---
id: "GHSA-fh55-fq5h-h352"
kind: "package"
aliases: ["GHSA-fh55-fq5h-h352", "MAL-2026-18334"]
title: "Malicious code in postcss-semantic-themes (npm)"
severity: "critical"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: [{"name": "postcss-semantic-themes", "fixed": [], "affected": "all versions", "ecosystem": "npm"}]
ecosystems: ["npm"]
tags: ["malicious", "package"]
not_affected_if: []
published_at: "2026-10-26T16:17:58+00:00"
first_seen_at: "2026-10-26T20:51:55+00:00"
updated_at: "2026-10-26T21:05:48+00:00"
sources: [{"source": "osv-malicious", "url": "https://osv.dev/vulnerability/MAL-2026-18334", "first_seen_at": "2026-10-26T20:51:55+00:00"}]
---

# Malicious code in postcss-semantic-themes (npm)

## Affected

- npm:postcss-semantic-themes affected all versions fixed ?

## Timeline

- 2026-10-26T20:51:55+00:00 osv-malicious https://osv.dev/vulnerability/MAL-2026-18334

## From the sources

---
_-= Per source details. Do not edit below this line.=-_

## Source: amazon-inspector (21c91b39929f03c30e501726fc2d1c1fa43f17bf2ed77bda52380e563c1171e0)
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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_