Summary
Togoder Security scanned the npm package postcss@8.5.23 on Oct 6, 2026. An AI review of 29 source files produced 1 medium, 3 low severity findings. The overall verdict is medium: the findings flag risky but common patterns (dynamic code, unsafe defaults, broad file or network access) rather than confirmed malware.
Findings 4
Path Traversal Risk in Source Map Loading
NPS-30F160823F9F
The loadFile method attempts to restrict loading of source maps to files within the CSS file's directory by checking relative paths. However, the guard is only applied when 'trusted' is false and 'unsafeMap' is not set. In the loadMap method, when 'prev' is a function, loadFile is called with trusted=true, bypassing these checks entirely. If an attacker can control the 'prev' function or its return value (e.g., via a crafted build configuration or plugin), they could load arbitrary files from the filesystem. Additionally, the check uses string operations that may be bypassed with edge cases like symlinks or non-normalized paths.
Prototype manipulation via __proto__ assignment
NPS-17A1E22AD8ED
The hydrateInputs function constructs objects with literal '__proto__' properties: '{ ...input, __proto__: Input.prototype }' and '{ ...inputHydrated.map, __proto__: PreviousMap.prototype }'. While this appears intended to rehydrate class instances from JSON, setting '__proto__' explicitly is widely flagged as a dangerous pattern because it can be abused for prototype pollution. In this specific file the value is a hard-coded library prototype (not attacker-controlled), so it does not directly enable pollution, but it is a fragile and security-sensitive construct worth noting.
Unsafe spread of untrusted JSON into object prototypes
NPS-D1A1817D0529
constructNode does 'let defaults = { ...json }' on data coming from JSON (potentially untrusted input to fromJSON). If any nested property named '__proto__' or 'constructor' is present in the JSON, spread/merge semantics could interact with prototype chains depending on runtime and downstream constructors. This mirrors known prototype-pollution risks in deserialization helpers.
Unsafe Base64 Decoding Fallback to window.atob
NPS-F20379FF7B44
The fromBase64 function uses Buffer.from(str, 'base64').toString() when Buffer is available, but falls back to window.atob(str) otherwise. In Node.js, Buffer is always available, so the fallback is unreachable in server-side contexts. However, if the code is bundled for browser use, window.atob is used. This is not inherently malicious, but the dynamic nature of the fallback and the fact that it decodes inline source maps could be abused if an attacker controls the source map data to cause memory exhaustion or unexpected behavior. The risk is low given typical usage.
Files reviewed
| File | Verdict | What the reviewer saw |
|---|---|---|
| lib/fromJSON.js | medium | No exfiltration, credential harvesting, shell execution, network calls, or install-time hooks were found; the only concerns are the explicit __proto__ assignments during instance rehydration, which are a security-sensitive but hard-coded pattern. |
| lib/previous-map.js | medium | The code is a legitimate source map handling utility with no obvious malicious patterns, but it contains a potential path traversal bypass in its source map loading logic when a trusted previous map function is provided. |
| lib/at-rule.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/comment.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/container.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/css-syntax-error.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/declaration.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/document.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/input.js | safe | No malicious patterns detected; the file is legitimate PostCSS input handling code with no exfiltration, credential harvesting, dynamic execution, or suspicious network/file/process activity. |
| lib/lazy-result.js | safe | No malicious patterns detected; this is a legitimate PostCSS LazyResult implementation with no data exfiltration, credential harvesting, dynamic code execution, or suspicious network/file/process activity. |
| lib/list.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/map-generator.js | safe | The file is a standard PostCSS source map generator with no malicious patterns, network activity, process spawning, obfuscation, or credential access. |
| lib/no-work-result.js | safe | No malicious patterns detected; the file is a standard PostCSS result wrapper with no network, filesystem, process, or dynamic code execution activity. |
| lib/node.js | safe | This is the standard PostCSS Node class implementation with no malicious patterns; it handles CSS AST manipulation, cloning, and serialization without network, filesystem, or process operations. |
| lib/parse.js | safe | No malicious patterns detected |
| lib/parser.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/postcss.js | safe | No malicious patterns detected; the file is a standard PostCSS module entry point with only legitimate requires, exports, and a deprecated plugin helper. |
| lib/postcss.mjs | safe | Cleared by Jev triage; no further analysis needed |
| lib/processor.js | safe | No malicious patterns detected; the code is a standard PostCSS Processor implementation with no data exfiltration, credential harvesting, obfuscation, or dynamic code execution. |
| lib/result.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/root.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/rule.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/stringifier.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/stringify.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/symbols.js | safe | Cleared by Jev triage; no further analysis needed |
Show 4 more files
| File | Verdict | What the reviewer saw |
|---|---|---|
| lib/terminal-highlight.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/tokenize.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/warn-once.js | safe | Cleared by Jev triage; no further analysis needed |
| lib/warning.js | safe | Cleared by Jev triage; no further analysis needed |
Affected version ranges
None of the 2 scanned versions of postcss are flagged high or critical. The latest scanned version, 8.5.28, is medium risk. Only versions we have scanned are listed; unscanned versions between them are not covered.
| Versions | Verdict | Count | Range | Top findings |
|---|---|---|---|---|
| 8.5.28 | Needs review | 1 | 8.5.28 | |
| 8.5.25 | Not scanned | 1 | 8.5.25 | |
| 8.5.23 | Needs review | 1 | 8.5.23 | Path Traversal Risk in Source Map Loading |
| 7.0.39 – 8.4.49 | Not scanned | 3 | >=7.0.39 <=8.4.49 |
Full list, including published versions not scanned yet: version ranges API.
Scanned versions of postcss
Frequently asked questions
Is postcss safe to use?
No confirmed malware was found in postcss@8.5.23, but the review flagged 1 medium, 3 low severity findings for risky patterns worth checking before you rely on it.
Does postcss contain malware?
No malware was identified in postcss@8.5.23 when Togoder Security scanned it on Oct 6, 2026. A new version can still introduce malicious code, so scan the exact versions in your lockfile.
How was postcss checked?
Togoder Security downloaded the published npm package and had an AI model read its 29 source files, looking for install scripts, credential access, network exfiltration, obfuscation, backdoors and crypto-wallet theft. The results are cached by file hash and shown here.
How do I scan postcss together with the rest of my dependencies?
Upload your lockfile at https://security.togoder.click/scan or call the API documented at https://security.togoder.click/api-docs. Files that have already been scanned, like the ones in postcss@8.5.23, cost nothing.