guest-app-uinpm
Advisory published Updated
guest-app-ui is a confirmed malicious npm package (MAL-2026-10096) that opens a backdoor for remote access (malicious version 99.0.0). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in guest-app-ui (npm)
What this malware does
Package publishes as version 99.0.0 under a name presented in its README as an unclaimed internal name, positioning it to win dependency-confusion resolution against private registries. Both preinstall and postinstall lifecycle hooks in package.json execute callback.js, which collects installer host identifiers (os.hostname(), process.env.USER, process.cwd(), __dirname, platform/release, internal IPv4 addresses, and process.env.npm_config_registry), base64url-encodes the payload, and transmits it over three redundant channels to the hardcoded host 4li9yfz7.instances.httpworkbench.com: a DNS lookup/resolve4 with the payload as a subdomain label, an HTTP POST, and an HTTPS POST with TLS verification disabled (rejectUnauthorized: false). Any organization that has a private package by this name and lacks a scope/registry pin will pull this public artifact on npm install and beacon host fingerprint data to the external interaction host. The self-labeling as an authorized research PoC does not gate the behavior — every installer of this name is fingerprinted unconditionally.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Backdoor / remote accessFind it
Search your lockfiles and build artifacts for guest-app-ui (version 99.0.0).
If you installed it — respond
guest-app-ui establishes remote access, so treat any host that installed it as fully compromised. Isolate the machine, remove the package, rotate all credentials it could reach, and rebuild from a trusted image rather than cleaning in place — a backdoor may have planted additional persistence.
Did it already run?
If guest-app-ui was installed, its post-install payload may already have run. Removing the package does not undo that — check outbound connections and credential use from the install window onward.
Frequently asked questions
Campaign
References
Credits
- Amazon Inspector · finder
Detect & block this
O3 blocks guest-app-ui-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the C2 callback and severs the channel.