postcss-semantic-themes@1.0.0
This package appears in our research on the fake Tailwind CSS plugins, with how it works, the full package list and what to do if you installed it.
OpenSSF/OSV Malicious Advisory
imported 7h ago · by OpenSSF/OSVOpenSSF/OSV advisory MAL-2026-18334 confirms this npm version as malicious.
Advisory
MAL-2026-18334
Source
OpenSSF Malicious Packages via OSV
Summary
Malicious code in postcss-semantic-themes (npm)
Details
The package advertises itself as a zero-runtime CSS theming kit but on require/import executes a chain of obfuscated JavaScript modules. lib.mjs imports tokens.mjs, which top-level imports cache-warm.mjs — a ~279KB single-line file consisting of a hex-named string array of XOR/base64-encoded blobs decoded at runtime. Three additional sibling modules of the same shape (build-cache.mjs ~203KB, cache-sweep.mjs ~295KB, workspaces.js ~290KB) are shipped and listed in the published files manifest. Alongside the JavaScript loader, the tarball bundles prebuilt N-API native binaries at native/{linux,darwin,win32}/{arm64,x64}/cache-probe.node whose exported symbols implement extensive hypervisor, container, and sandbox detection (VMDetect/VMDetector classes, hypervisor_bit, qemu_fw_cfg, systemd_virt, dockerenv, bluestacks, vbox_module, podman_file, wsl_proc_subdir, amd_sev_msr, azure, chassis_vendor, mac_address_check, is_x86_process_on_arm). None of this has any role in CSS custom-property emission. The README instructs installation as `npm install -D tailwindcss@npm:postcss-semantic-themes`, aliasing the legitimate tailwindcss name onto this package so existing `import 'tailwindcss'` call sites resolve to the obfuscated loader. The combination of an import-time obfuscated loader, multiple additional staged obfuscated payloads, environment-fingerprinting native code to gate execution to non-analyst hosts, and a brandjacking install instruction is the structural shape of a staged supply-chain payload rather than a theming plugin.
## Source: ghsa-malware (d188bb5d3c330ed5c438865b3787cca124861eefe2c8e094e58511bbca437e09) Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.
References
Independent scan evidence
public snapshotBehavioral surface
CryptoDynamicRequireEvalFilesystem
HighEntropyStringsMinifiedObfuscatedUrlStrings
Source & flagged code
3 flaggedlib.cjsView file
4'use strict';
L5: const upstream = require('./vendor/tailwindcss/dist/lib.js');
L6:
Medium
native/linux/x64/cache-probe.nodeView file
•path = native/linux/x64/cache-probe.node
kind = native_binary
sizeBytes = 311880
magicHex = [redacted]
Medium
Ships Native Binary
Package ships native binary artifacts.
native/linux/x64/cache-probe.nodeView on unpkgbase.cssView file
•stage = ast_semantic_analysis; reason = ast_parse_error; limitedFiles = 6
Findings
2 High3 Medium4 Low
HighObfuscated
HighSemantic Analysis Limitedbase.css
MediumDynamic Requirelib.cjs
MediumShips Native Binarynative/linux/x64/cache-probe.node
MediumStructural Risk Force Deep Review
LowEval
LowFilesystem
LowHigh Entropy Strings
LowUrl Strings
Affected versions and remediation
This report applies to postcss-semantic-themes@1.0.0.
See all versions of postcss-semantic-themes for other recorded verdicts.
- Avoid installing postcss-semantic-themes@1.0.0. Remove it from direct dependencies and check your lockfile for transitive copies.
- Choose an independently verified alternative or release. This report does not establish that other versions are safe.
- If this version ran, investigate the affected machine and build environment. Rotate credentials it could access and rebuild from a trusted environment.
Evidence last updated: .
Source advisory published: .
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