33 lines
2.2 KiB
Markdown
33 lines
2.2 KiB
Markdown
|
# Office macro download inspection
|
||
|
|
|
||
|
|
With central YARA enabled, `security.yara.scanOfficeMacros` defaults to true.
|
||
|
|
The contained local scanner matches the same administrator rules against original
|
||
|
|
bytes, unpacked VBA projects, contiguous OLE streams (including compiled data),
|
||
|
|
and decompressed VBA source. It does not execute macros or retain source code.
|
||
|
|
|
||
|
|
Admins can turn this additional extraction off independently of YARA. ICAP remains
|
||
|
|
mandatory when enabled; all enabled scanners must approve the exact downloaded
|
||
|
|
bytes before the browser offers to save them. A matching rule blocks the file.
|
||
|
|
Benign VBA is not blocked simply because a macro exists. Archive, stream, module,
|
||
|
|
code and runtime budgets bound parsing; failures do not become clean results.
|
||
|
|
|
||
|
|
The default incoming document-DLP requirement remains conservative. Office rendered
|
||
|
|
content is not completely classified. To allow incoming Office after malware
|
||
|
|
inspection, an admin can explicitly disable `fileTransfers.download.requireDocumentDlp`
|
||
|
|
in Download inspection and publish the policy. This affects incoming document DLP;
|
||
|
|
upload checks remain enforced. At least one malware scanner is still required.
|
||
|
|
Explicit no-antivirus mode continues to require complete document DLP.
|
||
|
|
|
||
|
|
Supported local extraction targets ordinary VBA projects in OOXML and OLE. XLM,
|
||
|
|
XLSB, encrypted/corrupt projects and embedded Office containers remain unsupported
|
||
|
|
and block when extraction is enabled. Source matching cannot establish source/p-code
|
||
|
|
equivalence or detect every obfuscated macro; ICAP/AV remains a complementary layer.
|
||
|
|
|
||
|
|
A pinned benign XlsxWriter fixture verifies that a source-only YARA marker absent
|
||
|
|
from original ZIP bytes blocks after extraction, while an unmatched benign project
|
||
|
|
allows the malware gate. The same two outcomes are tested inside Windows AppContainer.
|
||
|
|
Dependencies are four curated hash-pinned wheels in requirements-macros.lock.txt;
|
||
|
|
optional p-code/XLM tools are not installed or invoked.
|
||
|
|
|
||
|
|
Extraction follows [olevba's source extraction API](https://github.com/decalage2/oletools/blob/master/oletools/doc/olevba.md)
|
||
|
|
and bounded [MS-OVBA compression](https://learn.microsoft.com/en-us/openspecs/office_file_formats/ms-ovba/ec1bc788-27de-47d9-8db4-6be2b5cff52b).
|