Cybercriminals identified as “Codefinger” have recently targeted Amazon Web Services (AWS) S3 buckets, encrypting customer data using AWS’s native encryption tools. According to researchers from Halcyon, the attackers use a method known as server-side encryption with customer-provided keys (SSE-C) to lock victims out of their own data. This approach involves stealing AWS account credentials, obtaining the corresponding encryption keys, and encrypting the data, leaving customers unable to access their files unless they pay a ransom. Halcyon documented two such incidents since December 2024, both involving AWS-native software developers as victims, though further details about the attackers’ origin or typical targets remain unclear.
The Codefinger hackers’ method is using AWS’s own encryption tools to encrypt the data:
The Codefinger hackers’ method of using AWS’s own encryption tools to encrypt the data represents a significant advancement in ransomware tactics. Normally, encryption is a tool for securing data, but the attackers’ use of SSE-C creates an encryption that is both secure and unrecoverable without the hackers’ cooperation. Without the decryption keys, victims are unable to recover their data, and there is no known way to bypass the encryption, making this attack particularly severe. In their ransom notes, the hackers warn victims not to alter AWS account permissions, using threats of file deletion within seven days to pressure victims into paying the ransom.
Amazon Web Services has responded to concerns, stating that when the company becomes aware of exposed encryption keys, it notifies affected customers and investigates any potential breaches. AWS encourages its customers to avoid storing credentials in source code or configuration files, a common practice that can expose them to cyberattacks. Although AWS has provided resources for affected customers and is actively investigating these incidents, the overall security of S3 buckets remains a concern due to their common exposure on the internet. Researchers have long warned that misconfigured S3 buckets can lead to massive data breaches, and now ransomware actors have found ways to exploit these vulnerabilities for financial gain.
Halcyon’s researchers also noted that this attack is an evolution of earlier ransomware tactics, where attackers leveraged legitimate encryption services, like Microsoft’s BitLocker, to lock users out of their systems. The growing trend of ransomware groups targeting cloud storage services like AWS further amplifies the risk to organizations using these services. Halcyon urges AWS customers to take immediate action to protect their data from similar attacks, as the new tactics used by Codefinger may soon spread to other threat actors. The continued evolution of ransomware tactics highlights the need for robust cloud security practices and heightened awareness of potential threats to prevent future breaches.
