Win.Downloader.Nemucod-6769668-0 PDF malware analysis — malicious · 6d7b5355ef81e72c

MALICIOUS

PDF

37.9 KB Authoring application: PyPDF2

MD5: 204f807bb82fa9dc7b164dc0a6338d5b SHA-1: 68b8193cc02509104706a83197cd5db070acb302 SHA-256: 6d7b5355ef81e72c636a7ab4338955045a801133c563605f8ecef1a9ca6b963c

294 Risk Score

Malware Insights

Win.Downloader.Nemucod-6769668-0 · confidence 95%

MITRE ATT&CK

T1059.007 JavaScript T1203 Exploitation for Client Execution T1566.001 Spearphishing Attachment

The PDF file contains obfuscated JavaScript that utilizes ActiveX objects to download and execute a second-stage payload. Heuristics indicate this is a known downloader, specifically identified by ClamAV as Win.Downloader.Nemucod-6769668-0. The JavaScript's functionality of downloading and executing external content is a critical part of its malicious operation.

Machine Learning

Nyx PDF Classifier malicious score 0.9998

Heuristics 8

PDF JavaScript exploit cluster critical PDF_JS_EXPLOIT_CLUSTER

PDF combines an executable JavaScript/action surface with exploit staging indicators such as eval/unescape/fromCharCode, XFA script content, or a related CVE pattern. Benign form JavaScript remains low-severity, but this correlated cluster is high-confidence malicious behavior.
ClamAV: Win.Downloader.Nemucod-6769668-0 critical CLAMAV_DETECTION

ClamAV detected this file as malware: Win.Downloader.Nemucod-6769668-0
eval() call high PDF_EVAL

eval() found — commonly used for obfuscated exploit execution
PDF JavaScript ActiveX downloader high PDF_JS_ACTIVEX_DOWNLOADER

Decoded PDF JavaScript instantiates Windows ActiveX/COM objects to download a payload over HTTP, write it through ADODB.Stream, and execute it through WScript.Shell/rundll32-style process launch. This is commodity downloader behavior rather than a specific Acrobat CVE trigger.
Suspicious extracted artifact high EXTRACTED_FILE_STATIC_TRIAGE

One or more files extracted from inside this sample matched static suspicious-content checks such as script obfuscation, encoded payload blobs, packed data, or execution/download terms.
JavaScript action low PDF_JAVASCRIPT

PDF contains a /JavaScript action. Generic JavaScript is common in benign forms; specific dangerous APIs are scored by separate rules.
Embedded JS stream low PDF_JS

PDF references a /JS stream. Generic JavaScript is common in benign forms; specific dangerous APIs are scored by separate rules.
String.fromCharCode low PDF_FROMCHARCODE

String.fromCharCode found — used to construct payload strings dynamically. Common in benign JavaScript libraries for codepoint manipulation, so this alone is informational; weaponised use is also caught by the dedicated fromCharCode-stage and exploit-shape rules.

Extracted artifacts 3

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`javascript_obj0010_000.js` `dad786a5da7a9423bd46bc59485c30d51abc2ead0d76ea0a704f9b66c97691fc`	pdf-javascript-stream	PDF /JS object 10 at offset 0x479	13453 bytes
Detection ClamAV: No threats found Obfuscation or payload: likely Carved artifact contains 4 eval/decoder/string-building token(s). Carved artifact contains 2 long base64-like blob(s).
`javascript_obj0010_001.js` `8300aef903e7295b2860a9bba8ad23828e2c3a96b4065c1abe2b54df7f62450f`	pdf-javascript-stream	PDF /JS object 10 at offset 0x479	7783 bytes
Detection ClamAV: No threats found Obfuscation or payload: likely Carved artifact contains 2 long base64-like blob(s).
`acroform_b64_00.js` `a7132ec71d3510814e863e1380172dfc7fbf035bd25b7ba6ab73f2bfa2adf99c`	deobfuscated-js	PDF AcroForm base64 (raw) at offset 0x703	5327 bytes
Detection ClamAV: No threats found Obfuscation or payload: likely Carved artifact contains 2 shell/COM execution token(s). Carved artifact contains 1 eval/decoder/string-building token(s).

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