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

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 cyberdudebivash.com | cyberbivash.blogspot.com | cryptobivash.code.blog

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

  1. Patch now to Greenshot version 1.3.301 (or newer) — install across all managed endpoints.

  2. Inventory where Greenshot is installed: find version numbers, locations, usage patterns.

  3. Block or monitor IPC (WM_COPYDATA) from untrusted or unknown processes to Greenshot.exe.

  4. 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)

StepAction
ContainmentIsolate affected host; disable Greenshot if unpatched.
Evidence CollectionCollect logs (IPC, process, file creation), any suspicious binaries or scripts, memory snapshot if possible.
EradicationRemove malicious child processes, start-up entries; apply patch.
RecoveryRestore systems from clean backups, verify no persistence left.
Review & PreventionUpdate 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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