Malicious Office (OLE) / .XLS — malware analysis report

Static analysis result for SHA-256 cb8fb42b51c97600…

MALICIOUS

Office (OLE) / .XLS

52.5 KB Created: 1996-12-17 01:32:42 Authoring application: Microsoft Excel First seen: 2026-05-11
MD5: 9107a62e4cc5ecdedc718e104a747f27 SHA-1: 08082325ad87186283ace483e85041029a858d45 SHA-256: cb8fb42b51c97600388517b29f73176161244e1e8158126580f571fff7ae2435
100 Risk Score

Malware Insights

The primary indicator of suspicion is the OLE_SLACK_ANOMALY heuristic, which flags a significant portion of the file as unaccounted-for slack space. This often indicates attempts to hide malicious code or data within the file structure. No VBA macros could be extracted due to an unsupported format, limiting further analysis of embedded scripts. The file's content is minimal, consisting only of 'Sheet1', providing no contextual clues. Therefore, the exact attack pattern and family remain unclear, but the slack space anomaly points towards a deliberately obscured malicious file.

Heuristics 2

  • CVE-2009-3129 — Excel FEATHEADER record overflow critical CVE exact CVE_2009_3129
    Workbook BIFF stream contains a FEATHEADER (Feature Header) record with anomalous size (record_size=23, isf=2, cbHdrData=4294967295). Legitimate FEATHEADER records are tiny (<100 bytes) and carry cbHdrData values that fit in the record body; the value here is the documented CVE-2009-3129 exploit primitive — cbHdrData drives a memcpy with attacker-controlled size, leading to memory corruption and code execution in Excel 2007/2003.
  • OLE document has large unaccounted-for region high OLE_SLACK_ANOMALY
    OLE file is 53,783 bytes but its declared streams total only 24,565 bytes — 29,218 bytes (54%) live in unallocated sector slack. This is the canonical hiding place for pre-macro-era Office exploit payloads (XOR-encoded shellcode reached via a parser pointer-corruption bug in the document structure).