Overview
In this blog post, we will be delving into the details of a critical vulnerability that was discovered in Greenshot, a popular open-source screenshot utility for the Windows operating system. This vulnerability, identified as CVE-2025-59050, could allow an attacker to execute arbitrary code in the Greenshot process, potentially leading to a system compromise or data leakage. This vulnerability is of significant concern due to the high potential for harm and the wide user base of Greenshot.
Vulnerability Summary
CVE ID: CVE-2025-59050
Severity: High (8.4)
Attack Vector: Local
Privileges Required: Same integrity level as the Greenshot process
User Interaction: None
Impact: Potential system compromise or data leakage
Affected Products
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Product | Affected Versions
Greenshot | 1.3.300 and earlier
How the Exploit Works
The vulnerability resides in a WM_COPYDATA message handling logic within Greenshot. The vulnerable logic is found in a WinForms WndProc handler for WM_COPYDATA (message 74), which deserializes the data received without prior validation or authentication. This allows a local process running at the same integrity level as Greenshot to execute arbitrary code within the Greenshot process.
Moreover, the authorization check only occurs after deserialization, which means that any gadget chain embedded in the serialized payload executes regardless of channel membership. Therefore, a local attacker who can send WM_COPYDATA messages to the Greenshot main window can achieve in-process code execution.
Conceptual Example Code
While we do not want to provide a real exploit code for obvious reasons, a conceptual example would look something like this:
// Creating the WM_COPYDATA message
COPYDATASTRUCT cds;
cds.dwData = (IntPtr)1;
cds.cbData = size_of_payload;
cds.lpData = pointer_to_payload;
// Sending the message to the Greenshot main window
SendMessage(Greenshot_main_window_handle, WM_COPYDATA, IntPtr.Zero, ref cds);In this example, `size_of_payload` and `pointer_to_payload` would be replaced with the size and pointer to the malicious serialized payload. The payload would contain a gadget chain that, when deserialized, leads to execution of the attacker’s code.
Recommended Mitigation Guidance
The best way to mitigate the risk posed by this vulnerability is by applying the vendor’s patch. Greenshot has fixed this issue in version 1.3.301. As there are no known workarounds, it is strongly recommended to update to the latest version as soon as possible.
In addition, utilizing a Web Application Firewall (WAF) or Intrusion Detection System (IDS) could provide temporary mitigation by blocking or alerting on anomalous behavior associated with the exploit. However, this is not a permanent solution and should only be used as an interim measure until the patch can be applied.
