CVE-2020-13776

aka Mr. 0Day

CVE: CVE-2020-13776
CWE:
- 20
- 681
ipc:
  note: this is directly not an IPC issue at all either
  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:L/AC:H/Au:N/C:C/I:C/A:C
bugs:
- https://github.com/systemd/systemd/issues/15985
- https://github.com/systemd/systemd/issues/6237
i18n:
  note: This should be at all any il8n issue, just a parse issue
  answer: false
  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.
vccs:
- note: Upstream can be found here https://github.com/systemd/systemd/issues/15985.
    Applied to nixpkgs in dbfb40efdd7fed421415620058066bb3e691d735, in https://github.com/NixOS/nixpkgs/pull/91048
  commit: 6300d6fe54bf02405003babc58f658f7fe712b4d
fixes:
- note: 'Only use base 10 for numeric uids/gids #15991'
  commit: 156a5fd297b61bce31630d7a52c15614bf784843
vouch:
  note: |
    There deffiently was more than one person working a long with the issue besides just
    Helio Machado (0x2b3bfa0). GitHub users Adam Nielsen (Malvineous) worked along disucssing
    the issue initialy and trying to solve the problem. Zbigniew Jędrzejewski-Szmek (keszybz) is
    the one who commited the fix https://github.com/systemd/systemd/pull/15991 with Yu Watanabe (yuwata)
    accepting the merge.
    Lennart Poettering (poettering) also was the one who committed parseing tests
    https://github.com/systemd/systemd/pull/16033 with Daan De Meyer (DaanDeMeyer) accepted the merge.
  answer: true
  question: |
    Was there any part of the fix that involved one person vouching for
    another's work?

    This can include:
      * signing off on a commit message
      * mentioning a discussion with a colleague checking the work
      * upvoting a solution on a pull request

    Answer must be true or false.
    Write a note about how you came to the conclusions you did, regardless of what your answer was.
bounty:
  amt: 
  url: 
  announced: 
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: |
      Username input for being decimal and allowed would be somewhat complex input to handle as it should
      handle input value as correct variable. Being C, would cause intersting errors with no type value.
      This was originaly handle but only check for base 10 values. With more complex values (base 8 or 16),
      it failed to check as well. Handling it in base 10 only was the right call the handle the issue as it
      had originaly already solve the prior problem of handling decimal values with CVE-2017-1000082.
    applies: true
  distrust_input:
    note: 
    applies: 
  least_privilege:
    note: 
    applies: 
  native_wrappers:
    note: 
    applies: 
  defense_in_depth:
    note: |
      Being able to keep on checking different values that can be used for user can effect eventualy
      find this error as POSIX included usesage of [a-zA-Z0-9._][a-zA-Z0-9._-]+ which makes hex or octal
      values inclusive and intended.
    applies: true
  secure_by_default:
    note: 
    applies: 
  environment_variables:
    note: 
    applies: 
  security_by_obscurity:
    note: 
    applies: 
  frameworks_are_optional:
    note: 
    applies: 
reviews: []
sandbox:
  note: |
    If not being able to check for user id correctly due to faults of CVE-2020-13776
    it could be considered a root privalage issue that were inteded for the user
  answer: true
  question: |
    Did this vulnerability violate a sandboxing feature that the system
    provides?

    A sandboxing feature is one that allows files, users, or other features
    limited access. Vulnerabilities that violate sandboxes are usually based on
    access control, checking privileges incorrectly, path traversal, and the
    like.

    Answer should be true or false
    Write a note about how you came to the conclusions you did, regardless of
    what your answer was.
upvotes: 25
CWE_note: |
  "CWE 20: Data input received isn't validated properly, wrong numeric base value incorectly passes through as a
   wrong value.
   CWE 681: Incorrect Conversion between Numeric Types, via different numeric base values (wasn't listed on NVD, but
   it still has some similiar properties that makes it relate to it in terms of in proper data type of integer."
mistakes:
  answer: |
    This has to be a design mistake with some planning error backing from fixing the
    CVE-2017-1000082 issue (https://github.com/systemd/systemd/issues/6237). The issue for
    that CVE was first thought to be solved at that time by learning how to handle decimal and digit
    values in username. What was considered at all was how handling any other base number would work
    at all. Specially base 16 and base 8 values. In https://github.com/systemd/systemd/issues/15985,
    a hex input such as 0x2b3bfa0 would cause the CVE-2020-13776 to appear. It also apeared with octal
    values such as 0500 being read as octal due to a leading zero. They were being used also as user
    indetifiers and when tried to check for them, they don't exist due to different interpetation of
    base number values. The fix to this wasn't too complicated as all it needed was to have them be
    use in base 10 and only base 10. https://github.com/systemd/systemd/pull/15991
  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?

