Win.Downloader.Nemucod PDF malware analysis — malicious · 1f7a0d4936c65af7

MALICIOUS

PDF

299.8 KB Authoring application: PyPDF2

MD5: 5874c1fc9d6c1736a2f2aa0a75008e18 SHA-1: 847598e1b03ce9748a0555c76e1ae1bceabfaf14 SHA-256: 1f7a0d4936c65af75fab620de3132e590e9afc852e02fbb97558ce4e60aeb482

402 Risk Score

Malware Insights

Win.Downloader.Nemucod · confidence 95%

MITRE ATT&CK

T1059.001 PowerShell T1105 Ingress Tool Transfer

This PDF file contains heavily obfuscated JavaScript, flagged by multiple heuristics including PDF_JS_EXPLOIT_CLUSTER and PDF_JS_ACTIVEX_DOWNLOADER. The ClamAV detection 'Win.Downloader.Nemucod-6769668-0' strongly suggests this family. The JavaScript appears to be responsible for downloading and executing a secondary payload, a common characteristic of Nemucod downloaders.

Machine Learning

Nyx PDF Classifier malicious score 0.9797

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_obj0008_000.js` `2407d11eaca81a9c000c4118bd814595eb395912aee25e8cd44c76ae348a938a`	pdf-javascript-stream	PDF /JS object 8 at offset 0x74C	13200 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_obj0008_001.js` `cd8208b9051688ddeb8dd1adae1bd15c41dc6f3f2583106df04bf161ba2a0263`	pdf-javascript-stream	PDF /JS object 8 at offset 0x74C	7237 bytes
Detection ClamAV: No threats found Obfuscation or payload: likely Carved artifact contains 1 long base64-like blob(s).
`acroform_b64_00.js` `a7132ec71d3510814e863e1380172dfc7fbf035bd25b7ba6ab73f2bfa2adf99c`	deobfuscated-js	PDF AcroForm base64 (raw) at offset 0x7AA	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_00004d46.bin` `05073cf1d2daeafbf09a6694077d8a0a460f120090396b7ea19fd69791517f1b`	pdf-embedded-script	PDF decompressed stream script payload at offset 0x4D46	306998 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 10 long base64-like blob(s).

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