CVE-2015-5963

aka Empty Crowd Wipeout

CVE: CVE-2015-5963
CWE: 459
ipc:
  note: This is a DoS attack from making repeated logout requests.
  answer: false
  question: |
    Did the feature that this vulnerability affected use inter-process
    communication? IPC includes OS signals, pipes, stdin/stdout, message
    passing, and clipboard. Writing to files that another program in this
    software system reads is another form of IPC.

    Answer should be boolean.
CVSS: AV:N/AC:L/Au:N/C:N/I:N/A:P
bugs: []
i18n:
  note: |
    There was a comment about an existing ticket on preserving the language,
    which is stored in the session, upon logout.
  answer: true
  question: |
    Was the feature impacted by this vulnerability about internationalization
    (i18n)? An internationalization feature is one that enables people from all
    over the world to use the system. This includes translations, locales,
    typography, unicode, or various other features.

    Answer should be boolean. Write a note about how you came to the conclusions
    you did.
repo: 
vccs:
- note: |
    (2008-08-13) flush() on session cleans out session and recreates key. Provide
    fresh session on logout.
  commit: 5e8efa9a6032f9c4278199ab354c3ff742387263
- note: "(2005-08-16) Repeatedly try logging out until session is cleared.\n"
  commit: '07889c13a63eeb3e8a73f1e02a21227def3ae548'
- note: "(2008-06-07) Can get/set expiry for sessions.\n"
  commit: 8d4f79a799136edf8190c357e3e0497d7db3ad77
- note: |
    (2013-08-19) When logging out/ending a session, don't create a new, empty
    session. Achieves this by setting the session key to the empty string.
  commit: 393c0e24223c701edeb8ce7dc9d0f852f0c081ad
fixes:
- note: |
    (2015-08-05) In 1.4.x, ensure that cookies are not set in response when session
    is empty. Also, prevent empty sessions from being created on flush(). Achieves
    this by setting self._session_key to None. Added tests.
  commit: 575f59f9bc7c59a5e41a081d1f5f55fc859c5012
- note: |
    (2015-08-05) In 1.7.x, ensure that cookies are not set in response when session
    is empty. Also, prevent empty sessions from being created on flush(). Achieves
    this by setting self._session_key to None. Added tests.
  commit: 2f5485346ee6f84b4e52068c04e043092daf55f7
- note: |
    (2015-08-05) In 1.8.x, ensure that cookies are not set in response when session
    is empty. Added tests.
  commit: 2eb86b01d7b59be06076f6179a454d0fd0afaff6
bounty:
  amt: 
  url: 
  announced: 
lessons:
  yagni:
    note: 
    applies: false
  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: false
  complex_inputs:
    note: 
    applies: false
  distrust_input:
    note: 
    applies: false
  least_privilege:
    note: 
    applies: false
  native_wrappers:
    note: 
    applies: false
  defense_in_depth:
    note: 
    applies: false
  detect_and_record:
    note: |
      Log requests to see if someone is trying to spam the system to
      case a DoS.
    applies: true
  secure_by_default:
    note: 
    applies: false
  environment_variables:
    note: 
    applies: false
  security_by_obscurity:
    note: 
    applies: false
  frameworks_are_optional:
    note: 
    applies: false
reviews: []
sandbox: 
upvotes: 30
CWE_note: |
  When sessions are flushed, they should not recreate new sessions, leading to
  possible DoS.
mistakes:
  answer: |
    A little bit of it was miscommunication on what logging out really means for
    a session and its data. A design mistake was made as well by having sessions
    call self.create() when flushing. The mitigation proposed by the CWE mentions
    deletion after something is no longer needed. A session should be deleted upon
    logout, and a new one should not be made.
  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: Empty Crowd Wipeout
subsystem:
  name:
  - backends
  - http
  - db
  answer: path
  question: |
    What subsystems was the mistake in?

    Most systems don't have a formal list of their subsystems, but you can
    usually infer them from path names, bug report tags, or other key words
    used. A single source file is not what we mean by a subsystem. In Django,
    the "Component" field on the bug report is useful. But there may be other
    subsystems involved.

    Your subsystem name(s) should not have any dots or slashes in them. Only
    alphanumerics, whitespace, _, - and @.Feel free to add multiple using a YAML
    array.

