Sandboxie-Plus is an open‑source sandbox isolation software for Windows. Prior to version 1.17.6, the GuiServer::WndHookRegisterSlave function in sandboxie/core/svc/GuiServer.cpp stores attacker‑supplied hthread and hproc fields from a GUI_WND_HOOK_REGISTER request without validating that the thread belongs to the sandboxed process or that the function pointer is in the caller address space. GuiServer::WndHookNotifySlave later calls OpenThread(THREAD_SET_CONTEXT, FALSE, whk->hthread) and QueueUserAPC((PAPCFUNC)whk->hproc, hThread, (ULONG_PTR)req->threadid) with SYSTEM privileges, allowing a sandboxed process to execute arbitrary code in an unsandboxed host process. This issue is fixed in version 1.17.6.

Affected vendors include Sandboxie‑Plus; the product is called Sandboxie. All releases before version 1.17.6 are vulnerable. The issue was addressed in Sandboxie‑Plus 1.17.6 and later.

The CVSS base score of 7.7 indicates high severity, and the EPSS score of less than 1% suggests a low probability of exploitation at this time; the vulnerability is not listed in the CISA KEV catalog. Based on the description, the attack requires a sandboxed process to send a GUI_WND_HOOK_REGISTER request, after which the exploit can be triggered. The likely attack path involves opening a thread and queuing an APC to execute arbitrary code in the host process with SYSTEM privileges. These details about the attack vector and execution are inferred from the description and are not explicitly confirmed by the CVE data.