CVE-2014-1748

aka Scroll Paint Spatter

CVE: CVE-2014-1748
CWE:
- 829
bugs:
- 331168
repo: 
vccs:
- note: |
    Added 'visibleAreaWithScrollbars', but did not clip the area, allowing it to
    be tampered with if the child passed up extremely large dimensions.
  commit: 6e6884c5a253d1f018f435ad6137e7c4cf309d28
fixes:
- note: Fixed scrollbar not properly clipping to correct size
  commit: 73b4ef442741fad55c547f053b8c6b6eb93ce3aa
bounty:
  date: '2014-05-20'
  amount: 500.0
  references:
  - http://chromereleases.googleblog.com/2014/05/stable-channel-update_20.html
lessons:
  yagni:
    note: 
    applies: 
  question: |
    Are there any common lessons we have learned from class that apply to this
    vulnerability? In other words, could this vulnerability serve as an example
    of one of those lessons?

    Leave "applies" blank or put false if you did not see that lesson (you do
    not need to put a reason). Put "true" if you feel the lesson applies and put
    a quick explanation of how it applies.

    Don't feel the need to claim that ALL of these apply, but it's pretty likely
    that one or two of them apply.

    If you think of another lesson we covered in class that applies here, feel
    free to give it a small name and add one in the same format as these.
  serial_killer:
    note: 
    applies: 
  complex_inputs:
    note: 
    applies: 
  distrust_input:
    note: 
    applies: 
  least_privilege:
    note: 
    applies: 
  native_wrappers:
    note: 
    applies: 
  defense_in_depth:
    note: 
    applies: 
  secure_by_default:
    note: 
    applies: 
  environment_variables:
    note: 
    applies: 
  security_by_obscurity:
    note: 
    applies: 
  frameworks_are_optional:
    note: 
    applies: 
reviews:
- 245543002
- 220243010
upvotes: 40
mistakes:
  answer: |
    The main mistake that was made here was less of a mistake and more of an
    oversight. The vulnerability was introduced when ScrollView::paint() needed
    to be clipped by the visible content (visibleContentRect), but it was never
    checked that the scrollbar was also clipped as well, leading to an inconsistency
    between the two parts of the feature.

    This was most likely missed due to the issue being with extremely large dimensions
    being specified for the elements. It is unclear how big these must have been to
    trigger the vulnerability, so to originally test it would have probably needed to be
    through manual (or possibly fuzzer) investigation. Tests were added specifically
    to check for this issue when the code was fixed in order to prevent the same issue
    popping up again.

    The fix here appears to be a proper fix, as the scrollbar is now properly clipped
    to the same size as the rect mentioned above.
  question: |
    In your opinion, after all of this research, what mistakes were made that
    led to this vulnerability? Coding mistakes? Design mistakes?
    Maintainability? Requirements? Miscommunications?

    Look at the CWE entry for this vulnerability and examine the mitigations
    they have written there. Are they doing those? Does the fix look proper?

    Use those questions to inspire your answer. Don't feel obligated to answer
    every one. Write a thoughtful entry here that those ing the software
    engineering industry would find interesting.
nickname: Scroll Paint Spatter
announced: '2014-05-21 07:14:09.863000000 -04:00'
subsystem:
  name: Webkit
  answer: Based on the description in the CVE and Code
  question: |
    What subsystems was the mistake in?

    Look at the path of the source code files code that were fixed to get
    directory names. Look at comments in the code. Look at the bug reports how
    the bug report was tagged. Examples: "clipboard", "gpu", "ssl", "speech", "renderer"
discovered:
  date: '2013-12-31'
  answer: This vulnerability was found by 3rd party developers
  google: false
  contest: false
  question: |
    How was this vulnerability discovered?

    Go to the bug report and read the conversation to find out how this was
    originally found. Answer in longform below in "answer", fill in the date in
    YYYY-MM-DD, and then determine if the vulnerability was found by a Google
    employee (you can tell from their email address). If it's clear that the
    vulenrability was discovered by a contest, fill in the name there.

    The "automated" flag can be true, false, or nil.
    The "google" flag can be true, false, or nil.

