Rating:
misc/hidden in plain sheets
burturt
251 solves / 315 points
I found this google sheets link on the internet. I'm sure it's hiding something, but I can't find anything? Can you find the flag?
Choose any link (they're all the same): Link 1 Link 2 Link 3
The link given in the challenge leads to a google sheets project. On first glance this looks pretty boring, but after some digging, I was able to find a protected sheet called flag.
It is marked view only, which I thought would mean it would be possible to view it, but upon clicking it nothing happend. So we found the sheet, but we are not able to open it - interesting...
After that, I decided to look through the Options I had since they were very limited. There wasn't much I could find except the search feature.
On closer inspection of the search feature I found that you could search all sheets, but even better there was an option to search a specific range. The syntax of this seemed to be
sheetname!cell.
Another useful feature is the search using regex, which saved me from a lot of brute forcing. I constructed a regex that would basically be triggered by any character of the flag [!-}]+ which is not the cleanest solution, but it did the job.
Combining these two observations I was able to get any set of characters in any cell of the protected sheet. So the combination of Find: [!-}]+ and Search - Specific Range: flag!A1 resulted in
A match was found in hidden cell flag!A1 with value "l".
Going forward it was just a matter of looking at cells B1, C1, D1, ...
And just like this, we get the flag:
lactf{H1dd3n_&_prOt3cT3D_5h33T5_Ar3_n31th3r}
