Check Point Research discovered five memory-corruption vulnerabilities in workerd, the open-source runtime underlying both Cloudflare Code Mode and Cloudflare Workers. Two were rated Critical by Cloudflare: a use-after-free in node:zlib's deflateParams() and a use-after-free in HTMLRewriter's AttributesIterator. The researchers demonstrated two end-to-end exploits: a cross-tenant secret theft via a URLPattern out-of-bounds read on the shared tcmalloc heap (bypassing V8 sandbox and MPK), and a Code Mode sandbox escape from prompt injection to native host RCE via the zlib UAF. All bugs operate on the tcmalloc native heap, which is explicitly outside the V8 sandbox cage and memory protection keys. Cloudflare's managed environment is patched; self-hosted deployments must update to workerd v1.20260619.1. No CVEs have been assigned.
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When Agentic Glue Melts: Exploiting Cloudflare Code Mode and Workers