Cross‑Tenant Data Exposure Vulnerability in Cloudflare Containers Fixed After Responsible Disclosure
What Happened — Cloudflare identified a storage‑allocation misconfiguration in its multi‑tenant Containers and Sandboxes service that could let a tenant read residual disk blocks from a previous container on the same host. The flaw was responsibly disclosed by a researcher, patched fleet‑wide, and no customer data was found to be compromised.
Why It Matters for Trust & Control Assurance
- Demonstrates the need for continuous verification that storage‑provisioning controls enforce strict data segregation across tenants.
- Highlights the importance of real‑time configuration monitoring and auditable evidence that remediation actions have been applied.
- Aligns with the control objective of “segregated data handling and secure storage” that underpins many frameworks (e.g., NIST CSF 2.0, ISO 27001).
Who Is Affected – Cloud service providers offering shared‑infrastructure containers; SaaS platforms that run customer workloads on multi‑tenant hosts.
Recommended Actions – Review your container‑orchestration storage settings for block‑zeroing; enable continuous monitoring of storage‑layer configurations; capture remediation evidence for audit readiness. Source: https://blog.cloudflare.com/containers-cross-tenant-vulnerability/
Technical Notes – The issue stemmed from the skip_block_zeroing option in Linux dm‑thin thin provisioning, which left 64 KiB blocks partially un‑zeroed when reassigned. Exploitation required a tenant with a Workers Paid account to write small aligned blocks and read leftover data. No CVE was assigned; Cloudflare issued a vendor patch. Source: https://blog.cloudflare.com/containers-cross-tenant-vulnerability/