Malicious RTF — malware analysis report

Static analysis result for SHA-256 5238f8d8c3d16b52…

MALICIOUS

RTF

982.7 KB First seen: 2020-01-07
MD5: 4642e8712c8ada8d56bd36416abb4808 SHA-1: a707de5a277573b8080e2147bd99ec1015cf56c5 SHA-256: 5238f8d8c3d16b52d39aa722daff663a5e6307c4b46e360969d84bf409a2690f
380 Risk Score

Malware Insights

MITRE ATT&CK
T1203 Exploitation for Client Execution T1566.001 Spearphishing Attachment

The RTF document contains multiple indicators of exploitation targeting Microsoft Equation Editor, specifically leveraging CVE-2017-11882 and CVE-2018-0798. The presence of large amounts of hex-encoded data within OLE object sections suggests the embedding of a malicious payload. ClamAV detection as Rtf.Dropper.Agent-6899810-0 further confirms its malicious nature as a dropper.

Heuristics 9

  • Equation Editor CLSID critical CVE likely RTF_EQUATION_EDITOR
    Equation Editor OLE CLSID found inside an OLE object — exploited by CVE-2017-11882 / CVE-2018-0802 / CVE-2018-0798
  • CVE-2018-0798 — Equation Editor Matrix record overflow critical CVE exact CVE_2018_0798
    RTF contains hex-encoded MTEF Matrix record exploit signature (NOP-sled 0x60 + padding 0x61 + return address 0x0BFB). CVE-2018-0798 exploits a stack buffer overflow in EQNEDT32.EXE's Matrix record parser and affected Equation Editor broadly, including builds patched for CVE-2017-11882. Widely used by APT groups (Conimes, KeyBoy, Emissary Panda, Rancor).
  • Equation Editor activation — CVE-2017-11882 related high CVE related CVE_2017_11882_ACTIVATION_RELATED
    RTF decodes to an Equation.3 ProgID and requests OLE activation with \objemb plus \objupdate. This reaches the legacy Equation Editor attack surface used by CVE-2017-11882/CVE-2018-0802 documents, but the malformed MTEF/native payload needed for stronger attribution was not recovered.
  • ClamAV: Rtf.Dropper.Agent-6899810-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Rtf.Dropper.Agent-6899810-0
  • \objupdate forces OLE activation high RTF_OBJUPDATE
    RTF contains \objupdate — forces automatic OLE object instantiation when the document is opened, bypassing user interaction. Almost exclusively seen in Equation Editor exploit documents.
  • Package object class high RTF_OBJCLASS_PACKAGE
    OLE Package object — can wrap arbitrary files
  • Large hex data blocks in OLE object high RTF_EXCESSIVE_HEX
    RTF contains ~1005KB of hex-encoded data inside \objdata sections — may hide a payload
  • OLE object data medium RTF_OBJDATA
    RTF contains 3 \objdata section(s) — embedded OLE objects
  • Embedded OLE object medium RTF_OBJEMB
    RTF contains \objemb — embedded OLE object

Extracted artifacts 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
objdata_00_off00000313.bin rtf-objdata-decoded RTF \objdata at offset 0x313 490736 bytes
SHA-256: f947e45aa305ab7dc73b2af1a2f3733ddf12c11416b1accec68622f814945344
objdata_01_off000efd29.bin rtf-objdata-decoded RTF \objdata at offset 0xEFD29 11842 bytes
SHA-256: 82a0e9d2b46fe974ae1d3298ffd405eb8e6ea8fda7665fef57d4e0d76c604d9d
objdata_02_off000efd3b.bin rtf-objdata-decoded RTF \objdata at offset 0xEFD3B 35 bytes
SHA-256: d0771b17e6418e479f528fc4aa124822669975a78f8dc3e35cdc4b0f7c212c4e

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