Greenshot Local Code-Execution Vulnerability (CVE-2025-59050) — CyberDudeBivash Alert By CyberDudeBivash (Bivash Kumar Nayak)

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Publish Date: 18-09-2025

Summary

Vulnerability ID: CVE-2025-59050
Affected Software: Greenshot ≤ version 1.3.300 (including GUI and any installed application using Greenshot.exe)
Vulnerability Type: Insecure deserialization via WM_COPYDATA IPC message handler
Impact: Local arbitrary code execution (RCE) at user level; attacker needs a local process, but exploit is relatively simple
Current Status: Proof-of-Concept (PoC) released; patched in version 1.3.301

What You Need to Know

The vulnerability allows a local process (which could be user-owned or via a compromised app) to send a crafted WM_COPYDATA message containing serialized .NET data, deserialized by Greenshot using BinaryFormatter.Deserialize without validation. This can be used to execute attacker-controlled code.
Many organizations use Greenshot (screenshot & annotation utility) as a lightweight tool. It’s often assumed non-threatening, which amplifies the risk.

Urgent Action Required

Patch now to Greenshot version 1.3.301 (or newer) — install across all managed endpoints.
Inventory where Greenshot is installed: find version numbers, locations, usage patterns.
Block or monitor IPC (WM_COPYDATA) from untrusted or unknown processes to Greenshot.exe.
Set up EDR / endpoint rules to detect unexpected child processes spawned by Greenshot, or unusual file writes after Greenshot activity.

Detection & Indicators

Unusual IPC (WM_COPYDATA) calls where the sender process is not trusted.
Greenshot.exe spawning child processes like cmd.exe, powershell.exe, or other execution binaries.
Creation of .exe / .dll / .ps1 files in user writable folders immediately following Greenshot.exe usage.
Event log entries or security logs showing SendMessage calls to Greenshot from other processes.
EDR alerts for deserialization behavior involving BinaryFormatter.

Recommended Mitigations

Upgrade to 1.3.301 immediately.
Restrict permissions: ensure Greenshot is not run elevated, remove unnecessary privileges.
Apply AppLocker / WDAC policies to control which applications can send messages via WM_COPYDATA.
Turn on enhanced logging for IPC and newly created child processes from Greenshot.
Educate users: don’t extract or execute files from untrusted sources or temp directories after screenshot/annotation workflows.

Incident Response Playbook (Quick Version)

Step	Action
Containment	Isolate affected host; disable Greenshot if unpatched.
Evidence Collection	Collect logs (IPC, process, file creation), any suspicious binaries or scripts, memory snapshot if possible.
Eradication	Remove malicious child processes, start-up entries; apply patch.
Recovery	Restore systems from clean backups, verify no persistence left.
Review & Prevention	Update detection rules, tighten policies, train users; consider banning or restricting Greenshot if risk judged too high.

Broader Insight from CyberDudeBivash

This is another example of how “trusted utility tools” are often overlooked in threat modeling. Attackers aren’t always going after big targets — they exploit weak links like screenshot tools, PDF viewers, annotation utilities, etc. Deserialization vulnerabilities in .NET have long been a pattern; responsible devs should avoid unsafe APIs where possible.

References & Further Reading

Github Advisory: GHSA-8f7f-x7ww-xx5w — Greenshot Security Advisory for CVE-2025-59050
NVD: CVE-2025-59050 record
Community write-ups / PoC analysis

#CyberDudeBivash #Greenshot #CVE2025 #WindowsSecurity #RCE #InsecureDeserialization #Alert #PatchNow

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