// then # for extra sanity
+ raise Gem::InstallError,
+ "attempt to install file into #{entry['path'].inspect}"
+ end
+ path = File.expand_path File.join(directory, path)
+ if path !~ /\A#{Regexp.escape directory}/ then
+ raise Gem::InstallError,
+ "attempt to install file into #{entry['path'].inspect}"
+ end
+ FileUtils.mkdir_p File.dirname(path)
+ File.open(path, "wb") do |out|
+ out.write file_data
end
end
end

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Note:

Remote installations via Rubyforge will be disabled in the near
future for versions of RubyGems earlier than 0.9.1, even for patched
versions of RubyGems. Local installations will continue to work,
however.

Thanks to Gavin Sinclair for finding and reporting this problem.

Testing your updated RubyGems:

Installing rspec-0.7.5 will give an InstallError on a patched version
of RubyGems:

$ gem install rspec --version 0.7.5
ERROR: While executing gem ... (Gem::InstallError)
attempt to install file into "../web_spec/
web_test_html_formatter.rb"

The rspec teams reports that an updated rspec will be released later
today or tomorrow.

--
Eric Hodel - (e-mail address removed) - http://blog.segment7.net

I LIT YOUR GEM ON FIRE!



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