Didier Stevens

Saturday 30 April 2022

Quickpost: Machine Code Infinite Loop

Filed under: Reverse Engineering — Didier Stevens @ 8:04

Someone asked me what the byte sequence is for an infinite loop in x86 machine code (it’s something you could use while debugging, for example).

That byte sequence is just 2 bytes long: EB FE.

It’s something you can check with nasm, for example.

File jump-infinite-loop.asm:

BITS 32

loop1:
    jmp loop1
loop2:
    jmp short loop2
    jmp $
    jmp short $
    jmp short -2

nasm jump-infinite-loop.asm -l jump-infinite-loop.lst

File jump-infinite-loop.lst:

     1                                  BITS 32
     2                                  
     3                                  loop1:
     4 00000000 EBFE                        jmp loop1
     5                                  loop2:
     6 00000002 EBFE                        jmp short loop2
     7 00000004 EBFE                        jmp $
     8 00000006 EBFE                        jmp short $
     9 00000008 EB(FE)                      jmp short -2

Quickpost info

Friday 29 April 2022

Update: oledump.py Version 0.0.65

Filed under: My Software,Update — Didier Stevens @ 9:05

This new version of oledump.py brings a new plugin (plugin_metadata) and Python 3 fixes for 2 plugins (plugin_msi and plugin_ppt).

The new plugin is actually an old unpublished plugin, that I updated recently.

This plugin parses Office document metadata as defined in document [MS-OLEPS].

I started to write this in 2015 to parse the metadata of Word documents, but soon I figured out that this functionality was already present in olefile, and I introduced option -M to call this functionality.

But recently, I had to parse metadata that isn’t (yet) parsed by olefile, so I updated and released plugin_metadata.

oledump_V0_0_65.zip (http)
MD5: 319894D211E0C6F41DCEBD5DBBBE3D33
SHA256: 35786C01AC74BE8604E96B528B7EB8EEFBB0D63407D3C78CC31D058528EF20D7

Saturday 23 April 2022

Update: re-search.py Version 0.0.19

Filed under: My Software,Update — Didier Stevens @ 8:47

This is a Python3 stdin fix for re-search.py, my tool to search with regular expressions.

re-search_V0_0_19.zip (http)
MD5: 4007A3E5540871221B55591B50E2239B
SHA256: 263236ABE75B93F1F999474D690A9EB2575EBE42CED8F369FF98B349A5116D11

Monday 18 April 2022

New Tool: pngdump.py (Beta)

Filed under: Announcement,My Software — Didier Stevens @ 7:11

Here is a new tool I’m releasing as beta: pngdump.py.

It’s a tool to analyze PNG files. Unlike jpegdump, you can not yet select items for further analysis.

Sunday 17 April 2022

Update: 1768.py Version 0.0.13

Filed under: My Software,Update — Didier Stevens @ 15:51

This new version of 1768.py brings option -H to include file hashes, introduces shellcode type detection and has updated statistics.

1768_v0_0_13.zip (http)
MD5: F7E85586045AA76C573E010E6FF5F701
SHA256: 33B43A5AB059556C17083E824D407891CD14544B5CA416223020076C5878D310

Saturday 16 April 2022

Update: cut-bytes.py Version 0.0.14

Filed under: My Software,Update — Didier Stevens @ 8:10

This new version of cut-bytes.py adds access to the read data for Python expressions in prefix and suffix options.

cut-bytes_V0_0_14.zip (http)
MD5: EC3434DAAEE06C6F35BD57B77F86833F
SHA256: BCCCE7A73C921BD2CC195155A3A709FBAD7ADC0A267288A4F7F58695A2F103D1

Saturday 9 April 2022

New Tool: myjson-filter.py

Filed under: Announcement,My Software — Didier Stevens @ 8:50

A couple of my tools can produce JSON output, using my own format (myjson).

This output can then be piped into another tool, like strings.py or file-magic.py.

