self-replicating PDF x ELF64 polyglot

[ilya-lyapunov]

Entry Info

• Date: 18 January 2026
• BGGP Challenge: bggp6
• Name: ilya
• Contact Info: ilya:rx.haunted.computer (matrix)
• Online Presence: none
• Writeup Link: github gist

File Info

• Target File Type: ELF (x86_64), PDF
• Target File Size: 512
• SHA256 Hash: b2a9ab69ac017fcb6d568a4ba322d0352699f5648afc69f65db202ff7802a0c2

File Contents

f0VMRgIBAQMAAAAAAAAAAAIAPgABAAAAsABAAAAAAABAAAAAAAAAAAAAAAAAAAAAAAAAAEAAOAAC
AEAAAAAAAAEAAAAFAAAAAAAAAAAAAAAAAEAAAAAAAAAAQAAAAAAA8AAAAAAAAADwAAAAAAAAAAAQ
AAAAAAAAAQAAAAYAAADwAAAAAAAAAPAQQAAAAAAA8BBAAAAAAAAQAQAAAAAAABABAAAAAAAAABAA
AAAAAAC+7QEAAEjHx+4AQAC4VQAAAA8FSMfCAAIAAEjHxgAAQABIice4AQAAAA8FuAMAAAAPBb8G
AAAAuDwAAAAPBTYAJVBERi0xLgoxIDAgb2JqPDwvS2lkc1s8PC9SZXNvdXJjZXM8PD4+L0NvbnRl
bnRzIDIgMCBSL1BhcmVudCAxIDAgUi9UeXBlL1BhZ2UvTWVkaWFCb3hbMCAwIDk5IDk5XT4+XS9U
eXBlL1BhZ2VzL0NvdW50IDE+PmVuZG9iagoyIDAgb2JqPDw+PnN0cmVhbQpCVC8gOSBUZig2KScg
RVQKZW5kc3RyZWFtCmVuZG9iagozIDAgb2JqPDwvVHlwZS9DYXRhbG9nL1BhZ2VzIDEgMCBSPj5l
bmRvYmoKdHJhaWxlcjw8L0luZm88PC9BdXRob3IoQkdHUCk+Pi9Sb290IDMgMCBSPj4KJUVPRgA=

Environment Info

Should run on any x86_64 Linux or Unix. I used fasm to build the executable.

Target Software and Version

Any x86_64 Linux or Unix.

PDF only renders in Firefox, Chrome and Adobe Reader.

Environment Setup

From any x86_64 Linux/Unix system, just run the ELF and it should output another file called 6.

Renaming the file to 6.pdf and opening it in Firefox, Chrome or Adobe Reader will render the number 6.

If you run 6.pdf as an executable, it will make another copy of itself (again called 6).

Additional Info

See writeup for additional info.