The North Korean state-sponsored threat actor Sapphire Sleet is behind the Mastra supply chain attack that hit over 140 NPM packages last week, Microsoft reports.
Mastra is an open source TypeScript framework for building AI agents, workflows, and RAG pipelines. It offers integrations for major LLM providers, MCP servers, and cloud deployments.
The supply chain attack occurred on June 17. During a 45-minute window, the hackers published 141 packages that contained the malicious dependency easy-day-js, a typosquat of the legitimate dayjs date library.
The affected Mastra packages have approximately 8 million weekly downloads. All users who installed a @mastra package during the attack window on June 17 should consider their systems affected.
As part of the attack, the hackers compromised the ‘ehindero’ NPM maintainer account, which has publishing rights across the Mastra ecosystem. One day before the account takeover, the attackers published a clean version of easy-day-js to a separate account, ‘sergey2016’.
The threat actor used the compromised maintainer account to add easy-day-js as a dependency to 141 NPM packages across the Mastra ecosystem, in such a manner that the latest version of the library would always be installed, and then published the modified packages to NPM.
Simultaneously, they published a new, malicious version of the easy-day-js library to their account.
An obfuscated postinstall dropper in the dependency would fetch a second-stage payload from the attackers’ servers, write it to the temp directory, execute it as a detached, hidden background process, and then delete itself to hide its tracks.
“Because the payload executes during installation, any developer workstation or continuous integration and continuous delivery (CI/CD) pipeline that ran npm install or npm update after the compromised versions were published was potentially exposed, regardless of whether the package was imported in application code,” Microsoft says.
Targeting Windows, macOS, and Linux, the malware was designed to masquerade as node-related tools while collecting system information and targeting more than 160 cryptocurrency-related browser extensions.
Microsoft has attributed the attack to the financially motivated North Korean group Sapphire Sleet, also known as BlueNoroff, CageyChameleon, Copernicium, and Stardust Chollima, which was also blamed for the Axios supply chain attack.
In April, hackers published modified versions of the Axios NPM library that were pointing to a phantom dependency designed to download and execute a cross-platform RAT. Google’s Threat Intelligence Group attributed the attack to UNC1069.
Mastra users are advised to remove the affected package versions, check their systems for malware, rotate credentials, tokens, and other secrets, and harden access to their crypto-wallets.
Cybersecurity firms Aikido, Ox, Socket, Sonatype, and StepSecurity have published technical details and indicators of compromise (IoCs) associated with the Mastra supply chain attack.
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