CVE-2014-7930

CVE: CVE-2014-7930
CWE:
- 416
bugs:
- 442806
repo: 
vccs:
- note: |
    This is the commit that introduced the vulnerability. This user was attempting to resolve another
    bug, specifically, "Avoid O(N^2) in worst case when pre-calculating event.path for each TreeScope."
    It is very interesting that the patch to one bug introduced another.
  commit: 5949a17dd1ade8a48d177180909c404f40319cfe
fixes:
- note: ''
  commit: 388118e6169b92a1de01ab2988610464a26eaaf9
bounty:
  date: '2015-01-21 15:11:00.000000000 -05:00'
  amount: 3000.0
  references:
  - http://chromereleases.googleblog.com/2015/01/stable-update.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: |
      The whole premise of this bug is that a malicious user could try to access memory that had already been freed.
      By sanitizing and validating all user input, the developers were able to determine if that happening and prevent it.
    applies: true
  least_privilege:
    note: |
      End Chrome users should not have access to the make calls to the freed memory addressed
      EDIT... this was determined out of scope
    applies: false
  native_wrappers:
    note: 
    applies: 
  defense_in_depth:
    note: This lesson is applicable as the system should run security checks at several
      levels, even redundantly, to ensure the system has not been exploited.
    applies: true
  secure_by_default:
    note: 
    applies: 
  environment_variables:
    note: 
    applies: 
  security_by_obscurity:
    note: "As this vulnerability exploits system level DOM objects, the proper outer
      layers of security\ncould, in theory, protect from this. For example, if you
      can prove that all system variables are fully encapsulated and\ntherefore inaccessible
      to outside users, you could claim to be secure from exploitations of this vulnerability.
      \n"
    applies: true
  frameworks_are_optional:
    note: 
    applies: 
reviews:
- 834093002
- 794123004
upvotes: 
mistakes:
  answer: "The user who committed the VCC introduced this vulnerability in his own
    code. \nHowever, since the concern is that different event contexts require the
    TreeScope at \ndifferent times, it can be argued that this is a Design mistake
    first and foremost. \nPointers to the root node of a DOM object should be null
    after the root has been deleted.\nIn this case the mitigation solution was to
    store a backup to the rootNode of\nthe tree. Developers should have taken into
    account for the tight coupling between these\ntwo contexts, and the possiblity
    that actions in one scope would have catastrophic effects \non another. This is
    more of a band-aid fix that doesn't fully adress the fact that the \nscope of
    these variable should not be so tightly coupled. \n"
  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.
announced: '2015-01-22 17:59:11.977000000 -05:00'
subsystem:
  name: dom
  answer: Based on the description in the CVE and blog post
  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: '2014-12-16'
  answer: "Found using ClusterFuzz then reproduced by hand.\nBelow is the post made
    on https://bugs.chromium.org/p/chromium/issues/detail?id=442806-\n\"Confirmed.
    I could reproduce this.\nThe root cause is that TreeScopeEventContext::m_treeScope
    is not a RefPtr.\nWe should make TreeScope *RefCounted* somehow. I'm not sure
    this is a good idea.\nMaybe we can have another idea. \" -hayato@chromium.org
    \n"
  google: true
  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: true
description: "The vulnerability was in Blink, Google Chrome's browser engine, in a
  DOM \nimplementation of a tree data structure written in C. \n\nA DOM model represents
  a document with a logical tree. Each branch of the \ntree ends in a node, and each
  node contains objects. DOM methods allow \nprogrammatic access to the tree. \n\nThe
  cause of this vulnerability was that it was possible for a variable called \nTreeScope,
  which represents a DOM object root node, to be deleted while it was\nstill in use
  in another context. \n\nThis created a use-after-free vulnerability. Use After Free
  refers to the \nattempt to access memory after it has been freed, which can cause
  a program to crash\nin the best case, or can potentially result in the execution
  of \narbitrary code or even enable full remote code execution capabilities.\n\nFurthermore,
  crafted JavaScript code could trigger improper maintenance of TreeScope data through
  this vulnerability.\n"
unit_tested:
  fix: true
  code: true
  answer: "The VCC does include fairly extensive unit-testing. \nHowever, it is only
    testing performance as that was the bug being resolved in this commit.\nBoth commits
    dedicated to fixing the Use After Free flaw did include the proper unit testing
    for this vulnerability. \n"
  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 during this time.
  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 the first attempt to fix the bug. The developer added additional
      checks to ensure a null pointer \nwas not being acessed. This commit is interesting
      as it contains huge edits to test files,\nbut only 5 additions and 1 deletion
      from the actual C file. This shows that the fix was not very complex,\nbut did
      require extensive testing to ensure edge case coverage.\n"
    commit: 3a6fd28a6ce60c3ab3005e70ae5fb09eeb60a5fb
  - 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.