Description

A serious vulnerability, CVE-2025-59050, has been found in the widely used Windows screenshot utility Greenshot, versions up to 1.3.300. The vulnerability enables local attackers to run arbitrary code inside the trusted `Greenshot.exe` process, without the need to elevate privileges. The vulnerability lies in unsafe processing of Windows WM\_COPYDATA messages. Greenshot unserialize-trusted input through the risky `.NET BinaryFormatter.Deserialize()` method, allowing execution of malicious code from any local process that sends a specially crafted message to the program. This in-process code execution method is most risky in corporate settings. Because the payload executes within Greenshot.exe, it escapes endpoint protection mechanisms such as AppLocker or Windows Defender Application Control (WDAC), which depend on observation of new or unknown process starting. A proof-of-concept showed successful spawning of `cmd.exe` with Greenshot as the parent process, proving the attack succeeds without writing to disk bypassing many conventional file-based security controls. The exploit can be caused by only local access and is triggered by `SendMessage` API calls. As a mitigation step, the users need to upgrade to Greenshot 1.3.301, dated September 16, 2025, which fixes the deserialization vulnerability by introducing input checks and hardening IPC handling. Organizations need to give this patching high priority, particularly in shared workstation or enterprise environments where local access is easier. Download only the patched version from the official Greenshot website at [getgreenshot[.]org](https://getgreenshot[.]org) to prevent tampered binaries. This bug highlights the risks of insecure deserialization in desktop applications and the need for secure inter-process communication practices.