Nemucod PDF malware analysis — malicious · 97587a93b8842f4e

MALICIOUS

PDF

131.4 KB Authoring application: Acrobat040PDFMaker04080561040for040PowerPoint (via PyPDF2)

MD5: facab9d1ba68c680cfc60332067c4bee SHA-1: 3ec03a22e5f565ae98b7cefdc33538de07080087 SHA-256: 97587a93b8842f4e88a295697ad0a1a764bfcb85f75255795804b843f2740806

342 Risk Score

Malware Insights

Nemucod · confidence 95%

MITRE ATT&CK

T1059.001 PowerShell T1204.002 Malicious File T1071.001 Web Protocols

The PDF file contains multiple high-severity heuristic firings related to embedded JavaScript, including ActiveX downloaders and eval() calls, indicating malicious intent. The ML classifier and ClamAV detection strongly support this, identifying the file as Win.Downloader.Nemucod-6769668-0. The embedded JavaScript, particularly the deobfuscated acroform_b64_00.js, likely attempts to download and execute a secondary payload. The presence of a User-Agent string 'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)' within the obfuscated script further supports the downloader functionality.

Machine Learning

Nyx PDF Classifier malicious score 0.9939

Heuristics 10

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.
Optional Content Group with action trigger low PDF_OPTIONAL_CONTENT

Optional Content Group (layer) co-occurs with an action trigger — content can be selectively hidden from viewers or scanners while the action still fires on open

Extracted artifacts 4

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`javascript_obj0083_000.js` `291a545f1f0635fa3a5b4107c46f3d934ff47953e0dcf04c7acf939b6bcb5e2d`	pdf-javascript-stream	PDF /JS object 83 at offset 0x6891	13202 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_obj0083_001.js` `5f51c0aec5fcd0c1622819b5be3e2b043357964617b676275245514efda4120f`	pdf-javascript-stream	PDF /JS object 83 at offset 0x6891	7780 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 0x6B18	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_0000adb9.bin` `66654040e3d113f425c7c5db8fc09e6446ccc45fab7dd8d3a33d91a2ea7a04bf`	pdf-embedded-script	PDF decompressed stream script payload at offset 0xADB9	134570 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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