Forensic Blogs

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New Tool: msoffcrypto-crack.py

This is a new tool to recover the password of encrypted MS Office documents. I quickly put together this script to help with the analysis of encrypted, malicious documents.

This tool relies completely on Python module msoffcrypto to decrypt MS Office documents.

Since this is a Python tool based on a Python library, don’t except fast password recovery. This is more a convenience program.

It can recover passwords using a build-in password list, or you can provide your own list via option -p.

The tool can also decrypt the encrypted MS Office document if the password is recovered: used option -o to achieve this. Otherwise, the tool just displays the recovered password.

Like many of my tools, it can take its input from stdin and provide the decrypted document via stdout.

It’s developed with Python 2, and also tested on Python 3.

Read the man page for all the details: option -m.

msoffcrypto-crack_V0_0_1.zip (https)
MD5: F67060E0DE62727A1A69D0FD6F39013A
SHA256: 1466B94B56595BA0B91F0A2606F699E1D737E964F3F1A4DFDF7EAA47843DD063

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Analyzing PowerPoint Maldocs with oledump Plugin plugin_ppt

VBA macros inside a PowerPoint document are not stored directly inside streams, but as records in the “PowerPoint Document” stream. I have a plugin to parse the records of the “PowerPoint Document” stream, but I failed to extract the embedded, compressed OLE file with the macros. Until a recent tweet by @AngeAlbertini brought this up again. On his sample too I failed to extract the compressed OLE file, but then I remembered I had fixed a problem with zlib extraction in pdf-parser.py. Taking this code into plugin_ppt.py fixed the decompression problems.

VBA macros in a PowerPoint document do not appear directly in streams:

Plugin plugin_ppt parses records found in stream “PowerPoint Document”:

Each line represents a record, prefixed by an index generated by the plugin (to easily reference records). Records with a C indicator (like 1 and 435) contain sub-records. Records prefixed with ! contain an embedded object.

Record 441 (RT_ExternalOleObjectStg) interests us because it contains an OLE file with VBA macros.

Plugin option -s can be used to select this record:

Plugin option -a can then be used to do an hex/ascii dump:

The first four bytes are the size, and then follows the zlib compressed OLE file (as indicated by 0x78).

This OLE file can be decompressed and extracted with option -e, but pay attention to use option -q (quiet) so that oledump will only report the output of the plugin, and nothing else. This can then be piped into a second instance of oledump:

And now we can extract the VBA macros:

oledump_V0_0_38.zip (https)
MD5: C1D7F71A390497A516F67D798BA25128
SHA256: 4CADEE69D024E9242CDA0CE3A9C22BCB1CAFF9D5BA2D946519C6B7C18F895B81