Cloudflare Containers Flaw Could Expose Data From Other Customers’ Workloads
Cloudflare patched a Containers disk-reuse flaw that could expose residual data from other customers' workloads.
Cloudflare remediated a cross-tenant data-exposure flaw in Cloudflare Containers, also affecting Sandboxes and Browser Rendering, reported on September 4, 2026, by Oren Yomtov of Accomplish. Writable disks used Linux dm-thin with skip_block_zeroing, so a newly assigned 64 KB block could retain up to 60 KB of a previous tenant's data, including filesystem metadata, SQLite pages, or .env contents. The proof of concept could not target a specific customer or live disk. Cloudflare removed the unsafe option, retired old disks, and said telemetry showed no malicious exploitation.
- Cloudflare fixed a cross-tenant residual-data flaw in Containers.
- dm-thin with skip_block_zeroing reused uncleared 64 KB disk blocks.
- Sandboxes and Browser Rendering used the same disk implementation.
- A Workers Paid customer could read leftover data but not target a victim.
- Cloudflare found no malicious exploitation and said customers need no action.
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From the original article
2 min read at gbhackers.com
Cloudflare has addressed a cross-tenant data exposure vulnerability in its Containers platform that could have allowed one customer’s workload to recover residual data belonging to other customers on the same infrastructure. This flaw also affected Cloudflare Sandboxes and the Browser Run service within Browser Rendering, both of which utilize the same underlying disk implementation. Cloudflare […]
By Divya · gbhackers.com
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