    If there is no evidence as to how this vulnerability was found, then you may
    leave the entries blank except for "answer". Write down where you looked in "answer".
  automated: false
description: |
  The scrollbar rectangles for images were not properly being clipped to the the
  parent document that they interacted with (owning viewport). This non-limiting
  effect allowed for chiled documents to draw/cover over the respective parent
  documents by passing extremely large dimensions to for the scrollbar elements.
  An attacker could use this by creating a transparent child document that covered
  the parent. This could allow the attacker to spoof content or cause the
  user to click on malicious links.
unit_tested:
  fix: true
  code: true
  answer: |
    From looking at the fix code it's clear that code was tested and they added
    two new tests for fixing this vulnerability.
  question: |
    Were automated unit tests involved in this vulnerability?
    Was the original code unit tested, or not unit tested? Did the fix involve
    improving the automated tests?

    For the "code" answer below, look not only at the fix but the surrounding
    code near the fix and determine if and was there were unit tests involved
    for this module.

    For the "fix" answer below, check if the fix for the vulnerability involves
    adding or improving an automated test to ensure this doesn't happen again.
major_events:
  answer: |
    I did not see any major events, just minor additions to the method and some
    refactoring, along with the above mentioned interesting commit.
  events:
  - date: 
    name: 
  - date: 
    name: 
  question: |
    Please record any major events you found in the history of this
    vulnerability. Was the code rewritten at some point? Was a nearby subsystem
    changed? Did the team change?

    The event doesn't need to be directly related to this vulnerability, rather,
    we want to capture what the development team was dealing with at the time.
curation_level: 1
CWE_instructions: |
  Please go to cwe.mitre.org and find the most specific, appropriate CWE entry
  that describes your vulnerability. (Tip: this may not be a good one to start
  with - spend time understanding this vulnerability before making your choice!)
bounty_instructions: |
  If you came across any indications that a bounty was paid out for this
  vulnerability, fill it out here. Or correct it if the information already here
  was wrong. Otherwise, leave it blank.
interesting_commits:
  answer: 
  commits:
  - note: |
      This was a large refactoring, in which the boolean argument to visibleContentRect
      was replated with an enum, affecting a large number of files.
    commit: 8b8dec2806e1e847eb31b454fa4b20e01d12d374
  - note: 
    commit: 
  question: |
    Are there any interesting commits between your VCC(s) and fix(es)?

    Write a brief (under 100 words) description of why you think this commit was
    interesting in light of the lessons learned from this vulnerability. Any
    emerging themes?

    If there are no interesting commits, demonstrate that you completed this section by explaining what happened between the VCCs and the fix.
curated_instructions: |
  If you are manually editing this file, then you are "curating" it. Set the
  entry below to "true" as soon as you start. This will enable additional
  integrity checks on this file to make sure you fill everything out properly.
  If you are a student, we cannot accept your work as finished unless curated is
  set to true.
upvotes_instructions: |
  For the first round, ignore this upvotes number.

  For the second round of reviewing, you will be giving a certain amount of
  upvotes to each vulnerability you see. Your peers will tell you how
  interesting they think this vulnerability is, and you'll add that to the
  upvotes score on your branch.
announced_instructions: |
  Was there a date that this vulnerability was announced to the world? You can
  find this in changelogs, blogs, bug reports, or perhaps the CVE date. A good
  source for this is Chrome's Stable Release Channel
  (https://chromereleases.googleblog.com/).
  Please enter your date in YYYY-MM-DD format.
fixes_vcc_instructions: |
  Please put the commit hash in "commit" below (see my example in
  CVE-2011-3092.yml). Fixes and VCCs follow the same format.
description_instructions: |
  You can get an initial description from the CVE entry on cve.mitre.org. These
  descriptions are a fine start, but they can be kind of jargony.

  Rewrite this description in your own words. Make it interesting and easy to
  read to anyone with some programming experience. We can always pull up the NVD
  description later to get more technical.

  Try to still be specific in your description, but remove Chromium-specific
  stuff. Remove references to versions, specific filenames, and other jargon
  that outsiders to Chromium would not understand. Technology like "regular
  expressions" is fine, and security phrases like "invalid write" are fine to
  keep too.