Detect Notepad++ Download of Code Without Integrity Check (CVE-2025-15556) in Elastic Security
CVE-2025-15556 is a CWE-494 (Download of Code Without Integrity Check) vulnerability in Notepad++ that has been added to CISA's Known Exploited Vulnerabilities catalog. The vulnerability allows an attacker to deliver malicious code through Notepad++'s update or plugin mechanism without cryptographic integrity verification, enabling arbitrary code execution in the context of the user running Notepad++. This is actively exploited in the wild and should be treated as high-priority for endpoint detection and response.
MITRE ATT&CK
- Tactic
- Initial Access Execution Persistence
Elastic Detection Query
sequence by host.name with maxspan=5m
[process where process.name : "notepad++.exe" and event.type == "start"]
[any where
(
/* Suspicious network connection from notepad++ */
(event.category == "network" and process.name : "notepad++.exe" and
not destination.domain : ("*.notepad-plus-plus.org", "notepad-plus-plus.org"))
or
/* Child process spawned by notepad++ */
(event.category == "process" and process.parent.name : "notepad++.exe" and
not process.name : ("notepad++.exe", "GUP.exe", "conhost.exe"))
or
/* File write to plugin or updater directory */
(event.category == "file" and process.name : "notepad++.exe" and
file.path : ("*\\plugins\\*", "*\\updater\\*") and
file.extension : ("dll", "exe"))
)
]EQL sequence detection correlating Notepad++ process start with subsequent suspicious network connections, child process spawning, or plugin/updater directory file writes indicative of CVE-2025-15556 exploitation.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate plugin manager operations downloading plugins from official sources
- Auto-update mechanism (GUP.exe) performing standard version updates
- Administrative scripting that invokes Notepad++ as a component
- AV/EDR software intercepting Notepad++ file operations
Other platforms for CVE-2025-15556
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Simulate Notepad++ Downloading Unsigned DLL via HTTP
Expected signal: Sysmon Event ID 3 (network connection from notepad++.exe to non-official IP), Sysmon Event ID 11 (file creation in plugins directory with .dll extension), EDR network connection alert
- Test 2Notepad++ Plugin Directory DLL Drop
Expected signal: Sysmon Event ID 11 for file creation in Notepad++ plugins directory with .dll extension; EDR file creation alert
- Test 3Notepad++ Spawning Unexpected Child Process
Expected signal: Sysmon Event ID 1 showing cmd.exe with Notepad++ as parent process; EDR process lineage alert; command line captured in telemetry
Unlock Pro Content
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