Growing Threat of Amazon S3 Ransomware Attacks

By
Edwin Alexander
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Growing Threat of Amazon S3 Ransomware Attacks

In today’s cloud-first landscape, ransomware is no longer just a desktop or server-side threat. A new wave of cloud-native ransomware is taking aim at Amazon S3, one of AWS’s most widely used storage services. These attacks weaponize AWS’s own infrastructure—specifically, S3 buckets and encryption configurations—to lock organizations out of their data. No malware. No suspicious binaries. Just smart abuse of trusted services.

As observed in a string of high-profile attacks throughout 2023 and early 2025, this emerging threat vector is no longer theoretical. Security researchers, threat intel platforms, and even AWS themselves have acknowledged the rise of this technique, pushing urgent guidance to help organizations defend their cloud assets before it’s too late.

 

🧠 What Is Amazon S3 Ransomware?

Traditional ransomware typically infects endpoints via malicious attachments or exploit kits, encrypting files locally and demanding payment. S3 ransomware flips the script: attackers don’t need to infect a device at all.

Instead, they gain access to a cloud account—usually through stolen credentials, poor IAM configurations, or unmonitored third-party access—and then use native AWS services to encrypt or delete cloud data.

Once inside, attackers exploit the very features designed to secure data—such as server-side encryption with KMS or SSE-C—to take control. Victims are then locked out, facing a painful choice: pay up or lose access to terabytes of critical data.

 

🔥 Real Incidents and Rising Impact

In early 2025, InfoQ reported that multiple AWS customers had fallen victim to ransomware groups exploiting S3 buckets. In one incident, attackers encrypted client databases hosted in S3 and demanded cryptocurrency in exchange for the decryption key. The companies had no malware infections—just mysteriously locked files that even AWS support couldn’t unlock.

A BleepingComputer report further explained how attackers abused server-side encryption settings in S3 to force re-encryption with attacker-controlled keys.

According to Cybernews, this technique has become a favoured tool for financially motivated threat actors and insider threats. Unlike noisy malware, these operations are stealthy, relying solely on privileged access and standard AWS APIs.

 

🔍 In-Depth Breakdown of Attack Techniques

1. 🔑 KMS-Based Encryption Hijack

This is one of the most insidious techniques observed. Here’s how it works:
  • The attacker creates a KMS key in their own account (or in the victim’s if they have full access).
  • They modify the S3 bucket’s encryption configuration to use this new KMS key.
  • Existing objects are re-encrypted using the new key—rendering them inaccessible without the attacker’s cooperation.
  • Victims may still see their data but are blocked from accessing or downloading it.

2. 🧬 SSE-C (Customer-Provided Key) Exploitation

Server-Side Encryption with Customer-Provided Keys (SSE-C) is rarely used in production environments but can be abused in attacks:
  • The attacker generates a random encryption key (not stored by AWS).
  • They re-upload all S3 objects using this key.

Even AWS cannot decrypt these objects without the attacker’s key.

 

🛡️ How to Defend Against S3 Ransomware

The rise of S3-based ransomware calls for cloud-specific defense tactics. Here’s what organizations should prioritize:

1. ✅ Identity and Access Management (IAM) Hygiene

  • Enforce least privilege access policies.
  • Use service control policies (SCPs) to restrict encryption setting changes.
  • Require MFA for high-privilege accounts.

2. 🕵️♂️ Monitor Encryption and API Activity

  • Enable CloudTrail with logging for S3 and KMS events.
  • Use AWS Config rules to alert on encryption setting changes.
  • Monitor for sudden spikes in SSE-C or KMS activity.

3. 💾 Enable S3 Versioning and MFA Delete

  • Versioning ensures that even deleted or overwritten files have recoverable versions.
  • Enable MFA Delete to prevent unauthorized object deletion.

4. 🔄 Isolated Backups and Disaster Recovery

  • Store backups in a separate AWS account with tightly restricted access.
  • Regularly test recovery processes to ensure RTO/RPO objectives are met.

5. 📜 Policy Enforcement

  • Use AWS Organizations + SCPs to block risky operations organization-wide
  • Set S3 bucket policies to deny encryption configuration changes by default.

 

🧠 Final Thoughts

S3 ransomware is a wake-up call: the cloud is not inherently secure. When attackers can weaponize the very tools meant to protect data, defenders must adapt.

What makes these attacks dangerous isn’t just the data loss—it’s the invisibility. Without malware to scan for or anomalies to catch with traditional EDRs, your only line of defense is proactive configuration, monitoring, and least-privilege access.

As ransomware tactics continue evolving, it’s clear that traditional security measures alone are no longer enough—especially in the cloud. Threat actors are now exploiting trusted AWS features to lock down data without ever deploying malware.

If your organization relies on Amazon S3 storage , now is the time to act

🛡️ Don’t wait for a breach to start securing your cloud.
Learn how Exabytes can help you harden your AWS environment with proactive cloud security solutions.

👉Visit Exabytes eSecure to get started.

 

📚 References

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