Description

A fail-open error handling issue within the data masking utility of Powertools for AWS Lambda (Python) might allow actors to read sensitive field values that the application intended to mask.  To remediate this issue, users should upgrade to version 3.35.0.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "5.3",
  "pubDate": "2026-10-01T22:17:00.567Z",
  "pubdate": "2026-10-01T22:17:00.567Z",
  "executiveSummary": "A critical fail-open vulnerability exists within the data masking utility of Powertools for AWS Lambda (Python).\nThis vulnerability is classified as an improper error handling flaw, specifically manifesting as a fail-open security state during the data transformation process.\nThe primary impact is the unauthorized exposure of sensitive information that was explicitly intended to be obfuscated or redacted by the masking utility.\nIf the masking logic encounters an error during execution, the component fails to sanitize the output, inadvertently returning the raw, unmasked data to the calling function or downstream log/sink.\nThis represents a significant security risk for applications processing Personally Identifiable Information (PII) or other sensitive payloads.\nAn attacker capable of triggering error states within the data processing pipeline—perhaps through malformed inputs or specifically crafted payloads—can effectively bypass intended data loss prevention (DLP) controls.\nBecause the system defaults to allowing the original data through rather than enforcing a secure fallback (such as blocking the output or returning a null/error value), sensitive data is exposed in plain text within application logs, metrics, or API responses.\nThe vulnerability affects versions prior to 3.35.0 of the Powertools for AWS Lambda (Python) library.",
  "technicalDetails": "The vulnerability resides within the data masking utility of the Powertools for AWS Lambda (Python) framework. The flaw is rooted in how the utility manages exceptions during the masking transformation process. In a secure implementation, masking operations should follow a 'fail-closed' or 'deny-by-default' architecture, where any exception during processing causes the system to either block the output entirely or redact it completely to ensure no sensitive information is leaked.\nIn this implementation, the error handling logic is configured to 'fail-open.' When the masking function encounters an unexpected input format, a schema mismatch, or a processing exception, the utility does not catch the failure in a way that prevents the underlying sensitive data from being returned. Instead, the function returns the raw input value, bypassing the intended security controls.\nThe exploitation flow typically involves an attacker providing inputs that cause the masking utility to fail. By injecting unconventional characters, unexpected data types, or payloads that exceed defined structural constraints, the attacker forces the utility to drop into an error state. Because the underlying logic fails to intercept this state, the 'masked' variable is populated with the raw input string instead of the desired obfuscated string.\nThis behavior results in sensitive data, which should have been restricted, being passed through the application logic. If this data is subsequently logged, sent to cloud-native monitoring tools, or transmitted via an API, the attacker gains unauthorized access to fields that were intended to be protected by the library's privacy controls.\nThe vulnerability is present in versions of Powertools for AWS Lambda (Python) prior to 3.35.0. It does not require specific authentication or high-level privileges to trigger, provided the attacker can influence the input data that is subjected to the masking process. The network exposure is determined by the accessibility of the Lambda function's input source, such as an API Gateway endpoint or a triggered SQS queue. The post-exploitation impact is the compromise of data confidentiality, potentially leading to regulatory compliance failures and unauthorized disclosure of PII/credentials."
}