CVE-2025-23206 identifies a vulnerability in the AWS Cloud Development Kit (AWS CDK), specifically within the IAM OIDC custom resource provider package. The vulnerability stems from the use of Node.js's tls.connect method with the rejectUnauthorized option set to false by default. This setting disables TLS certificate validation, allowing the client to accept connections from OIDC providers with invalid or untrusted certificates. This improper verification of cryptographic signatures (CWE-347) can potentially expose applications to man-in-the-middle (MITM) attacks during the retrieval of CA thumbprints as part of the custom resource workflow. However, the risk is somewhat mitigated because this code executes within an AWS Lambda environment, which limits exposure. The AWS CDK team recognizes that enforcing rejectUnauthorized: true by default could break existing applications relying on connections to unauthorized OIDC providers. To address this, a feature flag '@aws-cdk/aws-iam:oidcRejectUnauthorizedConnections' will be introduced in CDK version 2.177.0, allowing users to opt-in to strict TLS verification. Until the patch is released, users are advised to upgrade to version 2.177.0 upon availability and enable the feature flag in their cdk.context.json or cdk.json configuration files. There are no known workarounds, and no exploits have been reported in the wild. The vulnerability has a CVSS 4.0 base score of 1.8, reflecting its low severity due to the requirement of high privileges, user interaction, and the mitigating Lambda environment.

For European organizations, the impact of CVE-2025-23206 is limited but non-negligible. Organizations using AWS CDK versions prior to 2.177.0 with IAM OIDC custom resource providers that connect to untrusted or unauthorized OIDC endpoints may be exposed to man-in-the-middle attacks during the CA thumbprint download process. This could lead to the injection of malicious data or interception of sensitive information during infrastructure provisioning workflows. However, the Lambda execution environment reduces the attack surface, and exploitation requires high privileges and user interaction, limiting the likelihood of widespread impact. Nonetheless, organizations relying heavily on automated cloud infrastructure provisioning with AWS CDK should consider this vulnerability seriously, as it could undermine the integrity of their infrastructure as code deployments. Failure to patch could result in subtle security compromises, especially in environments where OIDC providers are externally managed or less trusted. The low CVSS score reflects the limited scope and difficulty of exploitation, but the potential impact on confidentiality and integrity in critical cloud infrastructure provisioning workflows warrants prompt remediation.

European organizations should plan to upgrade their AWS CDK installations to version 2.177.0 or later as soon as it becomes available (expected February 22, 2025). After upgrading, they must explicitly enable the feature flag '@aws-cdk/aws-iam:oidcRejectUnauthorizedConnections' in their cdk.context.json or cdk.json configuration files to enforce strict TLS certificate validation during OIDC custom resource workflows. This approach balances security with backward compatibility. Organizations should audit their CDK applications to identify any reliance on unauthorized or self-signed OIDC providers and assess the risk of enabling strict TLS verification. Where possible, replace untrusted OIDC providers with properly certified endpoints. Additionally, implement monitoring and alerting on Lambda execution environments for unusual network activity that could indicate attempted MITM attacks. Since no workarounds exist, prioritizing the upgrade and configuration change is critical. Finally, incorporate this vulnerability into cloud infrastructure security assessments and DevSecOps pipelines to ensure ongoing compliance.