CVE-2026-12067: AvastSvc denial of service via unhandled JsonCpp exceptions in native message handlers

Missing exception handlers in AvastSvc native message dispatcher (ashServ.dll) on Windows allow a local, unprivileged attacker to crash the service by sending specially crafted JSON messages.

The vulnerability spans multiple handler pathways in the RPC-based native message protocol:

LogNmSvc.message handler: converts JSON fields to strings without type validation and without exception boundaries.  OpenInSzNmSvc handler: converts URL and origin fields to strings without type checking, exposing an exception. OpenInSzNmSvc.profile handler: converts the profile field to an integer without validation.

In all three cases, the exceptions are not caught by action-specific handlers and propagate up the dispatcher. The common root cause is the absence of try-catch blocks around JSON type conversions in the native message processing chain.