Researchers have demonstrated a working Spectre attack against Cloudflare Workers — the serverless compute platform running at the edge of the internet — that successfully extracted a JSON Web Token from a co-located Worker in a live production environment. The kicker: it does so at up to 12 bits per second, which sounds glacial until you realise it's 360 times faster than the previous benchmark set in 2021.

Spectre, for the uninitiated, is a class of hardware vulnerability disclosed back in 2018 that exploits the way modern processors speculatively execute code. The short version: a malicious process can trick a CPU into briefly touching memory it shouldn't, then measure the timing of that access to infer what was there. Chip makers and cloud vendors spent years patching, mitigating, and generally hoping the problem would quietly go away. It hasn't.

What makes this finding significant is that it works against a hardened, real-world production environment — not a lab simulation. Cloudflare Workers isolates tenants using V8 isolates rather than traditional virtual machines, which is faster and cheaper but places more trust in software-level sandboxing. The researchers used an attacker-controlled Worker and a victim Worker side by side, the same way two unrelated customers might be co-located on Cloudflare's infrastructure, and leaked a JWT — a credential used to authenticate API calls — from the victim's memory.

JWTs are valuable targets. They're the keys that say "this request is authorised," and stealing one lets an attacker impersonate the legitimate service until the token expires or is revoked. In a real attack scenario, the leaked token could be used to make authenticated API calls, pivot deeper into a target's infrastructure, or access data the attacker was never meant to see.

Cloudflare has been notified and is working on mitigations. The company has long acknowledged that shared-hardware isolation is a hard problem, and has previously invested in techniques like timer resolution reduction and process isolation to blunt Spectre-style attacks. But the research suggests those defences haven't kept pace with attacker ingenuity.

The broader implication is uncomfortable for the entire serverless and edge-compute industry. The economics of shared infrastructure — many tenants, one machine — are fundamentally in tension with the assumption that tenant workloads are fully isolated. Every major cloud provider runs some variant of this model. AWS Lambda, Google Cloud Run, Azure Functions: all of them are betting that software isolation is good enough. This research is a data point suggesting it may not be.

For Australian organisations using Cloudflare Workers — and there are many, given Cloudflare's widespread deployment across Australian enterprise and government — the immediate action item is to rotate JWTs and other short-lived credentials regularly, treat edge compute as a partially-trusted environment, and avoid storing high-value secrets in Worker memory any longer than necessary.

The full research paper is expected to be published shortly. Watch for Cloudflare's formal response, which will likely include changes to timer resolution and potentially new guidance on sensitive workloads.