Cloudflare Containers (Product): news timeline & CVEs

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.

GBHackersSep 25, 05:52 UTC · 2d agoVulnerability 4 sources

Cloudflare Fixes Flaw That Let One Container Read Another Customer's Leftover Disk Data

Cloudflare fixed a Containers flaw that exposed other customers' leftover disk data.

Cloudflare and researchers said a flaw in Cloudflare Containers, which also underlies Cloudflare Sandboxes, let a customer read data previous containers left on shared disks. Thin-provisioned 64 KB blocks were returned to a cross-account pool without wiping, so a 4 KB write still exposed the rest of a prior tenant's block. Production tests recovered leftovers on 18 of 24 attempts, including directory listings, SQLite databases, Chromium profiles, .env files, and credential files. Oren Yomtov of Accomplish reported it on September 4; Cloudflare restored wiping, cleared existing disks by September 19, and said retained logs showed only authorized testing.

The Hacker Newsupdated Sep 25, 05:52 UTC · 2d agofirst Sep 25, 04:49 UTC · 2d agoVulnerability 4 sources

Cloudflare Containers Vulnerability Could Leak Data Between Customer Workloads

Cloudflare patched a Containers flaw that could let one tenant read residual disk data from another.

Cloudflare patched a cross-tenant data exposure flaw in Containers, which also underlies Cloudflare Sandboxes. Device-mapper thin provisioning with skip_block_zeroing recycled uncleared 64 KiB blocks, so a new container could read leftover bytes after writing only 4 KiB. Oren Yomtov of Accomplish disclosed it on September 4, 2026 via HackerOne. Residual foreign data, including SQLite pages, appeared on many production placements, but Cloudflare found no malicious exploitation and retired existing disks.

Cyber Security Newsupdated Sep 25, 05:52 UTC · 2d agofirst Sep 25, 03:13 UTC · 2d agoVulnerability 4 sources

How Cloudflare addressed a cross-tenant data exposure vulnerability in Containers

Cloudflare fixed a Containers flaw that could expose residual cross-tenant disk data; no malicious exploitation was found.

On September 4, 2026, Accomplish researcher Oren Yomtov responsibly reported a cross-tenant data exposure in Cloudflare Containers and Sandboxes. Containers run in Firecracker VMs with Linux dm-thin provisioning and skip_block_zeroing, so a 4 KiB write into a reallocated 64 KiB block could leave up to 60 KiB of a previous customer's data readable. A Workers Paid customer could not choose the host or target a specific tenant, but researchers found residual directory, database, and SQLite data on 18 of 24 placements. Cloudflare says the fleet is fixed, no customer changes are required, and telemetry showed no malicious exploitation.

Cloudflare Blogupdated Sep 25, 05:52 UTC · 2d agofirst Sep 24, 15:00 UTC · 2d agoVulnerability 4 sources1

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Cloudflare Containers Flaw Could Expose Data From Other Customers’ Workloads

Cloudflare Fixes Flaw That Let One Container Read Another Customer's Leftover Disk Data

Cloudflare Containers Vulnerability Could Leak Data Between Customer Workloads

How Cloudflare addressed a cross-tenant data exposure vulnerability in Containers