Affected Systems
Cloudflare Workers running on AMD EPYC Zen 2 and Zen 3 processors (Linux). Attack targets V8 isolates within shared Worker processes. Affects multi-tenant serverless environments relying on language-level isolation. Mitigations deployed in production as of September 2025.
Exploitation Status
Proof-of-concept demonstrated by researchers in controlled production environment. No CVE assigned. Cloudflare reports no indicators of active exploitation over the past three years. Attack requires attacker-controlled Worker co-located with victim Worker in same process.
Business Impact
Researchers achieved 360x improvement over 2021 Spectre attack, leaking JWT at 12 bits/sec with 99.16% accuracy. Attack bypassed Dynamic Process Isolation (DyPrIs) by exploiting WebSocket timing channels and Durable Objects for long-lived sessions. Demonstrates cross-tenant data leakage risk in serverless platforms using shared processes. Cloudflare has deployed three-layer mitigation (improved DyPrIs, V8 Sandbox, MPK-based isolation). Organizations using Cloudflare Workers for sensitive workloads should verify current platform protections are active.
Urgency
🟡 Within a week
Recommended Actions
- Verify Cloudflare Workers deployments are running with September 2025 or later hardening measures (improved DyPrIs, V8 Sandbox, MPK-based isolation).
- Review Workers handling JWTs or other authentication tokens; consider rotating credentials as precautionary measure if Workers were active before September 2025.
- Audit use of Durable Objects and WebSocket-heavy Workers; these features enabled bypass of earlier DyPrIs protections.
- For high-sensitivity workloads, evaluate whether strict process isolation (e.g., separate containers or VMs) is required instead of language-level isolation.
- Monitor Cloudflare security advisories for additional guidance on Workers hardening and any follow-up patches.