CodeBreach: How Two Missing Characters Almost Toppled the AWS Cloud

Security researchers from the cybersecurity firm Wiz have unearthed a critical vulnerability within the AWS CodeBuild service, which facilitated a total takeover of Amazon’s own GitHub repositories and posed a catastrophic risk to cloud environments globally.

Designated as CodeBreach, this flaw was disclosed to Amazon last August and remediated in September, preceding any illicit exploitation. According to researchers, this intervention averted a supply chain offensive that could have potentially eclipsed the infamous SolarWinds breach in magnitude. “This vulnerability compromised a pivotal library utilized within the AWS Console—the central nervous system of the cloud,” explained Wiz researcher Yuval Avrahami to The Register. He underscored that while the SolarWinds incursion granted adversaries access to corporate networks, this breach could have empowered them to execute code directly within the interface through which administrators govern their entire infrastructure.

The genesis of the vulnerability was disconcertingly rudimentary: a mere two characters were omitted from webhook filters. CodeBuild, Amazon’s managed continuous integration service, frequently interfaces with GitHub repositories. To safeguard against untrusted pull requests, specialized filters are employed; specifically, the ACTOR_ID filter allows for a curated list of approved GitHub contributors authorized to trigger builds.

The defect resided in the regular expression governing this filter, which lacked “anchoring”—the symbols denoting the inception and conclusion of a string. In their absence, the system did not demand an exact match for the identifier but merely searched for a substring. Consequently, any GitHub user possessing an ID that encompassed the ID of an approved maintainer could circumvent the defensive perimeter.

The Wiz team devised a method to register the requisite identifier via the GitHub Apps feature, automating the generation of two hundred application registration requests. One attempt proved successful, granting them a trusted ID associated with a maintainer of the AWS SDK for JavaScript. Subsequently, they orchestrated a pull request disguised as a standard remediation for a legitimate issue. Concealed within was a malicious payload—an NPM package dependency engineered to exfiltrate GitHub credentials from the build environment. Within moments, the researchers secured unfettered access to the repository, enabling them to appoint an administrator with the authority to merge code into the primary branch and approve subsequent pull requests.

The potential theater of impact is staggering: Wiz data suggests that Amazon’s JavaScript SDK is integrated into 66% of cloud environments, including the AWS Console itself. An adversary could have surreptitiously injected deleterious code into the SDK immediately prior to a weekly release, thereby infecting the library’s entire user base. Avrahami remarked that such an operation required no extraordinary technical prowess, only the skill level of a median developer; the true complexity lay in camouflaging the malicious intent as an innocuous contribution.

Amazon has asserted that no client environments or corporate services were compromised. The cloud titan remediated the flaw within 48 hours of the initial report, conducted a comprehensive audit of all public build environments, and verified through log analysis that no external entities, aside from Wiz, had exploited the breach. A formal security bulletin regarding the incident has since been published.

Nevertheless, Avrahami cautions that such threats are not unique to AWS. This vulnerability exploits a persistent blind spot in CI/CD pipeline security—a risk shared by all major cloud providers and technology firms utilizing GitHub Actions, Jenkins, or analogous continuous integration systems.