Executive Summary

On January 15, 2026, security firm Wiz disclosed CodeBreach, a critical vulnerability in Amazon Web Services' AWS CodeBuild service. The flaw, now patched, could have allowed unauthenticated attackers to gain administrative access to connected GitHub repositories by bypassing misconfigured webhook filters. The primary risk was a potential supply chain attack against core software libraries, most notably the AWS JavaScript SDK, which is used in a majority of cloud environments and within the AWS Console itself. A successful exploit could have led to the widespread distribution of malicious code, compromising countless downstream users and cloud infrastructures. AWS confirmed the flaw was fixed promptly after responsible disclosure in August 2025 and stated that no customer environments were impacted.

Threat Overview

The CodeBreach vulnerability was a high-impact misconfiguration within the AWS CodeBuild CI/CD service. It allowed an attacker to bypass the intended security controls that trigger build jobs from GitHub events. The core of the issue was a faulty regular expression in a webhook filter that failed to properly validate the source of a build trigger. An unauthenticated attacker, knowing the actor ID of a legitimate GitHub account associated with a target repository, could craft a malicious request to initiate a build.

Once the build was triggered, the attacker could exploit the environment to leak the highly privileged GitHub Personal Access Token (PAT) associated with the CodeBuild project. In the case of the AWS JavaScript SDK repository, this token had full administrative privileges, enabling the attacker to:

1. Push malicious code directly to the main branch.
2. Approve their own malicious pull requests.
3. Modify repository settings and secrets.

The discovery was prompted by a real-world, albeit failed, supply chain attack attempt against the Amazon Q VS Code extension, which used a similarly vulnerable CodeBuild project. This incident underscores the growing trend of attackers targeting CI/CD pipelines as a vector for broad-impact supply chain compromises.

Technical Analysis

The attack chain relied on exploiting a logic flaw in the webhook filtering mechanism of AWS CodeBuild.

1. Initial Access - Bypassing Webhook Filters: The attacker crafts a git-upload-pack request that includes a specific GitHub actor ID in the payload. The misconfigured regex on the AWS CodeBuild webhook listener failed to properly anchor its checks, allowing this crafted request to be processed as a legitimate trigger. This maps to T1190 - Exploit Public-Facing Application.

2. Execution - Triggering a Malicious Build: The malicious request successfully triggers a new build job within the victim's CodeBuild environment. The attacker can specify a buildspec that contains commands to exfiltrate secrets.

3. Credential Access - Leaking GitHub Token: Inside the compromised build environment, the attacker's commands can access environment variables or configuration files containing the GitHub PAT. This token is then exfiltrated to an attacker-controlled server. This aligns with T1552.006 - Group Policy Preferences where secrets are stored in accessible locations.

4. Impact & Persistence - Code Repository Compromise: With the administrative PAT, the attacker gains full control over the target GitHub repository. They can inject malicious code, creating a backdoor in a trusted software library. This constitutes a classic T1195.001 - Compromise Software Dependencies and Development Tools supply chain attack. The ability to approve pull requests and modify code also provides a form of persistence within the development lifecycle.

MITRE ATT&CK Mapping

Impact Assessment

A successful exploitation of CodeBreach would have been catastrophic. The primary target identified, the AWS JavaScript SDK, is a foundational component for a vast number of applications and services that interact with AWS. According to Wiz, 66% of cloud environments utilize this SDK.

• Widespread Compromise: Injecting malicious code into an official release of the SDK would have resulted in a massive supply chain attack, distributing malware to potentially millions of downstream systems and applications globally.
• Compromise of AWS Console: Since the AWS Console itself uses this SDK, attackers could have potentially gained code execution capabilities within the primary management interface for all AWS services, giving them a foothold to attack customer environments from a trusted source.
• Loss of Trust: Such a breach would have severely damaged trust in AWS's software distribution and the security of its core services.
• Financial and Reputational Damage: The fallout for AWS and its customers would have been immense, involving costly incident response, remediation efforts, and significant reputational harm.

Cyber Observables for Detection

Security teams should hunt for signs of CI/CD pipeline abuse:

Detection & Response

Detecting this type of attack requires deep visibility into CI/CD pipeline activity and repository interactions.

• Log Analysis (D3-NTA): Implement Network Traffic Analysis on egress traffic from build environments. Baseline normal traffic patterns and alert on connections to unusual destinations or large data transfers. Ingest AWS CloudTrail and CodeBuild execution logs into a SIEM.
• Behavioral Analysis (D3-UBA): Use User Behavior Analysis on service accounts and CI/CD roles. Alert on anomalous activities, such as a CodeBuild role accessing unusual secrets or a GitHub service account approving PRs outside of normal working hours.
• Configuration Auditing: Regularly audit CodeBuild project configurations, especially webhook filters and permissions. Use automated tools to detect overly permissive regex or missing authentication checks.
• Incident Response Playbook: Develop a specific playbook for a suspected CI/CD pipeline compromise. Key steps should include immediately revoking the associated GitHub token, isolating the build environment, analyzing build logs for exfiltrated data, and scanning all recent code commits for malicious changes.

Mitigation

While AWS has patched the specific flaw, organizations should adopt a defense-in-depth strategy for their CI/CD pipelines.

1. Principle of Least Privilege (M1026): Ensure CodeBuild projects and their associated service accounts have the minimum permissions necessary. GitHub tokens should be scoped to specific repositories and granted only the required access (e.g., read-only if pushes are not needed). This maps to D3-UAP: User Account Permissions.

2. Harden Webhook Configurations (M1054): Implement strict validation on all incoming webhooks. Use cryptographic verification (e.g., webhook secrets) to ensure triggers originate from a trusted source, rather than relying solely on IP filtering or payload inspection. This is a form of Application Configuration Hardening (D3-ACH).

3. Audit and Monitor (M1047): Continuously monitor CI/CD logs (CloudTrail, CodeBuild logs) and source code repository audit logs (GitHub audit logs) for suspicious activity. Set up alerts for events like direct pushes to protected branches or changes in repository permissions by automated accounts. This relates to Domain Account Monitoring (D3-DAM).

4. Require Pull Request Reviews: Enforce policies that require human review for all pull requests, even those from automated systems. Do not allow CI/CD service accounts to merge code into protected branches without oversight.