Patching the Polyfill Supply Chain Attack

June 28, 2024

Explore our latest blog post to learn about the recent supply chain attack that has affected over 100,000 websites and how Patchwork, alongside tools like Semgrep, can help you quickly patch your code.

Update on 29th June 2024

It is now believed that the attack was more widespread. It also affects the following domains -,,,,,,,

The original rule published by the Semgrep team doesn't detect these, you can use the updated version we have made available here. We have also updated the config and prompt for the Fixpolyfill patchflow so that it can help remediate this issue in your code.

You can use the updated rule as follows:

patchwork AutoFix semgrep_extra_args='--config r/KxUvD7w/asankhaya_personal_org.polyfill-compromise-copy' 

Polyfill Supply Chain Attack

Semgrep has released a new rule on their blog that can help detect the use of polyfill in your code. Along with semgrep, we can use our open-source solution patchwork to fix the use of polyfill by either removing it fully from code or replacing it with a new implementation from cloudflare.

We already have an AutoFix patchflow that works quite well to fix vulnerabilities in the code. We can pass the new rule as an extra argument to the patchflow to detect this particular issue as follows:

patchwork AutoFix semgrep_extra_args='--config r/3qUkGp2/semgrep.polyfill-compromise'

This will detect the fix and automatically generate a pull request that fixes it. You can see an example run here.

The patchwork framework is very easy to extend and customize. To enable users to handle this particular case well we have created this custom patchflow called Fixpolyfill. With the custom patchflow you can just run:

patchwork Fixpolyfill --config=../patchwork-configs/patchflows

This makes it a lot easier to run the patchflow as the required config is already present in the config.yml file here. We have also modified the default AutoFix prompt to be more specific for this particular issue. With just config and prompt changes one can make a simple reciepe from a patchflow that can be reused across different repos to detect and fix the polyfill issue.

To make it easy to run the patchflow across your entire GitHub (or GitLab) org we have added a couple of options, if you run with the github_org_name, the patchflow will run across all the repos that your GitHub token has access to and generate a summary at the end as follows:

patchwork Fixpolyfill --config=../patchwork-configs/patchflows github_org_name=codelion
'codelion' is a user account, not an organization. Processing repositories.
Processing AltoroJ-Workshop...
Cloning into 'AltoroJ-Workshop'...
remote: Enumerating objects: 691, done.
remote: Counting objects: 100% (98/98), done.
remote: Compressing objects: 100% (46/46), done.
remote: Total 691 (delta 74), reused 53 (delta 52), pack-reused 593
Receiving objects: 100% (691/691), 4.57 MiB | 15.71 MiB/s, done.
Resolving deltas: 100% (290/290), done.
Finished AutoFix: 100%|████████████████████████████████████| 100/100 [00:03<00:00, 25.1it/s]
Processing analyze-aws-lambda...
Cloning into 'analyze-aws-lambda'...

Summary of processed repositories:
| Repository                    | PR URL                                              |
| AltoroJ-Workshop              |                                                     |
| analyze-aws-lambda            |                                                     |
| ASDL2017                      |                                                     |
| AutoBot                       |                                                     |
| ...                           |                                                     |
| example-python                |  |
| faststream                    |                                                     |
| ...                           |                                                     |

Preventing such attacks is incredibly difficult, and the open-source industry is grappling with how best to prevent them. That said, every team has the responsibility to respond swiftly to such events to minimize damage. To that effect, we hope this post has been useful.

If you have any questions or need any help, please feel to write to us at or join the discussion on our discord channel.Recently, there has been a supply chain attack on the CDN service, that was delivering malicious JavaScript code. Sansec discovered that a malicious actor took control of the domain and used to deliver malware to over 100k website that relied on the CDN service.

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