ChainDrop supply chain compromise: Anatomy of a self-propagating worm

Microsoft Threat Intelligence identified a large-scale npm supply chain attack affecting more than 400 packages across multiple unrelated publishers, including packages associated with major enterprise software ecosystems such as keyv, flat-cache, cache-manager, and others. The malicious releases contain a Mini Shai-Hulud variant, a self-propagating credential-stealing worm delivered through a large, heavily obfuscated Bun-based JavaScript payload. The malware typically executes automatically through an npm preinstall lifecycle hook before package installation completes.

Once executed, the malware searches developer workstations and continuous integration and continuous delivery (CI/CD) environments for npm, GitHub, cloud, and infrastructure credentials. It uses recovered identities to authenticate to npm, GitHub, Amazon Web Services (AWS), Kubernetes, and HashiCorp Vault, enabling it to enumerate packages, repositories, workflow secrets, cloud parameters, and secret-store values. Collected data is encrypted and transmitted through an attacker-controlled HTTPS endpoint, with GitHub repositories serving as a fallback exfiltration channel.

The payload’s most significant capability is automated propagation. After obtaining an npm publishing token, it enumerates packages available to the compromised identity, downloads their latest tarballs, inserts the malware and setup loader, adds a preinstall hook, increments the patch version, and republishes the modified packages. The malware can also use stolen GitHub credentials to inject Claude and Visual Studio Code configuration files into repositories, establishing persistence and creating an additional developer-to-developer infection path.

In this blog, we’re sharing our analysis of this supply chain attack, along with protection, detection, amd hunting guidance. Organizations that installed an affected package with lifecycle scripts enabled should treat the associated developer workstation or build runner as potentially compromised. Investigations should prioritize credentials accessible to the affected identity, unauthorized npm releases, unexpected repository or workflow modifications, suspicious cloud and secret-store access, and artifacts produced by affected build systems. Organizations should revoke and rotate exposed credentials from a known-clean environment and rebuild affected systems and downstream artifacts from trusted sources.

Attack chain overview

The campaign appeared as a rapid sequence of unauthorized patch releases across more than 400 npm packages maintained by otherwise unrelated publishers. Many malicious versions had no corresponding source-code commit, pull request, tag, or legitimate release, indicating that the attackers modified and published package tarballs directly rather than compromising each public source repository.

Affected releases typically added a preinstall lifecycle script that launched a malicious file, setup.mjs, contained within the package, which launched the large, obfuscated Bun JavaScript bundle included in the package. Because npm runs preinstall scripts before installation completes, the payload could execute on developer workstations and build runners before application tests or conventional security checks began.

After execution, the malware performs the following actions:

1. Determines whether it is running on a developer workstation or in a CI/CD environment. On workstations, it detaches itself to continue after installation; on CI/CD systems, it remains in the active job to access workflow secrets, runner credentials, and OpenID Connect (OIDC) publishing permissions. Both paths could support further package or repository propagation when suitable credentials are found.
2. Collects credentials from local files, environment variables, command-line tools, and GitHub Actions runner memory.
3. Authenticates to npm, GitHub, AWS, Kubernetes, and HashiCorp Vault to enumerate additional accessible resources and secrets.
4. Encrypts and exfiltrates collected data through an HTTPS channel, using GitHub repositories as a fallback.
5. Uses recovered npm publishing access to modify and republish additional packages.
6. Uses GitHub credentials to inject files into Claude and Visual Studio Code configurations across repository branches for persistence.

The payload’s  package-propagation routine downloads each publisher’s latest release, inserts itself, increments the patch version, and publishes the resulting archive. This mechanism can rapidly transform one compromised npm identity into many malicious package releases.

0. Initial publisher access

Evidence points towards stolen maintainer credentials as the attack vector for initial compromise. Later propagation used stolen npm publishing tokens and, in targeted workflows, GitHub Actions OIDC publishing access.

1. Payload startup and background execution

 The malicious npm package uses a lifecycle hook to launch its bundle.

During preflight, the payload checks the environment, exits on Russian-language systems, avoids duplicate instances, and starts a detached copy in the background on developer systems.

In CI environments, the payload remains attached so it can access credentials available to the active build job.

2. Initial credential discovery

The payload first collects information that is immediately available from the local system, shell, and GitHub Actions runner.

The shell collector attempts to obtain the GitHub CLI token and captures the values of all process environment variables. The filesystem collector searches credential files, shell histories, cloud configurati

Key Takeaways

• ChainDrop is a self-propagating worm targeting software supply chains.
• Microsoft Security details the attack chain and provides mitigation guidance.
• Organizations should review indicators of compromise and apply protections.