CVE-2025-14764 identifies a cryptographic vulnerability in the Amazon S3 Encryption Client for Go, an open-source client-side encryption library designed to securely write and read encrypted data to Amazon S3 buckets. The core issue stems from the absence of cryptographic key commitment, a mechanism that binds the encrypted data key (EDK) to the ciphertext to prevent substitution attacks. Specifically, when the encrypted data key is stored in an "instruction file" rather than the default S3 metadata record, an attacker with write access to the S3 bucket can replace the EDK with a malicious one that decrypts to different plaintext. This manipulation undermines data integrity by enabling unauthorized alteration of encrypted data without detection. The vulnerability does not compromise confidentiality directly, as the attacker cannot decrypt data without the proper keys, nor does it affect availability. However, the integrity breach can have serious consequences for applications relying on the authenticity of encrypted data. Exploitation requires network access and low privileges (write access to the bucket) but no user interaction, making it feasible in environments with insufficient access controls. AWS has remediated this vulnerability in version 4.0.0 of the S3 Encryption Client for Go by introducing proper cryptographic key commitment. No known exploits are currently reported in the wild. Organizations using this client library for encrypting data in S3 should prioritize upgrading to the fixed version and review their bucket access policies to prevent unauthorized write access. This vulnerability is classified under CWE-327 (Use of a Broken or Risky Cryptographic Algorithm) and carries a CVSS v3.1 score of 5.3, reflecting a medium severity rating.

For European organizations, this vulnerability poses a significant risk to data integrity in cloud storage environments utilizing the Amazon S3 Encryption Client for Go. Organizations that rely on client-side encryption to protect sensitive or regulated data could face undetected data tampering if an attacker gains write access to their S3 buckets. This could affect sectors such as finance, healthcare, and government, where data integrity is paramount. While confidentiality and availability are not directly impacted, the ability to alter encrypted data without detection can lead to erroneous business decisions, compliance violations (e.g., GDPR mandates on data integrity), and reputational damage. The requirement for write access to the bucket means that misconfigured permissions or insider threats are primary risk vectors. The medium CVSS score reflects moderate exploitability and impact, but the scope can be broad given the widespread use of AWS services in Europe. Organizations with automated workflows or critical data pipelines depending on encrypted S3 objects are particularly vulnerable to silent data corruption or injection of malicious data payloads.

1. Upgrade the Amazon S3 Encryption Client for Go to version 4.0.0 or later immediately to ensure the cryptographic key commitment is enforced and the vulnerability is patched. 2. Conduct a thorough audit of S3 bucket policies and IAM roles to restrict write access strictly to trusted users and services, minimizing the risk of unauthorized EDK substitution. 3. Implement monitoring and alerting on S3 bucket write operations, especially focusing on changes to instruction files or encrypted data keys, to detect suspicious activity promptly. 4. Use AWS CloudTrail and S3 access logs to track and investigate anomalous write events. 5. Where possible, enforce encryption metadata storage within S3 object metadata rather than instruction files to reduce exposure. 6. Review and enhance key management practices, including rotation and validation of encrypted data keys, to detect inconsistencies. 7. Educate development and DevOps teams about the importance of using updated cryptographic libraries and secure coding practices to prevent similar vulnerabilities. 8. Consider implementing additional integrity verification mechanisms at the application layer to detect unauthorized data modifications.