Greenshot up to 1.3.300 WinForms WndProc Greenshot.exe deserialization

Summaryinfo

A vulnerability was found in Greenshot up to 1.3.300. It has been rated as problematic. Affected by this vulnerability is an unknown functionality of the file Greenshot.exe of the component WinForms WndProc Handler. Performing a manipulation results in deserialization. This vulnerability is known as CVE-2025-59050. Attacking locally is a requirement. No exploit is available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Greenshot up to 1.3.300. It has been classified as problematic. This affects an unknown function of the file Greenshot.exe of the component WinForms WndProc Handler. The manipulation with an unknown input leads to a deserialization vulnerability. CWE is classifying the issue as CWE-502. The product deserializes untrusted data without sufficiently verifying that the resulting data will be valid. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

Greenshot is an open source Windows screenshot utility. Greenshot 1.3.300 and earlier deserializes attacker-controlled data received in a WM_COPYDATA message using BinaryFormatter.Deserialize without prior validation or authentication, allowing a local process at the same integrity level to trigger arbitrary code execution inside the Greenshot process. The vulnerable logic resides in a WinForms WndProc handler for WM_COPYDATA (message 74) that copies the supplied bytes into a MemoryStream and invokes BinaryFormatter.Deserialize, and only afterward checks whether the specified channel is authorized. Because the authorization check occurs after deserialization, any gadget chain embedded in the serialized payload executes regardless of channel membership. A local attacker who can send WM_COPYDATA to the Greenshot main window can achieve in-process code execution, which may aid evasion of application control policies by running payloads within the trusted, signed Greenshot.exe process. This issue is fixed in version 1.3.301. No known workarounds exist.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2025-59050 since 09/08/2025. The exploitability is told to be easy. Attacking locally is a requirement. Technical details of the vulnerability are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 265429 (Greenshot < 1.3.301 Deserialization of Untrusted Data (CVE-2025-59050)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 1.3.301 eliminates this vulnerability. Applying the patch f5a29a2ed3b0eb49231c0f4618300f488cf1b04d is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at Tenable (265429). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Name

• Greenshot

Version

• 1.0
• 1.1
• 1.2
• 1.3.300

License

• open-source

Website

• Product: https://github.com/greenshot/greenshot/

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