Simon Willison’s Weblog

How We Executed a Critical Supply Chain Attack on PyTorch (via) Report on a now handled supply chain attack reported against PyTorch which took advantage of GitHub Actions, stealing credentials from some self-hosted task runners.

The researchers first submitted a typo fix to the PyTorch repo, which gave them status as a “contributor” to that repo and meant that their future pull requests would have workflows executed without needing manual approval.

Their mitigation suggestion is to switch the option from ’Require approval for first-time contributors’ to ‘Require approval for all outside collaborators’.

I think GitHub could help protect against this kind of attack by making it more obvious when you approve a PR to run workflows in a way that grants that contributor future access rights. I’d like a “approve this time only” button separate from “approve this run and allow future runs from user X”. # 14th January 2024, 7:38 pm

Behind GitHub’s new authentication token formats (via) This is a really smart design. GitHub’s new tokens use a type prefix of “ghp_” or “gho_” or a few others depending on the type of token, to help support mechanisms that scan for accidental token publication. A further twist is that the last six characters of the tokens are a checksum, which means token scanners can reliably distinguish a real token from a coincidental string without needing to check back with the GitHub database. “One other neat thing about _ is it will reliably select the whole token when you double click on it”—what a useful detail! # 5th April 2021, 9:28 pm

How we found and fixed a rare race condition in our session handling. GitHub had a terrifying bug this month where a user reported suddenly being signed in as another user. This is a particularly great example of a security incident report, explaining how GitHub identified the underlying bug, what caused it and the steps they are taking to ensure bugs like that never happen in the future. The root cause was a convoluted sequence of events which could cause a Ruby Hash to be accidentally shared between two requests, caused as a result of a new background thread that was introduced as a performance optimization. # 18th March 2021, 11:06 pm

Building a stateless API proxy (via) This is a really clever idea. The GitHub API is infuriatingly coarsely grained with its permissions: you often end up having to create a token with way more permissions than you actually need for your project. Thea Flowers proposes running your own proxy in front of their API that adds more finely grained permissions, based on custom encrypted proxy API tokens that use JWT to encode the original API key along with the permissions you want to grant to that particular token (as a list of regular expressions matching paths on the underlying API). # 30th May 2019, 4:28 am

GitHub: Weak cryptographic standards removal notice. GitHub deprecated TLSv1 and TLSv1.1 yesterday. I like how they handled the deprecation: they disabled the protocols for one hour on February 8th in order to (hopefully) warm people by triggering errors in automated processes, then disabled them completely a couple of weeks later. # 23rd February 2018, 3:41 pm

Introducing security alerts on GitHub. This is huge: GitHub’s dependency graph feature now shows any dependencies that have a known security vulnerability, based on CVE IDs—and you can sign up for notifications of new vulnerabilities as well. Only supports Ruby and JavaScript today, but Python support is coming in 2018. # 16th November 2017, 7:48 pm