Executive brief
Sandboxie-Plus is an isolation tool used to run applications in a secure 'sandbox' to prevent them from making permanent changes to the host computer. A security flaw in the software's GUI service allows malicious programs running inside the sandbox to break out and execute code on the main system. This bypasses the primary security purpose of the software, potentially allowing malware to infect the host computer or access sensitive user data.
Technical details
An unrestricted APC injection vulnerability exists in the GuiServer service (GuiServer.cpp) due to improper validation in the GuiServer::WndHookRegisterSlave and GuiServer::WndHookNotifySlave functions. A sandboxed process can send a GUI_WND_HOOK_REGISTER request with an arbitrary thread ID and function pointer. Because the service runs with SYSTEM privileges, it successfully opens the target thread with THREAD_SET_CONTEXT and executes QueueUserAPC using the attacker-supplied parameters. This allows a sandboxed process to escape its isolation and execute arbitrary code in any unsandboxed process on the host. The issue is fixed in version 1.17.6 (Plus) and 5.72.6 (Classic) by verifying that the target thread belongs to the calling sandboxed process.
Affected products
- sandboxie-plus Sandboxie-Plus < 1.17.6
- sandboxie-plus Sandboxie < 5.72.6
Timeline
- 2026-05-17: patched: Version 1.17.6 released
- 2026-05-22: advisory: GitHub Security Advisory published
- 2026-07-15: disclosed: CVE published to NVD