Win.Downloader.Nemucod-6769668-0 PDF malware analysis — malicious · 3d7da857b198270c

MALICIOUS

PDF

91.0 KB Authoring application: PyPDF2

MD5: 6f0e5aeeb23f650da9c8998765cc2ccb SHA-1: c66d71c49b1f9eaae6c5c6b8b1d4f45126fbad48 SHA-256: 3d7da857b198270cfafbaca524fd17daebdd07bc1adccc80e41ca9ca8b2d57ef

396 Risk Score

Malware Insights

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

MITRE ATT&CK

T1059.001 PowerShell T1204.002 Malicious File

The PDF contains embedded JavaScript, flagged by multiple high-severity heuristics including PDF_JAVASCRIPT, PDF_JS, PDF_EMBEDDED_SCRIPT_PAYLOAD, and PDF_JS_ACTIVEX_DOWNLOADER. The ML classifier also strongly indicated maliciousness. ClamAV detection confirms this as Win.Downloader.Nemucod-6769668-0. The script's likely intent is to download and execute a second-stage payload, consistent with a downloader's function.

Machine Learning

Nyx PDF Classifier malicious score 0.9962

Heuristics 12

JBIG2 + active content high CVE related PDF_JBIG2_ACTIVE_CONTENT

JBIG2Decode appears with JavaScript/XFA/RichMedia — a related indicator for JBIG2 parser-exploit families including CVE-2021-30860 and CVE-2009-0658, but not a unique CVE fingerprint.
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.
JBIG2Decode filter medium PDF_JBIG2

JBIG2 image decoder present — historically used in zero-click exploits
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.
PDF paints image(s) but contains no text operators info PDF_IMAGE_ONLY_LURE

PDF has 2 image XObject(s) and the content stream contains no text-emitting operators (BT/ET, Tj, TJ, ', ") in either raw bytes or decompressed streams — this is the screenshot-as-PDF pattern used to bypass text-based scanners and to deliver instructions purely through rendered pixels. It is informational unless paired with invisible links or risky URI context.

Extracted artifacts 4

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`javascript_obj0005_000.js` `0c7d8df9bd3559c8bc42d04514b1e762fae5414c5c0681d0d19d3036070b808e`	pdf-javascript-stream	PDF /JS object 5 at offset 0x799	13078 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_obj0005_001.js` `ea5d63a09334abf273a446805c744a9202107756736c60bde633fb6c7db1110f`	pdf-javascript-stream	PDF /JS object 5 at offset 0x799	988 bytes
`acroform_b64_00.js` `0e752bdefadc04c6f26519893dcdd99931d4e21349f5a0ad393239c84ece1678`	deobfuscated-js	PDF AcroForm base64 (raw) at offset 0x18FF	5301 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_00004c84.bin` `8a393a07293efae171effd80a2eb1490a4f7fc0f01fefe5cd8582a3268d1efec`	pdf-embedded-script	PDF decompressed stream script payload at offset 0x4C84	93118 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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