CVE-2015-2963 (published 2015-07-10T17:59Z)

The thoughtbot paperclip gem before 4.2.2 for Ruby does not consider the content-type value during media-type validation, which allows remote attackers to upload HTML documents and conduct cross-site scripting (XSS) attacks via a spoofed value, as demonstrated by image/jpeg.

Severity: MEDIUM
CVSS v2 base score: 4.3 (AV:N/AC:M/Au:N/C:N/I:P/A:N)

Weakness information:
cwe_id: CWE-79
cwe_name: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
description: The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
extended_description: 
            Cross-site scripting (XSS) vulnerabilities occur when:
            
               Untrusted data enters a web application, typically from a web request.
               The web application dynamically generates a web page that contains this untrusted data.
               During page generation, the application does not prevent the data from containing content that is executable by a web browser, such as JavaScript, HTML tags, HTML attributes, mouse events, Flash, ActiveX, etc.
               A victim visits the generated web page through a web browser, which contains malicious script that was injected using the untrusted data.
               Since the script comes from a web page that was sent by the web server, the victim's web browser executes the malicious script in the context of the web server's domain.
               This effectively violates the intention of the web browser's same-origin policy, which states that scripts in one domain should not be able to access resources or run code in a different domain.
            
            There are three main kinds of XSS:
            
               
                  Type 1: Reflected XSS (or Non-Persistent) - 
         			The server reads data directly from the HTTP request and reflects it back in the HTTP response. Reflected XSS exploits occur when an attacker causes a victim to supply dangerous content to a vulnerable web application, which is then reflected back to the victim and executed by the web browser. The most common mechanism for delivering malicious content is to include it as a parameter in a URL that is posted publicly or e-mailed directly to the victim. URLs constructed in this manner constitute the core of many phishing schemes, whereby an attacker convinces a victim to visit a URL that refers to a vulnerable site. After the site reflects the attacker's content back to the victim, the content is executed by the victim's browser.
               
                  Type 2: Stored XSS (or Persistent) - 
               The application stores dangerous data in a database, message forum, visitor log, or other trusted data store. At a later time, the dangerous data is subsequently read back into the application and included in dynamic content. From an attacker's perspective, the optimal place to inject malicious content is in an area that is displayed to either many users or particularly interesting users. Interesting users typically have elevated privileges in the application or interact with sensitive data that is valuable to the attacker. If one of these users executes malicious content, the attacker may be able to perform privileged operations on behalf of the user or gain access to sensitive data belonging to the user. For example, the attacker might inject XSS into a log message, which might not be handled properly when an administrator views the logs.
            
               
                  Type 0: DOM-Based XSS - 
               In DOM-based XSS, the client performs the injection of XSS into the page; in the other types, the server performs the injection. DOM-based XSS generally involves server-controlled, trusted script that is sent to the client, such as Javascript that performs sanity checks on a form before the user submits it. If the server-supplied script processes user-supplied data and then injects it back into the web page (such as with dynamic HTML), then DOM-based XSS is possible.
            
            
            Once the malicious script is injected, the attacker can perform a variety of malicious activities. The attacker could transfer private information, such as cookies that may include session information, from the victim's machine to the attacker. The attacker could send malicious requests to a web site on behalf of the victim, which could be especially dangerous to the site if the victim has administrator privileges to manage that site. Phishing attacks could be used to emulate trusted web sites and trick the victim into entering a password, allowing the attacker to compromise the victim's account on that web site. Finally, the script could exploit a vulnerability in the web browser itself possibly taking over the victim's machine, sometimes referred to as "drive-by hacking."
            In many cases, the attack can be launched without the victim even being aware of it. Even with careful users, attackers frequently use a variety of methods to encode the malicious portion of the attack, such as URL encoding or Unicode, so the request looks less suspicious.
         
         

Fix information:
repo_url: https://github.com/thoughtbot/paperclip
commit_details: repo_url: https://github.com/thoughtbot/paperclip
author: Jon Yurek
author_date: 2015-05-22 15:21:01-04:00
msg: Fix a possible security issue with spoofing

Thanks to MORI Shingo of DeNA Co., Ltd. for reporting this.

There is an issue where if an HTML file is uploaded with a .html
extension, but the content type is listed as being `image/jpeg`, this
will bypass a validation checking for images. But it will also pass the
spoof check, because a file named .html and containing actual HTML
passes the spoof check.

This change makes it so that we also check the supplied content type. So
even if the file contains HTML and ends with .html, it doesn't match the
content type of `image/jpeg` and so it fails.
repository: repo_url: https://github.com/thoughtbot/paperclip
repo_name: thoughtbot/paperclip
description: Easy file attachment management for ActiveRecord
repo_language: Ruby
owner: thoughtbot
file_changes: filename: NEWS
change_type: ModificationType.MODIFY
diff: @@ -1,3 +1,7 @@
+New in 4.2.2:
+
+* Security fix: Fix a potential security issue with spoofing
+
 New in 4.2.1:
 
 * Improvement: Added `validate_media_type` options to allow/bypass spoof check

programming_language: Markdown
filename: en.yml
change_type: ModificationType.MODIFY
diff: @@ -2,7 +2,7 @@ en:
   errors:
     messages:
       in_between: "must be in between %{min} and %{max}"
-      spoofed_media_type: "has an extension that does not match its contents"
+      spoofed_media_type: "has contents that are not what they are reported to be"
 
   number:
     human:

programming_language: CoffeeScript
filename: media_type_spoof_detector.rb
change_type: ModificationType.MODIFY
diff: @@ -1,18 +1,21 @@
 module Paperclip
   class MediaTypeSpoofDetector
-    def self.using(file, name)
-      new(file, name)
+    def self.using(file, name, content_type)
+      new(file, name, content_type)
     end
 
