Silent Strings: How a Two-Character Flaw Nearly Poisoned the AWS Supply Chain

The cloud’s trusted backbone was nearly compromised by a flaw so minute it hid in plain sight: two missing characters in a regular expression. In a chilling echo of recent supply chain attacks, hackers discovered a way to hijack AWS’s core JavaScript SDK, opening the door to backdooring the very tools that power the global cloud.

The Anatomy of an Invisible Threat

It began with a researcher’s sharp eye for the invisible: AWS’s CodeBuild pipelines, responsible for building and releasing the JavaScript SDK, had a subtle vulnerability. Their webhook filters, meant to block untrusted pull requests, relied on regular expressions to check GitHub user IDs against an allow list. But these regex patterns lacked start (^) and end ($) anchors. The result? Any attacker could create a GitHub account whose ID contained a trusted maintainer’s ID as a substring, and slip undetected through the filter.

Leveraging GitHub’s sequential ID assignment, attackers automated the creation of bot accounts, hunting for the right ID combination. Once achieved, they submitted a malicious pull request to the aws-sdk-js-v3 repository. The poisoned PR triggered a build, giving attackers access to the process memory - where privileged GitHub credentials lay unguarded.

With these credentials, hackers could have seized complete control of the JavaScript SDK repository and related private repos. The potential for disaster was immense: malicious code injected directly into AWS’s core SDK, backdoors distributed to millions of applications, and the AWS Console itself compromised from within. At least three other AWS repositories were vulnerable, with automation and even employee accounts at risk.

Lessons from the Edge

The attack surfaced just months after a similar compromise of the Amazon Q VS Code extension, also traced to CodeBuild misconfigurations. In both cases, the flaws were subtle - overlooked in the race for automation, yet powerful enough to threaten the entire cloud ecosystem.

AWS moved quickly after responsible disclosure, patching the vulnerabilities and rolling out new security measures. Manual PR approval gates now stand guard, and all CodeBuild users are urged to anchor their regex filters and minimize access privileges. While no evidence suggests downstream users were affected, the incident underscores a stark lesson: in the world of supply chain security, the smallest oversight can have global consequences.

WIKICROOK

• Regular Expression (Regex): A regular expression (regex) is a pattern used to search, match, or manipulate text. Misused regex can cause security vulnerabilities.
• CI/CD Pipeline: A CI/CD pipeline automates code testing and deployment, enabling developers to deliver software updates quickly, reliably, and with fewer errors.
• Webhook: A webhook is a way for software to instantly send data or alerts to another application’s web address when specific events happen.
• Pull Request (PR): A pull request (PR) allows developers to propose and review code changes before merging into the main project, improving security and quality.
• Supply Chain Attack: A supply chain attack is a cyberattack that compromises trusted software or hardware providers, spreading malware or vulnerabilities to many organizations at once.