Topic
A security principle for shared systems requiring that one customer's data, compute, or resources stay inaccessible to other tenants.
Cloudflare has fixed a flaw in Containers that let a Workers Paid account read the 60 KiB it had not written inside each 64 KiB disk block it touched. The fleet-wide fix needed no customer configuration changes.
Reality
Cloudflare Containers let a paying tenant read up to 60KiB of another customer's leftover data from each reused 64KiB disk block. Cloudflare has zeroed new blocks and rebuilt pre-fix disks, so the risk still open is plaintext credentials stored there earlier.
Reality
Cloudflare fixed a Containers flaw that let paying customers read other tenants' leftover disk data, found on 18 of 24 production tries. Sandboxes, the product it sells for running untrusted and AI-written code, was affected too.
Perspective Coverage
3 publishersReality
Researchers read a token out of a co-located Worker in Cloudflare's production fleet, 360 times faster than the 2021 demo that justified language-level isolation.
Reality
The code containers could not reach the internet or each other, but every one of them reached the same package service, and its metadata was not scoped by account, so a planted prompt turned one user's assistant into a stranger's Gmail reader.
Perspective Coverage
3 publishersReality
Password-reset queries made up 38% of one support RAG bot's vector lookups, says a dev.to write-up that moves retrieval behind an HTTP cache. Any saving depends on identical queries repeating within one tenant inside five minutes.
Reality
Salesforce's Cloud Atlas team rebuilt rate limiting for its identity store around coordinator-free global quotas and load shedding to protect five nines. The diagnosis fits any shared tier-0 service, though the published account stops before showing how the quotas stay in sync.
Reality
Benchling runs agent-written scientific code in a separate AWS account with no internet gateway and no NAT gateway, so the remaining way out of the VPC was a name lookup. The resolver policy answers the endpoints Benchling listed and blocks everything else.
Reality
Check Point's Alexey Bukhteyev told Lets Data Science that the test containers could not reach each other directly while both could still write metadata to the same package service, using credentials already present inside them.
Reality
A daily email worker in a Next.js monorepo read a shared queue with no tenant scope, and the obvious one-line filter passed a Jest suite that had only ever seeded one organization. The rewrite discovers tenants first.
Reality
A developer who builds one of the six persistent memory systems he checked walks through how each can stop sharing while Cursor and Claude Code both report a healthy connection. The split happens at the account, and nothing logs it.
Reality
OpenAI isolated code-interpreter containers per user account, then let all of them read and write the same Artifactory-backed package metadata so they could install software. The metadata carried an instruction into someone else's session.
Reality
A dev.to walkthrough CNAMEs a customer subdomain to platform storage and keeps every permission in the signature. Its sample onboarding code puts the tenant check before the presign call, where it belongs.
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Strong read-after-write consistency and conditional writes are real guarantees, but only two of the four database behaviours they stand in for have an enforcement point in the service, and the other two are convention.
Reality
cPanel says every supported build of cPanel and WHM is affected by CVE-2026-67401, and its September 8 advisory arrived without a severity score or any interim step for hosts that cannot take the upgrade yet.
Reality
API Platform checks authorization per operation, so the guard on the POST told a reviewer nothing about the GET declared on a different entity, and the provider behind that GET trusted the store id in the path.
Reality
Databricks says an ordinary customer role could reach the unchecked array index. The repair went upstream into the open-source extension rather than into either fleet. That is the only version that helps anyone else.
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ENABLE ROW LEVEL SECURITY leaves the table owner exempt, so an app account that owns its tables still reads every tenant. One developer built the same table five ways and found only one of the five sound.
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The leak ran at 99% accuracy and traced to a limitation in Dynamic Process Isolation, the heuristic that quarantines suspicious Workers. Detection was never the durable layer.
Reality
A read-only sensor for cross-tenant memory leaks ships with no tagged release, because its own backend cannot enumerate what the retriever exposed. That limitation is the story.
Reality
Build · August 17, 2026 · 1 publisher