Cloudflare fixes cross-tenant residual-data exposure in Containers

Cloudflare disclosed a Containers and Sandboxes vulnerability on 24 September after a researcher reported it on 4 September. Storage-block reuse could expose residual material from earlier containers on the same underlying host. A customer could not choose a specific victim or read another customer’s actively attached disk.

Cloudflare restored zeroing of newly allocated blocks, then retired affected running disks and cleared cached image snapshots so older mappings were recreated. The company said the fix was complete without customer configuration changes. Its investigation found activity attributable to authorised research and internal validation, with no other exploitation identified in retained telemetry. That is the company’s visibility-based finding, distinct from saying the original isolation flaw carried no potential exposure.