# Azure Blob Storage Ransomware: Four Storage-Encryption Abuse Methods (BlackCat/ALPHV, STORM-0501)

> Threat actors abuse native Azure Storage encryption mechanisms to render victim blobs inaccessible and extort ransom without any CVE or malware payload. Datadog Security Labs documents four methods: client-side encryption (used in the wild by BlackCat/ALPHV in 2023), customer-provided encryption keys (CPK), attacker-controlled encryption scopes (used in the wild by STORM-0501), and storage-service encryption with customer-managed keys (CMK), including cross-tenant CMK variants that place the unwrap key in an attacker-controlled Entra tenant.

- **Published:** 2026-06-15T00:00:00Z
- **Last reviewed:** 2026-06-15T00:00:00Z
- **Canonical:** https://intel.threadlinqs.com/threat/TL-2026-0810
- **ID:** TL-2026-0810
- **Severity:** HIGH
- **Category:** RANSOMWARE
- **Status:** ACTIVE
- **Actor:** STORM-0501
- **Detections:** 9 · **IOCs:** 16 (full data via the Threadlinqs MCP server — Purple tier)

## Description

This threat covers a class of cloud-native ransomware that weaponizes Azure Storage's own encryption features rather than deploying a traditional binary encryptor. Because the abuse relies on legitimate Azure REST API operations and headers, there is no CVE to patch; defense is a matter of configuration hardening, least privilege, and log-driven detection.

Method 1 — Client-side encryption: With only storage data-plane permissions (e.g. a compromised storage account access key or SAS token), an actor downloads blobs in bulk (GetBlob), encrypts them locally, and overwrites the originals (PutBlob). No Azure-native encryption feature is required. BlackCat/ALPHV used this approach in 2023 via its Sphynx encryptor against compromised Azure Storage accounts (reported by Sophos X-Ops).

Method 2 — Customer-provided encryption keys (CPK): The actor reuploads blobs supplying their own AES-256 key in HTTP request headers (x-ms-encryption-key, x-ms-encryption-key-sha256, x-ms-encryption-algorithm: AES256). The key never enters the victim tenant, so the data cannot be decrypted without the attacker. No public in-the-wild Azure reporting exists, but it is directly analogous to the AWS SSE-C abuse by the 'Codefinger' actor (Halcyon, January 2025). Critically, Azure resource logs do not record the x-ms-encryption-key-sha256 header, making CPK abuse nearly indistinguishable from normal writes.

Method 3 — Encryption scopes (most prevalent / observed): The actor creates a new Azure Key Vault and key in the victim tenant, creates an encryption scope bound to that key, reuploads blobs specifying x-ms-encryption-scope (or seeds a new container/account with the scope as default and uses CopyBlob), then deletes the key/vault to deny access. STORM-0501 used this technique (Microsoft, August 27 2025) — described as the most widely reported Azure Storage ransomware tactic. Encryption-scope usage on individual blob operations is not logged in storage resource logs, creating a detection gap; control-plane and Key Vault logs are the primary signal.

Method 4 — Storage Service Encryption with Customer-Managed Keys (CMK): A single control-plane PATCH points the storage account's encryption keySource to an attacker-controlled Key Vault key (Microsoft.Keyvault), requiring a SystemAssigned managed identity; deleting that key then makes Azure unable to unwrap its own storage key. This needs no data-plane operations and is the most efficient method. No public in-the-wild reporting yet.

Cross-tenant variants of Methods 3 and 4 host the encryption key in a separate attacker-controlled Entra tenant, linked via a multi-tenant application registration and federated identity credentials (FederatedIdentityCredentials) trusting the victim storage account's managed identity. This defeats Key Vault soft-delete/purge-protection recovery because the key lives outside the victim's control entirely. Soft-delete (90-day default, purge protection auto-enabled for storage-linked vaults) can also be circumvented by setting a 7-day minimum retention before linking and waiting for natural purge.

STORM-0501 more broadly pivots from on-prem Active Directory to Entra ID, abusing Directory Synchronization (Entra Connect) and registering malicious federated domains for persistent backdoor impersonation, using AzureHound/AzureHound-style discovery and AzCopy for mass exfiltration before destruction.

## MITRE ATT&CK

- T1078 Valid Accounts
- T1098 Account Manipulation
- T1136 Create Account
- T1484 Domain or Tenant Policy Modification
- T1578 Modify Cloud Compute Infrastructure
- T1685 Disable or Modify Tools
- T1552 Unsecured Credentials
- T1580 Cloud Infrastructure Discovery
- T1526 Cloud Service Discovery
- T1530 Data from Cloud Storage
- T1537 Transfer Data to Cloud Account
- T1486 Data Encrypted for Impact
- T1485 Data Destruction
- T1490 Inhibit System Recovery
- T1657 Financial Theft

## Sources

- [Holding blobs for ransom: Four methods for Azure Storage ransomware](https://securitylabs.datadoghq.com/articles/azure-blob-storage-ransomware-four-methods/)
- [Storm-0501's evolving techniques lead to cloud-based ransomware](https://www.microsoft.com/en-us/security/blog/2025/08/27/storm-0501s-evolving-techniques-lead-to-cloud-based-ransomware/)
- [Storm-0501 hackers shift to ransomware attacks in the cloud](https://www.bleepingcomputer.com/news/security/storm-0501-hackers-shift-to-ransomware-attacks-in-the-cloud/)
- [Microsoft details Storm-0501's focus on ransomware in the cloud](https://cyberscoop.com/storm-0501-ransomware-microsoft-threat-intelligence/)
- [Codefinger: Abusing AWS native services SSE-C for ransomware](https://www.halcyon.ai/blog/abusing-aws-native-services-ransomware-encrypting-s3-buckets-with-sse-c)
- [Stratus Red Team — cloud attack emulation (Azure ransomware techniques)](https://github.com/DataDog/stratus-red-team)
- [Azure Storage encryption for data at rest (CPK, encryption scopes, CMK)](https://learn.microsoft.com/en-us/azure/storage/common/storage-service-encryption)

## Full data

Detection queries (Splunk SPL / Microsoft KQL / Sigma) and IOC values require the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp

Canonical: https://intel.threadlinqs.com/threat/TL-2026-0810