Critical workerd Flaws Expose Cloudflare Workers Memory and Enable Code Mode Escape

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.