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Prevent timing attack on CSRF #123

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Prevent timing attack on CSRF #123

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08ae7cf
use secure compare instead of equal compare to prevent timing attacks
eutopian Nov 13, 2018
c65a015
added test
eutopian Nov 14, 2018
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13 changes: 12 additions & 1 deletion lib/omniauth/strategies/oauth2.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -67,7 +67,7 @@ def callback_phase # rubocop:disable AbcSize, CyclomaticComplexity, MethodLength
error = request.params["error_reason"] || request.params["error"]
if error
fail!(error, CallbackError.new(request.params["error"], request.params["error_description"] || request.params["error_reason"], request.params["error_uri"]))
elsif !options.provider_ignores_state && (request.params["state"].to_s.empty? || request.params["state"] != session.delete("omniauth.state"))
elsif !options.provider_ignores_state && (request.params["state"].to_s.empty? || !secure_compare(request.params["state"], session.delete("omniauth.state")))
fail!(:csrf_detected, CallbackError.new(:csrf_detected, "CSRF detected"))
else
self.access_token = build_access_token
Expand Down Expand Up @@ -105,6 +105,17 @@ def options_for(option)
hash
end

# constant-time comparison algorithm to prevent timing attacks
def secure_compare(string_a, string_b)
return false unless string_a.bytesize == string_b.bytesize

l = string_a.unpack "C#{string_a.bytesize}"

res = 0
string_b.each_byte { |byte| res |= byte ^ l.shift }
res.zero?
end

# An error that is indicated in the OAuth 2.0 callback.
# This could be a `redirect_uri_mismatch` or other
class CallbackError < StandardError
Expand Down
10 changes: 10 additions & 0 deletions spec/omniauth/strategies/oauth2_spec.rb
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Expand Up @@ -87,6 +87,16 @@ def app
instance.callback_phase
end
end

describe "#secure_params" do
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Suggested change
describe "#secure_params" do
describe "#secure_compare" do

subject { fresh_strategy }

it "returns true when the two inputs are the same and false otherwise" do
instance = subject.new("abc", "def")
expect(instance.send(:secure_compare, "a", "a")).to be true
expect(instance.send(:secure_compare, "b", "a")).to be false
end
end
end

describe OmniAuth::Strategies::OAuth2::CallbackError do
Expand Down