CodeBreach: Critical AWS CodeBuild Misconfiguration Enabling Supply Chain Repository Takeover

A critical misconfiguration in Amazon Web Services (AWS) CodeBuild could have allowed attackers to gain complete control over GitHub repositories used in AWS CI/CD pipelines, including the widely used AWS JavaScript SDK, introducing a severe software supply chain risk.

This vulnerability, codenamed CodeBreach, stemmed from insufficiently restrictive CI pipeline configurations, build triggers, and webhook filters.

AWS has since remediated the core misconfiguration and implemented hardening protections; however, this incident highlights persistent software supply chain weaknesses that affect CI/CD practices across cloud environments.

What Is CodeBreach?

CodeBreach refers to a critical supply chain misconfiguration vulnerability affecting AWS CodeBuild integration with GitHub repositories. It did not originate from a traditional software bug in CodeBuild itself; rather, the vulnerability was rooted in how CodeBuild’s CI configurations and webhook filters were defined for certain AWS GitHub repositories.

At a high level, the misconfiguration could have allowed an attacker to:

• Bypass repository filtering controls and trigger privileged builds,
• Harvest GitHub credentials (such as Personal Access Tokens) from CodeBuild environments,
• Push unauthorized code changes to core repositories, and
• Potentially inject malicious code into widely consumed software components like the AWS JavaScript SDK.

This combination of capabilities forms a classic software supply chain attack vector, where attackers leverage configuration weaknesses in trusted infrastructure to distribute malicious software to downstream users.

CodeBreach – Technical Root Cause

The root cause of CodeBreach was overly permissive and improperly constructed filters and CI/CD configurations. Specifically:

1. Misconfigured Webhook Filters:
   AWS CodeBuild uses GitHub webhooks to detect repository events (e.g., pushes, pull requests) and trigger builds. In several AWS-managed repositories, webhook filter patterns intended to allow only trusted actor IDs lacked proper anchoring (^ and $), permitting unauthorized users whose numeric IDs included the trusted IDs as substrings to trigger builds.
2. Insufficient Restriction of Build Triggers:
   Because CI triggers were not tightly scoped to intended actors or events, it became possible to initiate builds in contexts that should have been blocked, thereby activating the vulnerable pipeline logic.
3. Credential Exposure in Build Environments:
   When a build runs, CodeBuild environments can contain GitHub authentication tokens needed to interact with the repository. An attacker who can trigger a privileged build may extract those tokens from memory, and then use them to perform write actions on the repository.

Together, these vulnerabilities created a scenario where an attacker could authorize a build that granted them elevated repository access without appropriate restrictions.

Exploitation Path: How CodeBreach Could Lead to Repository Takeover

Below is a step-by-step outline of how an exploit of CodeBreach might unfold:

Initial Trigger via Webhook Bypass

An attacker constructs GitHub actor IDs that match the misconfigured webhook filters due to missing anchors. This allows them to bypass the intended filtering logic and trigger the CI build process for the target repository.

Build Execution and Token Exposure

Once the unauthorized build is triggered, the attacker can:

• Execute actions within the CodeBuild environment,
• Dump memory to extract sensitive credentials such as GitHub access tokens used by the build process.

Repository Compromise

Using extracted tokens, the attacker gains administrative repository access and can:

• Force push malicious changes,
• Merge unauthorized pull requests,
• Inject backdoors into code components, including components used in millions of applications.

Supply Chain Distribution

Compromised code could be published or consumed by downstream projects, triggering a cascading supply chain compromise across ecosystems that depend on the affected repositories.

Note: AWS reported that no evidence of exploitation in the wild was observed following remediation.

CodeBreach – Mitigation and Remediation Guidance

Although the vulnerability was fixed by AWS within a short period of responsible disclosure, organizations should apply the following best practices to protect their own CI/CD pipelines and supply chain automation workflows:

Webhook and Filter Hardening

• Always anchor regex filters (^…$) used for event and actor validation to ensure precise matches.
• Validate webhook payloads strictly against expected event types and actor identities.

Least Privilege for CI/CD Tokens

• Use fine-grained GitHub App tokens or scoped PATs with only necessary permissions.
• Rotate and expire tokens regularly.
• Do not embed long-lived credentials in build environments.

Build Trigger Controls

• Require explicit approvals or gated workflows for builds that can alter production or core repositories.
• Where available, enable build gate features (e.g., Pull Request Comment Approval) instead of relying solely on automated webhook triggers.

CI/CD Pipeline Auditing

• Monitor CI/CD logs for anomalous build triggers.
• Track which identities have invoked builds and alert on unexpected patterns.

Repository Protection Policies

• Enforce protected branch rules and code review requirements to block pushes from unauthorized sources, even if tokens are compromised.

How AppTrana WAAP Helps Detect and Prevent Supply Chain Abuse

AppTrana WAAP provides layered protection that helps mitigate risks like CodeBreach by:

• Detecting and blocking malicious inbound webhook requests that deviate from intended usage patterns,
• Applying intent-based inspection to identify unauthorized CI/CD trigger attempts,
• Limiting exposure during patch windows by filtering malicious commands or exploitation attempts.

By combining behavioral analysis with signature and context-aware detection, AppTrana adds an enforcement layer that catches suspicious build triggers before they can activate dangerous workflows.

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