    There can, and usually are, many mistakes behind a vulnerability.

    Remember that mistakes can come in many forms:
    * slip: failing to complete a properly planned step due to inattention
              e.g. wrong key in the ignition
              e.g. using < instead of <=
    * lapse: failing to complete a properly planned step due to memory failure
              e.g. forgetting to put car in reverse before backing up
              e.g. forgetting to check null
    * planning error: error that occurs when the plan is inadequate
              e.g. getting stuck in traffic because you didn’t consider the
                   impact of the bridge closing
              e.g. calling the wrong method
              e.g. using a poor design

    These are grey areas, of course. But do your best to analyze the mistakes
    according to this framework.

    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?

    Write a thoughtful entry here that people in the software engineering
    industry would find interesting.
nickname: Mr. 0Day
subsystem:
  name: basic
  note: |
    This are the main files that had the vunlerabilty issue and the effected code within them
    https://github.com/systemd/systemd/issues/15985
    This github link once again shows the effect files and code
  question: |
    What subsystems was the mistake in? These are subsystems WITHIN systemd

    Two areas to look:
      - Bug labels
      - Directory names

    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.

    Example systemd subsystems are:
      * fsck
      * apparmor
      * fstab
      * sd-daemon

    Name should be:
      * all lowercase English letters
      * NOT a specific file
      * can have digits, and _-@/

    Can be multiple subsystems involved, in which case you can make it an array
    e.g.
        name: ["subsystemA", "subsystemB"] # ok
        name: subsystemA # also ok

    Name should be all lowercase, NOT a specific file.
discovered:
  answer: |
    This vulnerability first appear on a github issue post by Helio Machado
    also known as 0x2b3bfa0. They are a google employee. It was also first
    discovered on 2020-05-31. Tho this type of vulnerability is also an extension
    from CVE-2017-1000082 due to an issue that wasn't fully fixed.
  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: true
discussion:
  note: |
    https://github.com/systemd/systemd/issues/6237
    CVE-2017-1000082, the 'parrent' of CVE-2020-13776 as it was a no fully fixed issue for the CVE
    it had quite a bit of discussion of being a serve secruity issue with running at root level.
    Same has been applied and notice with CVE-2020-13776 but not much discussion was found about it
    or talked as a secruity issue unlike CVE-2017-1000082
  question: |
    Was there any discussion surrounding this?

    A discussion can include debates, disputes, or polite talk about how to
    resolve uncertainty.

    Example include:
      * Is this out of our scope?
      * Is this a security?
      * How should we fix this?

    Just because you see multiple comments doesn't mean it's a discussion.
    For example:
      * "Fix line 10". "Ok" is not what we call a discussion
      * "Ping" (reminding people)

    Check the bugs reports, pull requests, and mailing lists archives.

    These answers should be boolean.
      disputed_as_security: true
      any_disagreement: false

    Put any links to disagreements you found in the notes section, or any other
    comment you want to make.
  any_discussion: true
  discussed_as_security: true
stacktrace:
  note: |
    No stacktraces are visiable in the bug reports for this issue besides just
    init issue posted here that was resolved later on with the following commit.
    https://github.com/systemd/systemd/issues/15985
    https://github.com/systemd/systemd/pull/15991
  question: |
    Are there any stacktraces in the bug reports?

    Secondly, if there is a stacktrace, is the fix in the same file that the
    stacktrace points to?

    If there are no stacktraces, then both of these are false - but be sure to
    mention where you checked in the note.

    Answer must be true or false.
    Write a note about how you came to the conclusions you did, regardless of
    what your answer was.
  any_stacktraces: false
  stacktrace_with_fix: false
description: |
  Systemd used to mishandle how numerical usernames get handled.
  Usernames that contain decimal digits or even "0x" followed by hexadecimal
  digits get handled incorectly. The issue exists due to an incomplete fix from
  CVE-2019-1000082 which only fix handling decimal values and not octal (having a
  leading 0 such as 0500 read as 320 in decimal) or hexadecimal such as 0x2b3bfa0.
  The use of 0x0 user accounts were suppose to be an intended feature.
  Successful exploitation of this vulnerability could lead to disclosure of sensitive
  information, addition or modification of data, or Denial of Service (DoS).
unit_tested:
  fix: true
  code: false
  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.

