AIKIDO-2026-123108

TL;DR

Native jsg::Function objects in the workerd runtime can free themselves while they are still being invoked. jsg::Function::operator() called native functions through a bare reference into the owning Ref, so a native callback that runs JavaScript can drop that reference mid-call and leave a dangling pointer on the stack. The reachable case is TextEncoderStream, whose transform algorithm is a native lambda: a user-supplied toString() that cancels the readable side can clear the algorithms and free the function while it is still executing. Before the fix this use-after-free can crash the host process or corrupt runtime memory. The fix holds a reference for the duration of the call so the function is not accessed after it has been freed.