Win.Downloader.Nemucod-6769668-0 PDF malware analysis — malicious · 00d703b95f41caa5

MALICIOUS

PDF

173.6 KB Authoring application: PyPDF2

MD5: 1b57d41645e7e3ebfc299705e819a215 SHA-1: 989b1663c6a8d68e4ac0ec8bdcf8eb0b04f62b7e SHA-256: 00d703b95f41caa5c44457578604d2f8bc54bc12166f54f7d259de052388bb1f

402 Risk Score

Malware Insights

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

MITRE ATT&CK

T1059.001 PowerShell T1204.002 Malicious File

This PDF file contains embedded JavaScript that utilizes eval() and String.fromCharCode() functions, indicative of obfuscation and exploit attempts. The JavaScript is designed to act as a downloader, leveraging ActiveX objects to fetch and execute a secondary payload, as suggested by the 'PDF JavaScript ActiveX downloader' heuristic. ClamAV detections further confirm its malicious nature as Win.Downloader.Nemucod.

Machine Learning

Nyx PDF Classifier malicious score 0.9763

Heuristics 11

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
ClamAV detection on extracted artifact critical EXTRACTED_FILE_CLAMAV

ClamAV flagged at least one file extracted from inside this sample. Even when the wrapping document carries no AV detection of its own, a hit on the carved artifact is a strong indicator the sample is a delivery vehicle.
eval() call high PDF_EVAL

eval() found — commonly used for obfuscated exploit execution
Embedded script payload in PDF stream high PDF_EMBEDDED_SCRIPT_PAYLOAD

PDF stream bytes contain script execution markers such as ActiveXObject/CreateObject, WScript.Shell, PowerShell, or shell-exec primitives. This is stronger than ordinary PDF JavaScript because it indicates a staged external script payload hidden in stream bytes.
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.
AcroForm button with action trigger low PDF_ACROFORM_BUTTON

PDF contains a /Btn form field together with a SubmitForm/URI/Launch/JS trigger — this is the building block of fake 'Download' or 'Open' button overlays used in PDF phishing lures

Extracted artifacts 4

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`javascript_obj0011_000.js` `97d6044f031cee4bfaf02695a3a2b3b6ef169a8c04e244a793d7cf6f4bcc8e8b`	pdf-javascript-stream	PDF /JS object 11 at offset 0x5D1	13525 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_obj0011_001.js` `c85a26f0ba215bd4fa21273c88d228cf586c368b7dd1a949e8337ca401113500`	pdf-javascript-stream	PDF /JS object 11 at offset 0x5D1	7784 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 0x85C	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).
`embedded_pdf_script_00004d63.bin` `45d3b53d3b8ef24d28fc1a5a8b99d1f3eb2565ec9c06c988fb0f74ab61da81e0`	pdf-embedded-script	PDF decompressed stream script payload at offset 0x4D63	177755 bytes
Detection ClamAV: Win.Downloader.Nemucod-6769668-0 Obfuscation or payload: likely Carved artifact contains 2 shell/COM execution token(s). Carved artifact contains 12 eval/decoder/string-building token(s). Carved artifact contains 2 long base64-like blob(s).

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