Executive Summary
In September 2026, security researcher Oren Yomtov discovered a critical vulnerability in Cloudflare Containers that allowed one customer's container to access leftover disk data from other customers' previously deleted containers. The flaw stemmed from improper disk provisioning configuration where deleted container blocks were returned to a shared pool without proper wiping, enabling cross-tenant data exposure. Researchers successfully recovered directory structures, SQLite databases, browser profiles, and credential files across 18 of 24 test attempts on production servers spanning four continents. Cloudflare fixed the issue by enabling proper block wiping and retiring all running containers, completing remediation on September 19, 2026.
This incident highlights the growing risks in multi-tenant cloud infrastructure as organizations increasingly adopt containerized workloads and AI-driven development environments, making proper data isolation and secure deprovisioning critical for preventing cross-customer data breaches.
Why This Matters Now
Multi-tenant cloud vulnerabilities are increasingly critical as organizations migrate sensitive workloads to shared infrastructure and adopt AI-powered development platforms, making cross-tenant data isolation failures a significant compliance and security risk.
Attack Path Analysis
Attacker exploited Cloudflare's container thin provisioning vulnerability to access leftover disk blocks from other customers' deleted containers. The attacker gained initial access by deploying containers on shared infrastructure, then leveraged the improper disk block wiping to read sensitive data including SQLite databases, credentials, and configuration files from previous tenants. This cross-tenant data exposure allowed potential privilege escalation through discovered credentials, lateral movement across customer environments, and exfiltration of sensitive information without detection.
Kill Chain Progression
This analysis maps confirmed threat intelligence to the full cloud kill chain to show where defensive gaps would emerge as an attack progresses.
Initial Compromise
Description
Attacker deployed containers on Cloudflare's shared infrastructure, exploiting the thin provisioning vulnerability where disk blocks were not properly wiped when reassigned between customers
MITRE ATT&CK® Techniques
Credentials In Files
Escape to Host
Data from Local System
Stored Data Manipulation
Data from Cloud Storage Object
Cloud Accounts
Disable or Modify Tools
Potential Compliance Exposure
Mapping incident impact across multiple compliance frameworks.
PCI DSS 4.0 – Cardholder Data Storage Protection
Control ID: 3.4.1
NYDFS 23 NYCRR 500 – Multi-Factor Authentication
Control ID: 500.15
DORA – ICT Third-Party Risk Management
Control ID: Article 8
CISA ZTMM 2.0 – Data Categorization and Protection
Control ID: Data Pillar
NIS2 Directive – Cybersecurity Risk Management Measures
Control ID: Article 21
ISO 27001 – Separation of Networks
Control ID: A.13.1.3
Sector Implications
Industry-specific impact of the vulnerabilities, including operational, regulatory, and cloud security risks.
Computer Software/Engineering
Container cross-tenant vulnerability exposes leftover disk data including databases, credentials, and .env files, compromising zero trust segmentation and multicloud visibility controls.
Information Technology/IT
Cloud infrastructure vulnerability enables data exfiltration from shared containers, violating east-west traffic security and egress policy enforcement across hybrid connectivity environments.
Financial Services
Cloudflare container flaw exposes sensitive customer data including SQLite databases and credential files, threatening PCI compliance and encrypted traffic requirements.
Health Care / Life Sciences
Cross-tenant data leakage violates HIPAA requirements for data protection, particularly affecting threat detection capabilities and secure hybrid connectivity for patient information.
Sources
- Cloudflare Fixes Flaw That Let One Container Read Another Customer's Leftover Disk Datahttps://thehackernews.com/2026/09/cloudflare-fixes-flaw-that-let-one.htmlVerified
- Cloudflare Containers Cross-Tenant Vulnerabilityhttps://blog.cloudflare.com/containers-cross-tenant-vulnerability/Verified
- Escaping the Cloudflare Sandboxhttps://accomplish.ai/blog/escaping-the-cloudflare-sandbox/Verified
Frequently Asked Questions
Cloud Native Security Fabric Mitigations and ControlsCNSF
Based on the attack progression modeled above, these are the defensive controls that would constrain each stage.
Aviatrix Zero Trust CNSF would have reduced the blast radius of this cross-tenant data exposure by constraining lateral movement paths and limiting the scope of credential-based pivoting across customer environments.
Control: Cloud Native Security Fabric (CNSF)
Mitigation: Workload isolation policies would likely have constrained the attacker's ability to access cross-tenant disk blocks by implementing stricter container boundary controls and resource allocation segmentation
Control: Zero Trust Segmentation
Mitigation: Microsegmentation policies would likely have limited the attacker's ability to access raw disk operations and cross-tenant credential files by restricting process-level access to sensitive system resources
Control: East-West Traffic Security
Mitigation: Traffic inspection and segmentation controls would likely have constrained credential-based lateral movement by blocking unauthorized inter-tenant communication paths and validating identity context for cross-environment access
Control: Multicloud Visibility & Control
Mitigation: Centralized visibility and policy enforcement would likely have detected and constrained persistent access patterns across geographic regions by monitoring anomalous cross-tenant activity and container behavior
Control: Egress Security & Policy Enforcement
Mitigation: Controlled egress policies would likely have constrained large-scale data extraction by monitoring and restricting outbound data flows containing sensitive cross-tenant information like databases and credential files
The residual impact would likely have been constrained to fewer affected customers and reduced data exposure scope, limiting the overall blast radius of cross-tenant credential compromise
Impact at a Glance
Affected Business Functions
- Cloud Computing Services
- Container Hosting
- Serverless Computing
- Multi-tenant Infrastructure
Estimated downtime: N/A
Estimated loss: N/A
Cross-tenant data leakage affecting Cloudflare Containers and Sandboxes customers. Exposed data included directory structures, SQLite databases, Chromium browser profiles, environment files, and credential files from other customers' containers. The vulnerability allowed reading up to 60KB of leftover data from previously allocated disk blocks across shared infrastructure.
Recommended Actions
Key Takeaways & Next Steps
- • Implement Zero Trust Segmentation with identity-based policies to prevent cross-tenant data access even in shared infrastructure scenarios
- • Deploy Multicloud Visibility & Control to detect anomalous disk access patterns and unauthorized data reads across container environments
- • Establish Egress Security & Policy Enforcement to monitor and control data exfiltration attempts from container workloads
- • Enable Threat Detection & Anomaly Response capabilities to baseline normal container behavior and alert on suspicious disk-level operations
- • Enforce Cloud Native Security Fabric controls with real-time inspection and distributed policy enforcement for container isolation and data protection
