CVE-2011-2834

CVE: CVE-2011-2834
CWE:
- 415
bugs:
- 93472
repo: 
vccs:
- note: 'This is the initial commit of the third party libraries to the repository.

    '
  commit: 584cd5cbd7be997400ccb8db24ae5410b0b88117
- note: Updating libxml to 2.7.7
  commit: a850e9592bb1a8c43275116ff565c91b4b1cb66b
fixes:
- note: ''
  commit: 3a766e0115e9799db766a88554b9ab12ee5bf2a4
bounty:
  date: '2011-09-16'
  amount: 1000.0
  references:
  - http://chromereleases.googleblog.com/2011/09/stable-channel-update_16.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: 
  free_is_not_idempotent:
    note: 'The vulnerability was caused by calling free twice on the same memory address.

      '
    applies: true
  frameworks_are_optional:
    note: 
    applies: 
reviews:
- 7793001
- 7747031
upvotes: 6
mistakes:
  answer: |-
    The reason this vulnerability existed was a coding mistake. Objects were being freed twice, but in separate locations. This made it very hard to detect the double free vulnerability in the first place. The developers should have been extra cautious when freeing the objects and spent more time tracing through the code to identify the issue. A static analysis tool could have also been utilized to search for double free instances.

    Another, perhaps better mitigation would have been to set the pointer to the object to NULL after freeing it to ensure that it was not freed twice.

    The fix does not look proper. Error states were added to prevent the code from entering the code block that causes the double free. But, the fix doesn't remove the possibility of the double free. If an attacker was able to manipulate the state of the system and avoid entering the error state, the double free would still be possible.

    The developers fixed multiple related double free issues within the same source code file. It would have been smart for them to check the rest of the file for any other double free vulnerabilities when they were fixing the first issue instead of fixing the issues one by one.
  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: '2011-09-19'
subsystem:
  name: libxml
  answer: Based on the CVE and the bug report.
  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: '2011-08-19'
  answer: 'No information on how this vulnerability was originally found. There are
    steps in the bug report on how to reproduce it.

    '
  google: false
  contest: 
  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: 
description: "A vulnerability where a memory address is freed twice, called a \"double
  free\". \n\nFound in libmxl2, the XML parsing library that Chromium is using.\n\nThis
  vulverability can allow attackers to cause a \"denial of service\" attack, where
  some set of users is no longer able to use the browser. It is not known what sequence
  of activities could lead to an exploit of this vulnerability.\n"
unit_tested:
  fix: true
  code: true
  answer: 'From reading comments on the Chromium issue, it seems that unit tests were
    involved in the vulnerability. It''s not apparent if the original code was unit
    tested or not. The fix commit did not involve improving the automated tests. However,
    one of the comments states that after the fix, the code was run through a "new
    round of tests".

    '
  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. However, this bug seemed
    to have existed as soon as libxml was added into the project. I''m sure there
    were some major events during this time period.

    '
  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: 'Commit is a fix for a very similar double free vulnerability. The vulnerability
      was submitted by the same user that submitted the bug report for this issue.

      '
    commit: 4b41418a14d224fcc3dcd8b1b5923920ea709d5c
  - note: 'This commit is a fix for once again a very similar double free bug. Again,
      it was submitted by the same user as this issue. Not sure why the developers
      would not have searched around for other double free issues when fixing these
      two. Several months had passed since the last bug fix, so there was certainly
      time to check for similar bugs.

      '
    commit: c9911bc93097a5df5518f5b88e1d5ed5ef275a4d
  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.