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[MEDIUM] Prevent shell injection through environment interpolation #583

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[MEDIUM] Prevent shell injection through environment interpolation #583

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11 changes: 10 additions & 1 deletion lib/sshkit/command.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,9 @@ module SSHKit
class Command

Failed = Class.new(SSHKit::StandardError)
ENVIRONMENT_VARIABLE = /\A[A-Za-z_][A-Za-z0-9_]*\z/
# Preserve documented $VAR/${VAR} expansion while escaping executable shell forms.
ENVIRONMENT_VALUE_ESCAPE = /\\[$\x60"\\]|["\x60]|\$(?![A-Za-z_][A-Za-z0-9_]*|\{[A-Za-z_][A-Za-z0-9_]*\})/

attr_reader :command, :args, :options, :started_at, :started, :exit_status, :full_stdout, :full_stderr, :uuid

Expand Down Expand Up @@ -153,7 +156,13 @@ def environment_hash
def environment_string
environment_hash.collect do |key,value|
key_string = key.is_a?(Symbol) ? key.to_s.upcase : key.to_s
escaped_value = value.to_s.gsub(/"/, '\"')
unless key_string.match?(ENVIRONMENT_VARIABLE)
raise ArgumentError, "Invalid environment variable name: #{key.inspect}"
end

escaped_value = value.to_s.gsub(ENVIRONMENT_VALUE_ESCAPE) do |match|
match.start_with?("\\") ? match : "\\#{match}"
end
%{#{key_string}="#{escaped_value}"}
end.join(' ')
end
Expand Down