Didier Stevens

This is a Python 3 bug fix version for pecheck.py, a tool to analyze PE files.

pecheck-v0_7_9.zip (https)
MD5: F69709C475D513A8D2031C21EEC13284
SHA256: 99E71A9FC917BB27CDD893F14AE77F2E810A4C7BB56A6E975BB619C978B12D47

In this new version of hash.py, a tool to calculate hashes, I add “hash” checksum8.

Checksum8 calculates the sum of all bytes contained in the provided file(s), each byte is interpreted as an unsigned, 8-bit integer.

I recently had to validate that the path of a URL was a “valid” Meterpreter identifier. When the least significant byte of the 8-bit checksum of the path is equal to 92 (0x5C), then we have a valid URL for a Windows Meterpreter stager.

Take this URL: http://127.0.0.1/RVdP. Could this be a “Windows Meterpreter” URL? Let’s calculate the checksum of RVdP:

The 8-bit checksum of RVdP is 0x015C. The least significant byte is 0x5C, or 92: this matches URI_CHECKSUM_INITW, e.g. this could indeed be a URL used by a reverse http Meterpreter payload.

Besides this new feature, hash.py comes with other features like “pack expressions” and various bug fixes.

hash_V0_0_8.zip (https)
MD5: 03F928332874447F6198A9FDE46E3AA7
SHA256: 80C493639CA7160D1455FABA38A2A04556240326D4BA78B8207CA8FF8B09E1B2

As announced in my previous blog post, this new version of format-bytes.py adds a pack expression (#p#) and other features and (Python 3) bug fixes.

A pack expression is another “here filename”, like #h# for hexadecimal data (which now accepts spaces too).

When format-bytes.py is given a filename as argument, the content of that file is read and processed.

File arguments that start with character # have special meaning. These are not processed as actual files on disk (except when option –literalfilenames is used), but as file arguments that specify how to “generate” the file content. Generating the file content with a # file argument means that the file content is not read from disk, but generated in memory based on the characteristics provided via the file argument. For example, file argument #ABCDE specifies a file containing exactly 5 bytes: ASCII characters A, B, C, D and E.

File arguments that start with #p# are a notational convention to pack a Python expression to generate data (using Python module struct): a “pack expression”.
The string after #p# must contain 2 expressions separated by a # character, like #p#I#123456.
The first expression (I in this example) is the format string for the Python struct.pack function, and the second expression (123456 in this example) is a Python expression that needs to be packed by struct.pack.
In this example, format string I represents an unsigned, 32-bit, little-endian integer, and thus #p#I#123456 generates byte sequence 40E20100 (hexadecimal).
Remark that the Python expression is evaluated with Python’s eval function: this can be abused to achieve arbitrary code execution. Don’t use this in a situation where you have no control over arguments.

I introduced “pack expressions” because I had an IPv4 number represented as a decimal integer, and I needed the dotted quad representation. format-bytes.py will represent 4 bytes as a dotted quad, but I still had to convert a decimal integer to 4 bytes. Hence the introduction of pack expressions (#p#).

For example, number 3232235786 is IPv4 address 192.168.1.10.

Pack expression #p#>I#3232235786 converts number 3232235786 to 4 bytes: >I is the struct format specifier for a big-endian, unsigned 32-bit integer. Remark that I enclose this pack expression in double-quotes (“), as most shells will interpret character > as file redirection if not escaped.

Because of CVE-2020-0601, I also introduced Object Identifier aka OID (DER) decoding. In DER encoding, an OID starts with byte 6 (excluding flags) followed by one byte indicating the length of the bytes representing the OID.

Hexadecimal sequence “06 07 2a 86 48 ce 3d 01 01” is the DER value for OID 1.2.840.10045.1.1.

I also added support for environment variable DSS_DEFAULT_HASH_ALGORITHMS to let you choose your favorite hashing algorithm, in case it is no longer MD5 🙂 .

And last, some (Python 3) bug fixes.

format-bytes_V0_0_11.zip (https)
MD5: D73D5FA410F882F03176CF5FD3E0D90A
SHA256: 34B37CA4E45E4EF0F36F5460CAD429343C0AE993297C104AA8A29C2EE4E7904F

Some bug fixes and new features (pack expression #p# and spaces allowed for #h#), to be covered in more detail in the next blog post on format-bytes.py.

cut-bytes_V0_0_11.zip (https)
MD5: 51F90BBBDE845DEC3EAB94FD30AFCF9B
SHA256: C805CBD23E09D80EB2AF39F8F940CC9188EF7F6B27197D018DA95093AC5D0932

This new version of zipdump.py, a tool to analyze ZIP files, adds option -f to scan for PK records and adds support for Python 3.

More details in an upcoming blog post.

zipdump_v0_0_16.zip (https)
MD5: 616654BDAFFDA1DDE074E6D1A41E8A42
SHA256: F3B6D52BA32D6BA3836D0919F2BBC262F043EF6E26D173DD0965735D4F3B5598

This new version of oledump.py adds support for Python 3. Several plugins and decoders were also updated for Python 3.

There’s a new option to include storages in the overview: –storages.

And option –decompress now does also VBA decompression (it was zlib only). This helps to decompress the dir stream of documents with VBA macros:

And I added type 1009 to plugin_msg.py: Compressed RTF.

oledump_V0_0_43.zip (https)
MD5: F98A06CED73C4FC2CA153B7E751746B5
SHA256: 4FE1DBAB822CEC2489328CE3D4D272400F23F1FAD266C9D89B49D9F83F3AA27F

This is just a bugfix version (Python 3).

numbers-to-string_v0_0_9.zip (https)
MD5: C5629F102FCF58E5CFF24472D35AFF22
SHA256: 5B1CA43EDFD7BA66CF44FB552BD7882AEB13A8765017F9F865071E187410EE63