justCTF 2019 Write-ups

CTF event organized by justCatTheFish team.

Matryoshka

We were provided with below challenge’s description and an image file.

matryoshka.jpg

We checked the file and found it has 4 images inside.

We tried to extract it with binwalk and foremost but failed, so we tried to extract it manually.

We copied the binary of the last image to create as a new file and viewed it.

Based on the output above, the flag for this challenge is justCTF{d1d_y0u_kn0w_7h47_f1r57_m47ry05hk4_d0ll_w45_m4d3_129_y34r5_4g0}

FirmwareUpdater

We were provided with below challenge’s description.

We were asked to upload a zip file. When we upload the zip file, it unzipped it and view file name README.md. Since we had already known that the flag is in /etc/flag. We just created a new README.md as a symlink to /etc/flag then replaced it with the original file, zipped it and uploaded the file. Once it read the file, it will show /etc/flag file instead.

The flag for this challenge is justCTF{A_Fin3_W4y_T0_Upd4t3_m3_y0}

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