From 21ad21cb507d7a5f48ef8ee726b2f9308052aa9d Mon Sep 17 00:00:00 2001
From: Eugen Rochko <eugen@zeonfederated.com>
Date: Fri, 12 Oct 2018 00:15:55 +0200
Subject: [PATCH] Improve signature verification safeguards (#8959)
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* 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 a00ce8c92c06f42109aad5cfe65d46862cf037bb.
* 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
---
.../concerns/signature_verification.rb | 18 +++++++++++++-
app/lib/formatter.rb | 16 ++++++++-----
.../concerns/signature_verification_spec.rb | 24 +++++++++++++++++++
3 files changed, 51 insertions(+), 7 deletions(-)
diff --git a/app/controllers/concerns/signature_verification.rb b/app/controllers/concerns/signature_verification.rb
index 5f95fa3461..e5d5e2ca61 100644
--- a/app/controllers/concerns/signature_verification.rb
+++ b/app/controllers/concerns/signature_verification.rb
@@ -22,6 +22,12 @@ module SignatureVerification
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 = {}
@@ -76,7 +82,7 @@ module SignatureVerification
def build_signed_string(signed_headers)
signed_headers = 'date' if signed_headers.blank?
- signed_headers.split(' ').map do |signed_header|
+ 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'
@@ -87,6 +93,16 @@ module SignatureVerification
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
diff --git a/app/lib/formatter.rb b/app/lib/formatter.rb
index 8b694536c2..35d5a09b76 100644
--- a/app/lib/formatter.rb
+++ b/app/lib/formatter.rb
@@ -90,8 +90,12 @@ class Formatter
private
+ def html_entities
+ @html_entities ||= HTMLEntities.new
+ end
+
def encode(html)
- HTMLEntities.new.encode(html)
+ html_entities.encode(html)
end
def encode_and_link_urls(html, accounts = nil, options = {})
@@ -143,7 +147,7 @@ class Formatter
emoji = emoji_map[shortcode]
if emoji
- replacement = "<img draggable=\"false\" class=\"emojione\" alt=\":#{shortcode}:\" title=\":#{shortcode}:\" src=\"#{emoji}\" />"
+ replacement = "<img draggable=\"false\" class=\"emojione\" alt=\":#{encode(shortcode)}:\" title=\":#{encode(shortcode)}:\" src=\"#{encode(emoji)}\" />"
before_html = shortname_start_index.positive? ? html[0..shortname_start_index - 1] : ''
html = before_html + replacement + html[i + 1..-1]
i += replacement.size - (shortcode.size + 2) - 1
@@ -212,7 +216,7 @@ class Formatter
return link_to_account(acct) unless linkable_accounts
account = linkable_accounts.find { |item| TagManager.instance.same_acct?(item.acct, acct) }
- account ? mention_html(account) : "@#{acct}"
+ account ? mention_html(account) : "@#{encode(acct)}"
end
def link_to_account(acct)
@@ -221,7 +225,7 @@ class Formatter
domain = nil if TagManager.instance.local_domain?(domain)
account = EntityCache.instance.mention(username, domain)
- account ? mention_html(account) : "@#{acct}"
+ account ? mention_html(account) : "@#{encode(acct)}"
end
def link_to_hashtag(entity)
@@ -239,10 +243,10 @@ class Formatter
end
def hashtag_html(tag)
- "<a href=\"#{tag_url(tag.downcase)}\" class=\"mention hashtag\" rel=\"tag\">#<span>#{tag}</span></a>"
+ "<a href=\"#{encode(tag_url(tag.downcase))}\" class=\"mention hashtag\" rel=\"tag\">#<span>#{encode(tag)}</span></a>"
end
def mention_html(account)
- "<span class=\"h-card\"><a href=\"#{TagManager.instance.url_for(account)}\" class=\"u-url mention\">@<span>#{account.username}</span></a></span>"
+ "<span class=\"h-card\"><a href=\"#{encode(TagManager.instance.url_for(account))}\" class=\"u-url mention\">@<span>#{encode(account.username)}</span></a></span>"
end
end
diff --git a/spec/controllers/concerns/signature_verification_spec.rb b/spec/controllers/concerns/signature_verification_spec.rb
index 3daf1fc4e8..7206900971 100644
--- a/spec/controllers/concerns/signature_verification_spec.rb
+++ b/spec/controllers/concerns/signature_verification_spec.rb
@@ -73,6 +73,30 @@ describe ApplicationController, type: :controller do
end
end
+ context 'with request older than a day' do
+ before do
+ get :success
+
+ fake_request = Request.new(:get, request.url)
+ fake_request.add_headers({ 'Date' => 2.days.ago.utc.httpdate })
+ fake_request.on_behalf_of(author)
+
+ request.headers.merge!(fake_request.headers)
+ end
+
+ describe '#signed_request?' do
+ it 'returns true' do
+ expect(controller.signed_request?).to be true
+ end
+ end
+
+ describe '#signed_request_account' do
+ it 'returns nil' do
+ expect(controller.signed_request_account).to be_nil
+ end
+ end
+ end
+
context 'with body' do
before do
post :success, body: 'Hello world'