    In the answer field, explain where you saw these words.
    In the name field, a subsystem name (or an array of names)

    e.g. clipboard, model, view, controller, mod_dav, ui, authentication
discovered:
  answer: |
    Reported by Lin Hua Cheng. Possible discovery due to realization that logging explicitly means
    that session data should not be preserved. No other information regarding discovery is given.
  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, contest, and developer flags can be true, false, or nil.

    If there is no evidence as to how this vulnerability was found, then please explain where you looked.
  automated: false
  developer: false
description: |
  Someone can repeatedly make logout requests, which would cause many new empty
  sessions to be created. This can result in an interruption in service availability
  by filling up the session store, and it can cause other users' session records to
  be evicted.
unit_tested:
  fix: true
  code: true
  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 code: and fix: - your answer should be boolean.

    For the code_answer below, look not only at the fix but the surrounding
    code near the fix in related directories and determine if and was there were unit tests involved for this subsystem. The code

    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.
  fix_answer: |
    New tests were made to ensure session deletion occurred when taking an action
    that would result in the session ending, in addition to ensuring that flushing
    an empty session without a session cookie wouldn't set a cookie.
  code_answer: |
    Unit tests did exist, but they did not test for the lack of a session upon logout,
    as that was not part of the design.
discoverable: 
reported_date: 
specification:
  answer: false
  answer_note: |
    No specification is mentioned; just that logging out explicitly means
    session data should not be preserved.
  instructions: |
    Is there mention of a violation of a specification? For example,
    an RFC specification, a protocol specification, or a requirements
    specification.

    Be sure to check all artifacts for this: bug report, security
    advisory, commit message, etc.

    The answer field should be boolean. In answer_note, please explain
    why you come to that conclusion.
announced_date: 2015-08-24T14:59Z
curation_level: 1
published_date: '2015-08-24'
CWE_instructions: |
  Please go to http://cwe.mitre.org and find the most specific, appropriate CWE
  entry that describes your vulnerability. We recommend going to
  https://cwe.mitre.org/data/definitions/699.html for the Software Development
  view of the vulnerabilities. We also recommend the tool
  http://www.cwevis.org/viz to help see how the classifications work.

  If you have anything to note about why you classified it this way, write
  something in CWE_note. This field is optional.

  Just the number here is fine. No need for name or CWE prefix. If more than one
  apply here, then choose the best one and mention the others in CWE_note.
yaml_instructions: |
  ===YAML Primer===
  This is a dictionary data structure, akin to JSON.
  Everything before a colon is a key, and the values here are usually strings
  For one-line strings, you can just use quotes after the colon
  For multi-line strings, as we do for our instructions, you put a | and then
  indent by two spaces

  For readability, we hard-wrap multi-line strings at 80 characters. This is
  not absolutely required, but appreciated.
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:
  commits:
  - note: |
      (2009-01-10) This commit introduces cached, dataase-backed sessions. This has
      the same issue as the regular session with calling self.create() on flush().
      This means that the same specific part of the vulnerability existed in two files.
    commit: 299e1e814fa7c5f8033872213b8876fc12fcd7be
  - note: |
      (2015-05-11) On flush(), the original cause of the vulnerability came from
      self.create(). Another commit changed this line to setting self._session_key
      to ''. This apparently wasn't good enough, as 2 years later, this commit changed
      that to set self._session_key to None. No explanation for why this fix was needed.
    commit: '088579638b160f3716dc81d194be70c72743593f'
  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?
curated_instructions: |
  If you are manually editing this file, then you are "curating" it.

  Set the version number that you were given in your instructions.

  This will enable additional editorial 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 properly updated.
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.
nickname_instructions: |
  A catchy name for this vulnerability that would draw attention it. If the
  report mentions a nickname, use that. Must be under 30 characters.
  Optional.
reported_instructions: |
  What date was the vulnerability reported to the security team? Look at the
  security bulletins and bug reports. It is not necessarily the same day that the
  CVE was created.  Leave blank if no date is given.
  Please enter your date in YYYY-MM-DD format.
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.
published_instructions: |
  Is there a published fix or patch date for this vulnerability?
  Please enter your date in YYYY-MM-DD 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 project-specific
  stuff. Remove references to versions, specific filenames, and other jargon
  that outsiders to this project would not understand. Technology like "regular
  expressions" is fine, and security phrases like "invalid write" are fine to
  keep too.

  Your target audience is people just like you before you took any course in
  security