CVE-2017-9805

aka overtrusting xml handler

CVE: CVE-2017-9805
CWE: 502
bugs: []
vccs:
- note: Moved Rest plugin into trunk
  commit: 6229ad7a4726717bf594e9b4e4afa90e1e028829
- note: 
  commit: 
fixes:
- note: Update xstream lib Struts 2.3.X
  commit: 677ccebe83d159d7c0a2274af703a7cc752a04b3
- note: Adds new methods and marks current as deprecated 2.3.X
  commit: 287e3bc8cbd66fdda04b075bc96362bfd3e2dce9
- note: Adds abstract layer to handle API change 2.3.X
  commit: 2776b34b44808f2a4ce2c6fee3c2f3a586bc55b0
- note: Updates flow to handle new API 2.3.X
  commit: 103e3b174e497bbe7058919f12b9f48a0ddf6de3
- note: Defines allowed classes per action 2.3.X
  commit: 6dd6e5cfb7b5e020abffe7e8091bd63fe97c10af
- note: Update xstream lib Struts 2.5.X
  commit: 8216ec1c4d2d1f558558b2464bbcdcd1efe86bc7
- note: Adds new methods and marks current as deprecated 2.5.X
  commit: 2f690cfe6260ccdf3aa617baf65a4b836c49cf65
- note: Adds abstract layer to handle API change 2.5.X
  commit: 3bd072ca053aed787f3a16865266d8832fcd18b0
- note: Updates flow to handle new API 2.5.X
  commit: a64da53d5770c5404ee5eb390b826f5733171f5f
- note: Defines allowed classes per action 2.5.X
  commit: 19494718865f2fb7da5ea363de3822f87fbda264
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: |
      The potentially malicious input is serialzed XML. Because this input isn't
      validated, it can be used to execute arbitrary code during the
      deserialization process.
    applies: true
  complex_inputs:
    note: |
      Because it is deserializing XML, there is potentially a lot of complex
      data that is used to construct Java objects. There is no one parameter
      or input that must be checked but an arbitrary composition of them,
      greatly complicating the input.
    applies: true
  distrust_input:
    note: |
      The input was implicitly being trusted by the deserialization code. This
      means it wasn't sanitizing the input in any way, which would've prevented
      this vulnerability.
    applies: true
  least_privilege:
    note: 
    applies: false
  native_wrappers:
    note: 
    applies: false
  defense_in_depth:
    note: 
    applies: false
  secure_by_default:
    note: 
    applies: false
  environment_variables:
    note: 
    applies: false
  security_by_obscurity:
    note: 
    applies: false
  frameworks_are_optional:
    note: 
    applies: false
upvotes: 3
mistakes:
  answer: |
    This vulnerability was mostly a design mistake. The developer
    did not consider that the input could potentially be malicious and could be
    dangerous when deserialized. As such, the XML handler did not properly
    validate the input before the deserialization occurs, leading to the
    potential execution of arbitrary code. The page for CWE-502 suggests
    validating the input before creating a new object to store the deserialized
    data. The fix for this vulnerability involved 1) upgrading the dependancy
    used for XML deserializing but 2) creating a whitelist of allowed class
    names. This whitelist validates that the input is trustworthy before
    creating the object. If the class instance attempting to be created isn't
    on that list of trusted class names, it is not created. It is interesting
    how this vulnerability was found (a demonstration of a security service that
    automatically queries open-source repositories for security vulnerabilities)
    and that it was very quickly fixed. They also didn't annouce the
    vulnerability before it was fixed, and there were no public bug reports or
    anything to signify that it existed. They were also missing security tests
    that could've prevented this vulnerability from occuring in the first place.
  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 in the software
    engineering industry would find interesting.
nickname: overtrusting xml handler
reported: '2017-09-05'
announced: '2017-09-05'
subsystem:
  name:
  - plugins
  - rest
  answer: |
    The vulnerability was in the XML deserialization handling in the REST API
    plugin for struts. Path to rest plugin is "struts/plugins/rest", path to
    handlers is "struts/plugins/rest/src/main/java/org/apache/struts2/rest/handler/"
  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: '2017-07-17'
  answer: |
    The vulnerability was discovered by someone name Man Yue Mo who works for a
    company called Semmle using their LGTM service. They used a custom query
    that ran an automated search of the Apache Struts repository and reported
    back the potential vulnerability. There is a detailed description of how
    exactly this was done here: https://lgtm.com/blog/apache_struts_CVE-2017-9805
  apache: 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 Apache
    employee (you can tell from their email address). If it's clear that the
    vulnerability was discovered by a contest, fill in the name there.
    The "automated" flag can be true, false, or nil.
    The "apache" 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: |
  CVE-2017-9805 is a security vulnerability that could allow the execution of
  arbitrary code when XML is read into the system. When the vulnerable module
  received an XML payload, it does not properly validate it. This means that it
  could receive a malicious payload that could execute arbitrary code.
unit_tested:
  fix: false
  code: false
  answer: |
    There were no unit tests involved in this vulnerability. There are unit
    tests for XML (de)serialization but the two test files found don't cover
    security risks, just that the hardcoded inputs serialize and deserialize
    properly.
  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?
    Write the reasoning behind your answer in the "answer" field.
    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. Must be just "true" or "false".
    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.
    Must be just "true" or "false".
future_fixes:
- note: 
  commit: 
curation_level: 1
previous_fixes:
- note: 
  commit: 
- note: 
  commit: 
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!)
security_bulletin: S2-052
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: 
  - 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: |
  Students: when initially writing this, ignore this upvotes number.
  Once this work is being reviewed, 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: |
  Nickname is optional. Provide a useful, professional, and catchy nickname for
  this vulnerability. Ideally fewer than 30 characters. This will be shown
  alongside its CVE to make it more easily distinguished from the rest.
reported_instructions: |
  Was there a date that this vulnerability was reported to the team? You can
  find this in changelogs, blogs, bug reports, or perhaps the CVE data.
  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 data.
  Please enter your date in YYYY-MM-DD format.
fixes_vcc_instructions: |
  Please put the SVN commit number in "commit" below, and any notes about how this
  was discovered in the "note" field.
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 Struts-specific
  stuff. Remove references to versions, specific filenames, and other jargon
  that outsiders to Struts would not understand. Technology like "regular
  expressions" is fine, and security phrases like "invalid write" are fine to
  keep too.
incomplete_fix_instructions: |
  Did the above "fixes" actually fix the vulnerability?
  Please list any fixes for the same issue before and after
  this CVE below.