    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: |
    Unit testing for assert checks of parsing different id strings were added not
    long after the vunerabliltiy was found and was decided to be tested against.
    Unit testing commits have also been updated more than once to have more stricter
    testing.
    https://github.com/systemd/systemd/pull/16033  has the parse testing commits
  code_answer: |
    No unit tests were added previously to test the functionality of user strings
    and ids.
specification:
  note: |
    This has effected POSIX spec as it would allowed such characters
    to be entered. User names are allowed to have [a-zA-Z0-9._][a-zA-Z0-9._-]+
    https://github.com/systemd/systemd/issues/15985#issuecomment-636458699
    Above links to a comment from the issue page first seen of CVE-2020-13776
    that mentions about POSIX should allow such characters.
  answer: true
  instructions: |
    Is there mention of a violation of a specification? For example, the POSIX
    spec, an RFC spec, a network protocol spec, or some other requirements
    specification.

    Be sure to check the following artifacts for this:
      * bug reports
      * security advisories
      * commit message
      * pull request
      * mailing lists
      * anything else

    The answer field should be boolean. In answer_note, please explain
    why you come to that conclusion.
announced_date: '2020-05-30'
curation_level: 1
published_date: 2020-06-02'
forgotten_check:
  note: Not a forgeten check really, function can parse values to base 10 and wasn't
    included in param at first
  answer: false
  question: |
    Does the fix for the vulnerability involve adding a forgotten check?

    A "forgotten check" can mean many things. It often manifests as the fix
    inserting an entire if-statement or a conditional to an existing
    if-statement. Or a call to a method that checks something.

    Example of checks can include:
      * null pointer checks
      * check the current role, e.g. root
      * boundary checks for a number
      * consult file permissions
      * check a return value

    Answer must be true or false.
    Write a note about how you came to the conclusions you did, regardless of
    what your answer was.
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 place them in an array like this
    CWE: ["123", "456"] # this is ok
    CWE: [123, 456]     # also ok
    CWE: 123            # also ok
autodiscoverable:
  note: |
    A fuzzer could been able to detect this issue by testing different inputs
    includuing digit values for octal and hex.
  answer: true
  instructions: |
    Is it plausible that a fully automated tool could have discovered
    this? These are tools that require little knowledge of the domain,
     e.g. automatic static analysis, compiler warnings, fuzzers.

    Examples for true answers: SQL injection, XSS, buffer overflow

    In systemd, the actually use OZZ Fuzz. If there's a link to it, add it here.

    Examples for false: RFC violations, permissions issues, anything
    that requires the tool to be "aware" of the project's
    domain-specific requirements.

    The answer field should be boolean. In answer_note, please explain
    why you come to that conclusion.
vcc_instructions: |
  The vulnerability-contributing commits.

  These are found by our tools by traversing the Git Blame history, where we
  determine which commit(s) introduced the functionality.

  Look up these VCC commits and verify that they are not simple refactorings,
  and that they are, in fact introducing the vulnerability into the system.
  Often, introducing the file or function is where the VCC is, but VCCs can be
  anything.

  Place any notes you would like to make in the notes field.
bugs_instructions: |
  What bugs and/or pull requests are involved in this vulnerability?

  For systemd, this is typically their GitHub issues, but could also include
  bugs from other databases. Put a URL instead of a single number.
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.
fixes_instructions: |
  Please put the commit hash in "commit" below.

  This must be a git commit hash from the systemd source repo, a  40-character
  hexademical string/

  Place any notes you would like to make in the notes field.
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: Orignaly at first to be belived as a temp fixed, but actually ended up becoming
      the actual fix
    commit: 156a5fd297b61bce31630d7a52c15614bf784843
  - note: This commit and many others from https://github.com/systemd/systemd/pull/16033  has
      added parse tests
    commit: 707e93aff8f358f8a62117e54b857530d6594e4b
  - note: System patch for systemd for nixpkgs was mentioned within the research
    commit: dbfb40efdd7fed421415620058066bb3e691d735
  - note: The stablized commit version that have same changes applied from 156a5fd297b61bce31630d7a52c15614bf784843
    commit: 6300d6fe54bf02405003babc58f658f7fe712b4d
  question: |
    Are there any interesting commits between your VCC(s) and fix(es)?

    Use this to specify any commits you think are notable in some way, and
    explain why in the note.
order_of_operations:
  note: The fix mainly edited values to be parsed to base 10, no change of code order
  answer: false
  question: |
    Does the fix for the vulnerability involve correcting an order of
    operations?

    This means the fix involves moving code around or changing the order of
    how things are done.

    Answer must be true or false.
    Write a note about how you came to the conclusions you did, regardless of
    what your answer was.
curated_instructions: |
  If you are manually editing this file, then you are "curating" it.

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

  This is not the same as published date in the NVD - that is below.

  Please enter your date in YYYY-MM-DD 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