Earlier this month, a vulnerability in rubygems.org has been brought to the attention of the Ruby community. The website serves as the central hub for hosting and distributing gems (libraries) used by Ruby developers across the world. The vulnerability, identified as CVE-2023-40165, exposed a potential risk for malicious actors to replace legitimate gem versions on the platform, which may have lead to significant security issues.

Exploit Details

The vulnerability stems from insufficient input validation on rubygems.org. This security lapse enabled potential hackers to replace any uploaded gem version that matched certain criteria (platform, version number, or gem name matching /-\d/). Upon replacing a legitimate gem, an immediate CDN purge would be triggered, which means the malicious gem would be served to users right away.

Fortunately, the maintainers of rubygems.org have thoroughly reviewed the issue and confirmed that no unexpected .gem files were found, suggesting that the vulnerability was never exploited in the wild.

Mitigations and Recommendations

To ensure your application was not impacted by this vulnerability, it is highly recommended that you verify the checksums of your downloaded .gem files. These checksums should match the ones recorded in the RubyGems.org database.

One way to achieve this is to use a tool developed by RubyGems contributor Maciej Mensfeld. To use the tool, simply run the following commands:

bundle add bundler-integrity
bundle exec bundler-integrity

Do note that these tools cannot guarantee that your application was not exploited, but they can provide a quick and effective means of comparing the API-provided checksums with the files stored on your local machine.


The CVE-2023-40165 vulnerability has been promptly addressed by the rubygems.org maintainers, ensuring that the platform remains a reliable and secure environment for the Ruby community. They have implemented improved input validation measures to mitigate this issue, and no further user action is required other than validating your local gems as a precautionary measure.

For more information on the original references, please visit

- RubyGems: Vulnerability Disclosure
- Maciej Mensfeld: Bundler Integrity Tool


Published on: 08/17/2023 18:15:00 UTC
Last modified on: 08/24/2023 20:50:00 UTC