Blame Game | picoCTF 2024 Solutions

Description

Someone's commits seems to be preventing the program from working. Who is it?

Setup

Download the challenge zip, unzip it locally, then change into the drop-in directory.

wget https://artifacts.picoctf.net/c_titan/74/challenge.zip && \ unzip challenge.zip && \ cd drop-in/

Solution

Unlike the Time Machine challenge, the answer isn't visible from a plain git log over the entire repo. You need to focus on message.py to pinpoint the culprit.

Step 1List repository history
Use git log --oneline --decorate to see an overview of commits. This gives context about recent changes and commit messages.
git log --oneline --decorate
Step 2Focus on the suspicious file
Run git log message.py to narrow the search to the file that broke the flag printer. You're interested in the commit introducing the bogus optimization.
git log message.py
Step 3Blame the culprit
Once you've identified the offending commit, take note of the author line; that name is the flag. You can double-check by running git show <COMMIT_HASH>.
git show <COMMIT_HASH>

Flag

picoCTF{@sk_th3_1nt3rn_ea3...}

The flag is the author of the suspicious commit (the "optimize file size of prod code" change in message.py). It appears in the git log message.py output once you examine the file history.