An uncontrolled search path element vulnerability in GlavSoft TightVNC Server for Windows before 2.8.88 allows a local authenticated user to execute arbitrary code with SYSTEM privileges. DynamicLibrary::init() (and ThemeLib) load screenhooks32.dll / screenhooks64.dll with LoadLibrary() using a bare file name and no LOADLIBRARYSEARCH flags, so the TightVNC service follows the default DLL search order and loads an attacker-planted DLL from a writable directory earlier in that order (for example, an installation directory with permissive ACLs).

Incorrect permission assignment in GlavSoft TightVNC Server for Windows before 2.8.88 allows a local authenticated user to read or overwrite the inter-process communication handles used between the TightVNC service and its desktop server process. The named shared memory segment in the Global\ namespace that carries the pipe HANDLE values is created with a NULL DACL, and its name is derived from a time-seeded srand(time(0)) value that is predictable to one-second granularity. A low-privileged local process can open the mapping and tamper with the IPC channel of a service running as SYSTEM, potentially leading to disclosure of session data, privilege escalation, or denial of service.

An integer underflow in WinCursorShapeUtils::trimTransparent() in GlavSoft TightVNC Server for Windows before 2.8.88 allows a local authenticated user to crash the server, and potentially read out-of-bounds memory, by causing a cursor shape with a width or height of zero to be processed on the DXGI capture path. The loop bound width - 1 wraps to 0xFFFFFFFF, producing an access roughly 4 GB beyond the 64 KB cursor buffer; a monochrome cursor of height 1 also becomes 0 because getCursorHeight() halves the height in place.

A NULL pointer dereference vulnerability in the Win8ScreenDriver component of GlavSoft TightVNC Server for Windows before 2.8.88 allows an attacker to crash the server, causing a denial of service. When re-initialization of the DXGI Desktop Duplication driver fails in applyNewScreenProperties() (for example after a GPU reset, display hot-plug or session change), mdrvImpl is left NULL and is subsequently dereferenced without a check by executeDetection(), getScreenBuffer(), grabFb(), getScreenPropertiesChanged() and getCursorPosition().