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.
- skip_block_zeroing left recycled 64 KiB dm-thin blocks uncleared across tenants.
- A 4 KiB write plus raw read exposed up to 60 KiB of prior data.
- Residual foreign data appeared on 18 of 24 placements, including SQLite databases.
- Attackers could not target a chosen victim, host, or specific data.
- Cloudflare zeroed new blocks, retired disks, and found no malicious exploitation.
- Vendors
- Cloudflare
- Organizations
- CloudflareAccomplishHackerOne
From the original article
3 min read at cybersecuritynews.com
Cloudflare has patched a cross-tenant data exposure vulnerability in its Containers platform across its global, multi-tenant cloud computing infrastructure that could allow one customer’s workload to recover residual disk data left by another tenant on the same physical host. The issue also affected Cloudflare Sandboxes, which is built on Containers, but Cloudflare says it found […]
By Guru Baran · cybersecuritynews.com
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