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Researchers disclosed a remote Spectre attack against Cloudflare Workers that extracted a JSON Web Token from a co-located Worker running in Cloudflare’s production environment at up to 12 bits per second. The attack targeted separate V8 isolates sharing the same process, using WebSocket communications as a remote timing source and long-lived Durable Objects to bypass assumptions in Cloudflare’s Dynamic Process Isolation (DyPrIs) design. Testing reportedly succeeded on Linux servers with AMD EPYC Zen 2 and Zen 3 processors, with lower system load improving leakage rates while slower exfiltration remained possible under heavier load.
Cloudflare said the research did not access customer data and that it found no signs of active exploitation during the past three years, but acknowledged limitations in its production isolation model and detailed hardening steps. The company said it mitigated the issue by improving DyPrIs, integrating the V8 Sandbox, and deploying MPK-based in-process isolation to better contain speculative-execution attacks in multi-tenant Worker environments. The disclosure highlights that speculative side-channel risks can persist even in sandboxed serverless platforms when attacker and victim workloads are co-located within the same process.
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Cloudflare said it mitigated the issue in production by improving Dynamic Process Isolation, integrating the V8 Sandbox, and deploying MPK-based in-process isolation. The company also said it found no indicators of active exploitation over the previous three years.
Researchers disclosed a remote Spectre attack that leaked a JSON Web Token from a co-located Cloudflare Worker in production at up to 12 bits per second with 99.16% accuracy. The demonstration used attacker- and victim-controlled Workers and did not access customer data.
Nearly five years before the 2026 disclosure, Cloudflare and TU Graz published research demonstrating a remote Spectre attack against Cloudflare Workers at 120 bits per hour and introduced Dynamic Process Isolation (DyPrIs) as a defense.
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Check Point Research disclosed five vulnerabilities in `workerd`, the open-source runtime behind Cloudflare Workers and Cloudflare Code Mode, describing two primary attack paths: cross-tenant memory exposure in the managed Workers environment and a sandbox escape in Code Mode that can lead to native code execution on the host in self-hosted deployments. The researchers said the issues stem from native C++ glue code and the `tcmalloc` heap operating outside core V8 isolation protections, creating exploitable conditions even where V8 sandboxing and memory protection keys are enabled. Cloudflare rated two of the flaws **Critical** and said fixes have already been deployed in the managed Workers production environment. Organizations running self-hosted deployments were advised to upgrade to `workerd v1.20260619.1`, while Check Point said it has released proof-of-concept code alongside its Black Hat USA 2026 presentation, increasing the urgency for defenders to validate patch status and review exposure in any self-managed `workerd` instances.
Aug 7, 2026
Researchers disclosed the **Meltdown** and **Spectre** hardware flaws, showing that speculative execution in modern processors could let attackers read sensitive data across security boundaries on affected devices. Reuters reported that **Meltdown** primarily affected Intel processors by breaking memory isolation, while **Spectre** impacted Intel, AMD, and ARM chips by tricking applications into leaking secrets such as passwords and other protected data. CERT/CC later summarized the broader issue as cache side-channel attacks against CPU hardware using speculative execution, underscoring that the weakness was architectural rather than limited to a single product line. Major vendors and cloud providers moved to contain the fallout with software, firmware, and microcode mitigations, including Microsoft Azure protections for hosted customers and public advisories from manufacturers such as Huawei. Subsequent research showed the problem persisted beyond the initial disclosures: the **ZombieLoad** attacks demonstrated additional Intel data-leakage paths tied to speculative execution, and a later **TSX Asynchronous Abort (TAA)** variant affected some processors previously thought to be resistant. Intel issued microcode updates, but researchers and vendors warned that mitigations reduced rather than eliminated risk, that exploitation generally required local code execution, and that fully disabling the underlying CPU behavior would carry significant performance costs.
Jun 29, 2026ETH Zurich has disclosed VMScape (CVE-2025-40300), a new Spectre-based attack that allows a malicious VM to leak secrets from the QEMU hypervisor on AMD Zen and Intel Coffee Lake CPUs. The attack exploits incomplete branch predictor isolation, bypassing existing mitigations and threatening multi-tenant cloud environments. Linux kernel patches have been released to mitigate the vulnerability with minimal performance impact.
Jun 29, 2026