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# frozen_string_literal: true
module Gitlab
module Middleware
# There is no valid reason for a request to contain a malformed string
# so just return HTTP 400 (Bad Request) if we receive one
class HandleMalformedStrings
include ActionController::HttpAuthentication::Basic
NULL_BYTE_REGEX = Regexp.new(Regexp.escape("\u0000")).freeze
attr_reader :app
def initialize(app)
@app = app
end
def call(env)
return [400, { 'Content-Type' => 'text/plain' }, ['Bad Request']] if request_contains_malformed_string?(env)
app.call(env)
end
private
def request_contains_malformed_string?(env)
return false if ENV['DISABLE_REQUEST_VALIDATION'] == '1'
# Duplicate the env, so it is not modified when accessing the parameters
# https://github.com/rails/rails/blob/34991a6ae2fc68347c01ea7382fa89004159e019/actionpack/lib/action_dispatch/http/parameters.rb#L59
# The modification causes problems with our multipart middleware
request = ActionDispatch::Request.new(env.dup)
return true if malformed_path?(request.path)
return true if credentials_malformed?(request)
request.params.values.any? do |value|
param_has_null_byte?(value)
end
rescue ActionController::BadRequest, ActionDispatch::Http::Parameters::ParseError
# If we can't build an ActionDispatch::Request something's wrong
# This would also happen if `#params` contains invalid UTF-8
# in this case we'll return a 400
#
true
end
def malformed_path?(path)
string_malformed?(Rack::Utils.unescape(path))
rescue ArgumentError
# Rack::Utils.unescape raised this, path is malformed.
true
end
def credentials_malformed?(request)
credentials = if has_basic_credentials?(request)
decode_credentials(request).presence
else
request.authorization.presence
end
return false unless credentials
string_malformed?(credentials)
end
def param_has_null_byte?(value, depth = 0)
# Guard against possible attack sending large amounts of nested params
# Should be safe as deeply nested params are highly uncommon.
return false if depth > 2
depth += 1
if value.respond_to?(:match)
string_malformed?(value)
elsif value.respond_to?(:values)
value.values.any? do |hash_value|
param_has_null_byte?(hash_value, depth)
end
elsif value.is_a?(Array)
value.any? do |array_value|
param_has_null_byte?(array_value, depth)
end
else
false
end
end
def string_malformed?(string)
# We're using match rather than include, because that will raise an ArgumentError
# when the string contains invalid UTF8
#
# We try to encode the string from ASCII-8BIT to UTF8. If we failed to do
# so for certain characters in the string, those chars are probably incomplete
# multibyte characters.
string.dup.force_encoding(Encoding::UTF_8).match?(NULL_BYTE_REGEX)
rescue ArgumentError, Encoding::UndefinedConversionError
# If we're here, we caught a malformed string. Return true
true
end
end
end
end
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