CVE-2021-43809 (Markdown, published 2021-12-08T19:15Z)
Description: value: `Bundler` is a package for managing application dependencies in Ruby. In `bundler` versions before 2.2.33, when working with untrusted and apparently harmless `Gemfile`'s, it is not expected that they lead to execution of external code, unless that's explicit in the ruby code inside the `Gemfile` itself. However, if the `Gemfile` includes `gem` entries that use the `git` option with invalid, but seemingly harmless, values with a leading dash, this can be false. To handle dependencies that come from a Git repository instead of a registry, Bundler uses various commands, such as `git clone`. These commands are being constructed using user input (e.g. the repository URL). When building the commands, Bundler versions before 2.2.33 correctly avoid Command Injection vulnerabilities by passing an array of arguments instead of a command string. However, there is the possibility that a user input starts with a dash (`-`) and is therefore treated as an optional argument instead of a positional one. This can lead to Code Execution because some of the commands have options that can be leveraged to run arbitrary executables. Since this value comes from the `Gemfile` file, it can contain any character, including a leading dash.

To exploit this vulnerability, an attacker has to craft a directory containing a `Gemfile` file that declares a dependency that is located in a Git repository. This dependency has to have a Git URL in the form of `-u./payload`. This URL will be used to construct a Git clone command but will be interpreted as the upload-pack argument. Then this directory needs to be shared with the victim, who then needs to run a command that evaluates the Gemfile, such as `bundle lock`, inside.

This vulnerability can lead to Arbitrary Code Execution, which could potentially lead to the takeover of the system. However, the exploitability is very low, because it requires a lot of user interaction. Bundler 2.2.33 has patched this problem by inserting `--` as an argument before any positional arguments to those Git commands that were affected by this issue. Regardless of whether users can upgrade or not, they should review any untrustred `Gemfile`'s before running any `bundler` commands that may read them, since they can contain arbitrary ruby code.
Severity: HIGH (CVSS v3 base score: 7.3)
Weakness: CWE-88 \u2014 Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')
The product constructs a string for a command to be executed by a separate component
in another control sphere, but it does not properly delimit the
intended arguments, options, or switches within that command string.
Repository: https://github.com/rubygems/rubygems
Files changed:
bundler/CHANGELOG.md
Commit message: Changelog for Bundler version 2.2.33


Vulnerable code:

Fixed code:
# 2.2.33 (December 7, 2021)

## Security fixes:

  - Pass "--" to git commands to separate positional and optional args [#5142](https://github.com/rubygems/rubygems/pull/5142)

## Enhancements:

  - Accept pull request URLs as github source [#5126](https://github.com/rubygems/rubygems/pull/5126)
  - Add `--version` parameter to `bundle info` command [#5137](https://github.com/rubygems/rubygems/pull/5137)
  - Let original `Errno::EACCES` error be raised in compact index updater [#5110](https://github.com/rubygems/rubygems/pull/5110)
  - Improve gemfile-lockfile source equivalence errors [#5120](https://github.com/rubygems/rubygems/pull/5120)
  - Avoid float-to-string loss of characters in GitHub Actions configuration labels in new gem template [#5089](https://github.com/rubygems/rubygems/pull/5089)
  - Add an initial rbs template to `bundle gem` skeleton [#5041](https://github.com/rubygems/rubygems/pull/5041)
  - Avoid shared libraries not getting environment passed right after argv in memory when `bundle exec` is used [#4815](https://github.com/rubygems/rubygems/pull/4815)

## Bug fixes:

  - Don't cleanup paths from gems already activated from `$LOAD_PATH` [#5111](https://github.com/rubygems/rubygems/pull/5111)
  - Fix handling prereleases of 0 versions, like 0.0.0.dev or 0.0.0.SNAPSHOT [#5116](https://github.com/rubygems/rubygems/pull/5116)
  - Fix escape of filenames in `bundle doctor` [#5102](https://github.com/rubygems/rubygems/pull/5102)
  - Don't unlock dependencies when running `bundle install` after changing global source [#5090](https://github.com/rubygems/rubygems/pull/5090)
  - Fix missing locked specs when depended on another platform [#5092](https://github.com/rubygems/rubygems/pull/5092)
  - Fix `bundle info` sometimes claiming that bundler has been deleted [#5097](https://github.com/rubygems/rubygems/pull/5097)

## Documentation:

  - Ignore to generate the documentation from vendored libraries [#5118](https://github.com/rubygems/rubygems/pull/5118)