Notepad++ fell victim to a sophisticated supply chain attack orchestrated by state-sponsored threat actors who compromised its update infrastructure over a six-month campaign.
Security experts have attributed the attack to a Chinese state-backed group based on the highly selective targeting and technical sophistication demonstrated throughout the incident.
Attack Timeline and Scope
The compromise began in June 2025, when threat actors gained access to the shared hosting server that hosted Notepad++’s update management system.
According to the hosting provider’s investigation, attackers maintained persistent access until September 2, 2025, when a scheduled kernel and firmware update severed their direct connection.
However, the attackers retained access to internal services using stolen credentials, extending their ability to intercept and manipulate update traffic until December 2, 2025.
Rather than deploying malware indiscriminately, the attackers employed precision targeting, selectively redirecting update requests from specific users to attacker-controlled servers hosting malicious installer packages.
This refined approach demonstrates state-level capability and suggests knowledge of Notepad++’s update verification weaknesses in older versions.
The attack exploited insufficient cryptographic verification in Notepad++’s update mechanism.
The hosting provider’s logs reveal that attackers specifically searched for the Notepad++ domain, indicating prior reconnaissance of the application’s security posture.
They leveraged an infrastructure-level compromise rather than exploiting vulnerabilities in Notepad++’s code, enabling them to manipulate the getDownloadUrl.php endpoint and return malicious download URLs.
Notably, the provider found no evidence of secondary victims on the compromised server, confirming that Notepad++ was the sole target of this operation.
Notepad++ responded decisively by migrating to a new hosting provider with enhanced security architecture.
The WinGup updater was strengthened in v8.8.9 to verify both certificate and installer signatures.
Additionally, all XML responses from the update server are now digitally signed using XMLDSig standards, with mandatory verification enforcement launching in v8.9.2, expected within one month.
The hosting provider implemented comprehensive hardening measures, including credential rotation across all services and vulnerability patching, to prevent exploitation of known weaknesses.
This incident underscores the persistent threat supply chain attacks pose to software distribution ecosystems and highlights the critical importance of cryptographic verification in update mechanisms.
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