-    def initialize(file, name)
+    def initialize(file, name, content_type)
       @file = file
       @name = name
+      @content_type = content_type || ""
     end
 
     def spoofed?
       if has_name? && has_extension? && media_type_mismatch? && mapping_override_mismatch?
-        Paperclip.log("Content Type Spoof: Filename #{File.basename(@name)} (#{supplied_file_content_types}), content type discovered from file command: #{calculated_content_type}. See documentation to allow this combination.")
+        Paperclip.log("Content Type Spoof: Filename #{File.basename(@name)} (#{supplied_content_type} from Headers, #{content_types_from_name} from Extension), content type discovered from file command: #{calculated_content_type}. See documentation to allow this combination.")
         true
+      else
+        false
       end
     end
 
@@ -27,35 +30,44 @@ module Paperclip
     end
 
     def media_type_mismatch?
-      ! supplied_file_media_types.include?(calculated_media_type)
+      supplied_type_mismatch? || calculated_type_mismatch?
+    end
+
+    def supplied_type_mismatch?
+      supplied_media_type.present? && !media_types_from_name.include?(supplied_media_type)
+    end
+
+    def calculated_type_mismatch?
+      !media_types_from_name.include?(calculated_media_type)
     end
 
     def mapping_override_mismatch?
       mapped_content_type != calculated_content_type
     end
 
-    def supplied_file_media_types
-      @supplied_file_media_types ||= MIME::Types.type_for(@name).collect(&:media_type)
+
+    def supplied_content_type
+      @content_type
     end
 
-    def calculated_media_type
-      @calculated_media_type ||= calculated_content_type.split("/").first
+    def supplied_media_type
+      @content_type.split("/").first
     end
 
-    def supplied_file_content_types
-      @supplied_file_content_types ||= MIME::Types.type_for(@name).collect(&:content_type)
+    def content_types_from_name
+      @content_types_from_name ||= MIME::Types.type_for(@name)
     end
 
-    def calculated_content_type
-      @calculated_content_type ||= type_from_file_command.chomp
+    def media_types_from_name
+      @media_types_from_name ||= content_types_from_name.collect(&:media_type)
     end
 
-    def mapped_content_type
-      Paperclip.options[:content_type_mappings][filename_extension]
+    def calculated_content_type
+      @calculated_content_type ||= type_from_file_command.chomp
     end
 
-    def filename_extension
-      File.extname(@name.to_s.downcase).sub(/^\./, '').to_sym
+    def calculated_media_type
+      @calculated_media_type ||= calculated_content_type.split("/").first
     end
 
     def type_from_file_command
@@ -65,5 +77,13 @@ module Paperclip
         ""
       end
     end
+
+    def mapped_content_type
+      Paperclip.options[:content_type_mappings][filename_extension]
+    end
+
+    def filename_extension
+      File.extname(@name.to_s.downcase).sub(/^\./, '').to_sym
+    end
   end
 end

programming_language: Ruby
filename: media_type_spoof_detection_validator.rb
change_type: ModificationType.MODIFY
diff: @@ -5,7 +5,7 @@ module Paperclip
     class MediaTypeSpoofDetectionValidator < ActiveModel::EachValidator
       def validate_each(record, attribute, value)
         adapter = Paperclip.io_adapters.for(value)
-        if Paperclip::MediaTypeSpoofDetector.using(adapter, value.original_filename).spoofed?
+        if Paperclip::MediaTypeSpoofDetector.using(adapter, value.original_filename, value.content_type).spoofed?
           record.errors.add(attribute, :spoofed_media_type)
         end
       end

programming_language: Ruby
filename: media_type_spoof_detector_spec.rb
change_type: ModificationType.MODIFY
diff: @@ -43,4 +43,14 @@ describe Paperclip::MediaTypeSpoofDetector do
       Paperclip.options[:content_type_mappings] = {}
     end
   end
+
+  it "rejects a file if named .html and is as HTML, but we're told JPG" do
+    file = File.open(fixture_file("empty.html"))
+    assert Paperclip::MediaTypeSpoofDetector.using(file, "empty.html", "image/jpg").spoofed?
+  end
+
+  it "does not reject is content_type is empty but otherwise checks out" do
+    file = File.open(fixture_file("empty.html"))
+    assert ! Paperclip::MediaTypeSpoofDetector.using(file, "empty.html", "").spoofed?
+  end
 end

programming_language: Ruby
filename: media_type_spoof_detection_validator_spec.rb
change_type: ModificationType.MODIFY
diff: @@ -30,7 +30,7 @@ describe Paperclip::Validators::MediaTypeSpoofDetectionValidator do
     Paperclip::MediaTypeSpoofDetector.stubs(:using).returns(detector)
     @validator.validate(@dummy)
 
-    assert_equal "has an extension that does not match its contents", @dummy.errors[:avatar].first
+    assert_equal I18n.t("errors.messages.spoofed_media_type"), @dummy.errors[:avatar].first
   end
 
   it "runs when attachment is dirty" do

programming_language: Ruby