Malicious RTF — malware analysis report

Static analysis result for SHA-256 81c733c0bae854e2…

MALICIOUS

RTF

2.02 MB Created: 2018-01-02 19:02:00 Authoring application: WPS Office First seen: 2019-01-12
MD5: 643927925bc2e4ad42b0b11221e8053a SHA-1: 19dd82390d82b670e6a77a5fd0d119aab9799d64 SHA-256: 81c733c0bae854e280d0d3c2e7ff1fdcd0f1eef2a653286a641437dcea21f409
342 Risk Score

Malware Insights

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

The RTF document contains multiple critical heuristic firings indicating the exploitation of the Equation Editor vulnerability. It embeds a large amount of hex-encoded data, which upon decoding, reveals a PE header and is identified by ClamAV as Win.Malware.BHRat-9974796-0. This suggests the document is designed to deliver a second-stage payload, likely a RAT, through an embedded OLE object.

Heuristics 8

  • Split hex Equation Editor ProgID + OLE object critical CVE likely RTF_EQUATION_EDITOR
    RTF embeds the Equation.3 ProgID as hex bytes near OLE object activation and splits the byte stream with whitespace or an ignorable RTF group. This is an Equation Editor OLE activation surface commonly used by CVE-2017-11882 / CVE-2018-0802 exploit documents.
  • PE header (with DOS stub) in hex data critical RTF_MZ_HEX
    Hex-encoded PE (MZ + DOS stub) found inside RTF — likely an embedded executable payload
  • \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.
  • Large hex data blocks in OLE object high RTF_EXCESSIVE_HEX
    RTF contains ~1996KB of hex-encoded data inside \objdata sections — may hide a payload
  • 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.
  • 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
  • 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://crl.trustasia.com/codesha2.crl0A In RTF body
    • http://aia.trustasia.com/codesha2.cer0In RTF body
    • http://crl.trustasia.com/ca.crl0In RTF body
    • http://aia.trustasia.com/ca.cer0In RTF body
    • http://crl.globalsign.net/Root.crl0In RTF body
    • http://www.globalsign.net/repository/03In RTF body
    • http://crl.globalsign.net/root.crl0In RTF body
    • http://crl.globalsign.net/Timestamping1.crl0In RTF body
    • http://www.globalsign.net/repository/0In RTF body
    • http://secure.globalsign.net/cacert/ObjectSign.crt09In RTF body
    • http://crl.globalsign.net/ObjectSign.crl0In RTF body
    • http://www.globalsign.net/repository09In RTF body
    • http://crl.globalsign.net/primobject.crl0NIn RTF body
    • http://secure.globalsign.net/cacert/PrimObject.crt0In RTF body

Extracted artifacts 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
objdata_00_off00089bb7.bin rtf-objdata-decoded RTF \objdata at offset 0x89BB7 754772 bytes
SHA-256: 24d4862fd51bb29b9887413c843aabfa3da08a791ce8b6aaf0eab551648ea0c6
Detection
ClamAV: Win.Malware.BHRat-9974796-0
Obfuscation or payload: likely
Static shellcode analysis recovered command string(s): cmd.exe /c Carved artifact entropy is 7.49, consistent with packed or encrypted content.
objdata_01_off001fa4b0.bin rtf-objdata-decoded RTF \objdata at offset 0x1FA4B0 10550 bytes
SHA-256: 4bd137e8edff0e29a954f4346ce829c1213ed122ac58050013837c739f39785a
objdata_02_off001ff76d.bin rtf-objdata-decoded RTF \objdata at offset 0x1FF76D 10550 bytes
SHA-256: d93402785796c448b40d9b4559c5aed95a2825a205b32e9b766bb7884b44de33

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