I’m now releasing a tool that can be put into a command pipe to filter the JSON data: myjson-filter.py

For example, here I use myjson-filter.py to remove all items that are XML files (based on the content: starting with <?xml) before strings are extracted with strings.py:

More info in this ISC diary entry I wrote: “Method For String Extraction Filtering“.

myjson-filter_V0_0_2.zip (http)
MD5: 15DDC15DE65F447CE6DA94F8B34C5066
SHA256: EB330FE49421A13A8743F18064788DC2E8189A9B63FD19D517F0B830D1569321

Monday 4 April 2022

.ISO Files With Office Maldocs & Protected View in Office 2019 and 2021

Filed under: maldoc,Malware,Uncategorized — Didier Stevens @ 0:00

We have seen ISO files being used to deliver malicious documents via email. There are different variants of this attack.

One of the reasons to do this, is to evade “mark-of-web propagation”.

When a file (attached to an email, or downloaded from the Internet) is saved to disk on a Windows system, Microsoft applications will mark this file as coming from the Internet. This is done with a ZoneIdentifier Alternate Data Stream (like a “mark-of-web”).

When a Microsoft Office application, like Word, opens a document with a ZoneIdentifier ADS, the document is opened in Protected View (e.g., sandboxed).

But when an Office document is stored inside an ISO file, and that ISO has a ZoneIdentifier ADS, then Word will not open the document in Protected View. That is something I observed 5 years ago.

But this has changed recently. When exactly, I don’t know (update: August 2021).

But when I open an Office document stored inside an ISO file marked with a ZoneIdentifier ADS, Office 2021 will open the document in protected view:

With an unpatched version of Office 2019, that I installed a year ago, that same file is not opened in Protected View:

After updating Office:

Word’s behavior has changed:

The file is now opened in Protected View.

If you want to test this yourself, you can use my ZoneIdentifier tool to easily settings a “mark-of-web” without having to download your test file from the Internet:

Or you can just add the ZoneIdentifier ADS with notepad.

I did the same test with Office 2016, I updated an old version and: the document is not opened in Protected View.

I don’t know exactly when Microsoft Office 2019 was updated so that it would open documents in Protected View when they are inside an ISO file marked as originating from the Internet. But if you do know, please post a comment.

Update: this change happened in August 2021. See comments below. Thanks Philippe.

Sunday 3 April 2022

Power Consumption Of A Philips Hue lamp In Off State

Filed under: Hardware,technology — Didier Stevens @ 17:25

A Philips Hue lamp is a LED lamp that can be controlled wirelessly. It always draws power for its control circuitry, also when the LED is turned off.

I wondered how much power it consumes in the off state. Doing some research, I found a couple of forums where people asked the same question, and getting answers that is was very little, varying from 0,01 A to 0,02 A.

I got similar results for the current when I measured this:

Figure 1: Switched off Philips Hue drawing 0,0175 A (varying easily with 25%)

But I wanted a more precise answer, and not only the current. I am more interested in the power (Watt) consumption. As our domestic electricity meters measure real power over a period of time.

Thus I measured the power consumption of a 1100 Lumen color Philips Hue lamp that I had switched of via the smartphone app over a period of 10 days.

Figure 2: Test setup

And these are the numbers I got after 10 days:

Figure 3: After 10 days of operation in the off state

0,07756 kWh over a period of 10 days, that’s 0,32316 W. Notice that the display indicates KWh, but that should be kWh (lowercase k for kilo).

Extrapolating to a whole year, that’s 2,831 kWh. Which in my case, correspond to a cost of €1,50 (roughly speaking) per lamp per year.

With online numbers claiming the current to be between 0,01 A and 0,02 A, at first I expected the power consumption to be higher. But the power factor is quite low (around 0,10), explaining a lower power consumption.

Friday 1 April 2022

Overview of Content Published in March

Filed under: Announcement — Didier Stevens @ 0:00
Here is an overview of content I published in March:

Blog posts: YouTube videos: Videoblog posts: SANS ISC Diary entries: NVISO blog posts: NVISO Videos:

Blog at WordPress.com.