Win.Downloader.Nemucod-6769668-0 PDF malware analysis — malicious · 0302c8e3b3fcf8a2

MALICIOUS

PDF

249.7 KB Authoring application: PyPDF2

MD5: 5401ae1e8ddc21ad7c52f4f9c4a2b6ea SHA-1: a5ed50fa7d193ad404df6f5dc8776319f7730c3a SHA-256: 0302c8e3b3fcf8a239d8069c229918d671c5c457252e34af5d9b2de066c44830

404 Risk Score

Malware Insights

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

MITRE ATT&CK

T1059.007 JavaScript T1203 Exploitation for Client Execution

This PDF file contains embedded JavaScript that utilizes eval() and String.fromCharCode() to deobfuscate and execute malicious code. The script is designed to download and execute a second-stage payload, as indicated by the 'PDF JavaScript ActiveX downloader' heuristic and ClamAV detection of Win.Downloader.Nemucod. The presence of multiple JavaScript streams and exploit cluster signals further supports this assessment.

Machine Learning

Nyx PDF Classifier malicious score 0.9900

Heuristics 12

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
Embedded URL info EMBEDDED_URL

One or more URLs were extracted from the document. The URL itself is not a detection — see the per-URL labels for which channel (macro, JS, link annotation, document body, ...) reached each URL.

URL http://www.adobe.com/acrobat

Extracted artifacts 5

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`javascript_obj0007_000.js` `19884c2c789cc7346682f3837a80731f9b5e9ba31256745c7b8d2482ee5f47b7`	pdf-javascript-stream	PDF /JS object 7 at offset 0x63A	12484 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_obj0007_001.js` `1eb921c5710fadbe780b1b1122fd4bb4e9c484132c30320f92010c0f048e5a02`	pdf-javascript-stream	PDF /JS object 7 at offset 0x63A	7223 bytes
Detection ClamAV: No threats found Obfuscation or payload: likely Carved artifact contains 1 long base64-like blob(s).
`javascript_obj0125_002.js` `6ec6509be655ad55d7f043dd30a57424b3e40e0dcc056cf0d9c53cf4255c07fb`	pdf-javascript-stream	PDF /JS object 125 at offset 0x1FB9B	808 bytes
`acroform_b64_00.js` `4415c8350e1dbdc26c7c65abec85210e5cee0984e800ed64eb8b6883ff8314de`	deobfuscated-js	PDF AcroForm base64 (raw) at offset 0x68E	5323 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_00004685.bin` `46844bbddeca3ff97eb1360b4df689337a1f30e4915bc5a71b142b37121d2e3d`	pdf-embedded-script	PDF decompressed stream script payload at offset 0x4685	255626 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 3 long base64-like blob(s).

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