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ambar-src is a malicious npm package (software supply-chain malware) disclosed by Tenable. It was uploaded to npm on 2026-02-13 and reportedly reached >50,000 downloads before removal. The package abuses npm’s preinstall script hook to execute malicious code (index.js) during installation and then retrieves OS-specific payloads from x-ya[.]ru.
Behavior/capabilities by platform (as described):
Exfiltration/infrastructure: Tenable stated collected data is exfiltrated to a Yandex Cloud domain to blend with legitimate traffic.
Relationships/notes: Tenable assessed ambar-src is a more mature variant of the rogue npm package eslint-verify-plugin (previously flagged by JFrog), which was reported to drop Mythic agents Poseidon and Apfell on Linux and macOS.
Impact assessment: Tenable advised that systems where ambar-src is installed or running should be considered fully compromised, and that removing the npm package may not remove all resulting malware.
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3 distinct techniques documented for this family, organized by ATT&CK tactic.
Researchers at Tenable discovered the new technique, which they’re calling “download pumping,” while analyzing npm packages uploaded to the public registry... We observed this technique being used deliberately in the wild for the first time in our analysis of the malicious ‘ambar-src’ package, which reached more than 50,000 downloads in three days after attackers uploaded more than 700 versions.
When appraising the legitimacy of packages in software repositories, developers and even security tools often rely on download counts. Nonetheless, the metric can be weaponized by threat actors who use automated systems such as repository mirrors and analysis bots to poison software packages and infect supply chains.
3 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Malicious npm package used in a developer-targeting open-source/supply-chain compromise context.
Malicious npm package used as an open-source/supply-chain vector targeting developers.
Malicious npm package that executes during installation via a preinstall hook and pulls OS-specific payloads from attacker infrastructure: Windows downloads/executes msinit.exe containing encrypted shellcode loaded in-memory; Linux downloads a bash script that retrieves an ELF SSH-based reverse shell client; macOS drops the Mythic agent Apfell (JXA) for recon, screenshots, Chrome data theft, and password capture via fake prompt. Exfiltrates collected data to a Yandex Cloud domain to blend with legitimate traffic.
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Named campaigns wielding this family, with evidence pinned to each claim.
CVEs this family uses for access and lateral movement.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Every documented technique, ranked by evidence weight.
Reddit, Mastodon, and CTI community discussion around this family.