Easter Egg 2

OTW 2019 - Easter egg #2

Solution

The easter egg is visible in a response header on static assets on the CTF site.

$ curl -vv "https://advent2019.overthewire.org/static/img/sponsors/f-secure.png" 
*   Trying 104.28.31.80...
> GET /static/img/sponsors/f-secure.png HTTP/2
> Host: advent2019.overthewire.org
> User-Agent: curl/7.61.0
> 

< HTTP/2 200 
< date: Thu, 05 Dec 2019 19:28:16 GMT
< content-type: image/png
< content-length: 20428
< last-modified: Fri, 01 Nov 2019 06:12:09 GMT
< x-easteregg2: ==QftRHdz8VZydmZuNzXhJ3MxcGMltnSHJkT

Flag

Flag is rot13 as (reversed) base64 in the x-easteregg2 header.

$ alias rot13="tr 'A-Za-z' 'N-ZA-Mn-za-m'"                                      
$ echo -e "==QftRHdz8VZydmZuNzXhJ3MxcGMltnSHJkT" | rev | base64 -d | rot13

AOTW{r0t13en_3aster_3ggz}