mastodon/app/controllers/concerns/signature_verification.rb
Eugen Rochko fac529975b Improve signature verification safeguards (#8959)
* Downcase signed_headers string before building the signed string

The HTTP Signatures draft does not mandate the “headers” field to be downcased,
but mandates the header field names to be downcased in the signed string, which
means that prior to this patch, Mastodon could fail to process signatures from
some compliant clients. It also means that it would not actually check the
Digest of non-compliant clients that wouldn't use a lowercased Digest field
name.

Thankfully, I don't know of any such client.

* Revert "Remove dead code (#8919)"

This reverts commit a00ce8c92c.

* Restore time window checking, change it to 12 hours

By checking the Date header, we can prevent replaying old vulnerable
signatures. The focus is to prevent replaying old vulnerable requests
from software that has been fixed in the meantime, so a somewhat long
window should be fine and accounts for timezone misconfiguration.

* Escape users' URLs when formatting them

Fixes possible HTML injection

* Escape all string interpolations in Formatter class

Slightly improve performance by reducing class allocations
from repeated Formatter#encode calls

* Fix code style issues
2018-10-12 07:00:41 +02:00

129 lines
4 KiB
Ruby

# frozen_string_literal: true
# Implemented according to HTTP signatures (Draft 6)
# <https://tools.ietf.org/html/draft-cavage-http-signatures-06>
module SignatureVerification
extend ActiveSupport::Concern
def signed_request?
request.headers['Signature'].present?
end
def signature_verification_failure_reason
return @signature_verification_failure_reason if defined?(@signature_verification_failure_reason)
end
def signed_request_account
return @signed_request_account if defined?(@signed_request_account)
unless signed_request?
@signature_verification_failure_reason = 'Request not signed'
@signed_request_account = nil
return
end
if request.headers['Date'].present? && !matches_time_window?
@signature_verification_failure_reason = 'Signed request date outside acceptable time window'
@signed_request_account = nil
return
end
raw_signature = request.headers['Signature']
signature_params = {}
raw_signature.split(',').each do |part|
parsed_parts = part.match(/([a-z]+)="([^"]+)"/i)
next if parsed_parts.nil? || parsed_parts.size != 3
signature_params[parsed_parts[1]] = parsed_parts[2]
end
if incompatible_signature?(signature_params)
@signature_verification_failure_reason = 'Incompatible request signature'
@signed_request_account = nil
return
end
account = account_from_key_id(signature_params['keyId'])
if account.nil?
@signature_verification_failure_reason = "Public key not found for key #{signature_params['keyId']}"
@signed_request_account = nil
return
end
signature = Base64.decode64(signature_params['signature'])
compare_signed_string = build_signed_string(signature_params['headers'])
if account.keypair.public_key.verify(OpenSSL::Digest::SHA256.new, signature, compare_signed_string)
@signed_request_account = account
@signed_request_account
elsif account.possibly_stale?
account = account.refresh!
if account.keypair.public_key.verify(OpenSSL::Digest::SHA256.new, signature, compare_signed_string)
@signed_request_account = account
@signed_request_account
else
@signature_verification_failure_reason = "Verification failed for #{account.username}@#{account.domain} #{account.uri}"
@signed_request_account = nil
end
else
@signature_verification_failure_reason = "Verification failed for #{account.username}@#{account.domain} #{account.uri}"
@signed_request_account = nil
end
end
def request_body
@request_body ||= request.raw_post
end
private
def build_signed_string(signed_headers)
signed_headers = 'date' if signed_headers.blank?
signed_headers.downcase.split(' ').map do |signed_header|
if signed_header == Request::REQUEST_TARGET
"#{Request::REQUEST_TARGET}: #{request.method.downcase} #{request.path}"
elsif signed_header == 'digest'
"digest: #{body_digest}"
else
"#{signed_header}: #{request.headers[to_header_name(signed_header)]}"
end
end.join("\n")
end
def matches_time_window?
begin
time_sent = Time.httpdate(request.headers['Date'])
rescue ArgumentError
return false
end
(Time.now.utc - time_sent).abs <= 12.hours
end
def body_digest
"SHA-256=#{Digest::SHA256.base64digest(request_body)}"
end
def to_header_name(name)
name.split(/-/).map(&:capitalize).join('-')
end
def incompatible_signature?(signature_params)
signature_params['keyId'].blank? ||
signature_params['signature'].blank?
end
def account_from_key_id(key_id)
if key_id.start_with?('acct:')
ResolveAccountService.new.call(key_id.gsub(/\Aacct:/, ''))
elsif !ActivityPub::TagManager.instance.local_uri?(key_id)
account = ActivityPub::TagManager.instance.uri_to_resource(key_id, Account)
account ||= ActivityPub::FetchRemoteKeyService.new.call(key_id, id: false)
account
end
end
end