Post

TFC CTF 2023 - SOME TRAFFIC

Description

  • Category: Forensic

Our SOC analysts said that in the last few days, some of our employees started to upload a lot of photos on random sites. Check it out.

Flag Format: TFCCTF{…}.

Disclaimer (forensics+stegano)

Download:

Resolution

We have the file sus.pcapng1 which contains network packet capture.

The challenge talks about photos being uploaded on random sites. So let’s find those images using the filter functionality in Wireshark (CTRL+F):

Finding images

We found 3 PNGs and we export them (File -> Export Objects -> HTTP and Content-Typ: multipart/form-data for images only):

Exporting images

Now we have 3 “partial” PNGs because we still need to remove the form data boundaries (here with ImHex):

Removing top

Removing bottom

After we fix those 3 images, we can use steganography tools to find hidden data.

  • We first used stegoVeritas to find any information in transformed images (LSB, RGB) but we cound not find any useful information;
  • Then we used zsteg to detect any stegano-hidden and we found something interesting:

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    $ zsteg -a 1.png 
    imagedata           .. file: MacBinary, Mon Feb  6 07:28:16 2040 INVALID date, modified Mon Feb  6 07:28:16 2040 "F"
    ...
    b4,g,msb,yx         .. file: OpenPGP Public Key
    b8,g,lsb,yx         .. text: "FCCTF{H1dd3n_d4t4_1n_p1x3ls_i5n't_f4n_4nd_e4sy_to_f1nd!}TFCCTF{H1dd3n_d4t4_1n_p1x3ls_i5n't_f4n_4nd_e4sy_to_f1nd!}TFCCTF{H1dd3n_d4t4_1n_p1x3ls_i5n't_f4n_4nd_e4sy_to_f1nd!}TFCCTF{H1dd3n_d4t4_1n_p1x3ls_i5n't_f4n_4nd_e4sy_to_f1nd!}TFCCTF{H1dd3n_d4t4_1n_p1x3ls_"
    ...
    

And this time we get the flag: TFCCTF{H1dd3n_d4t4_1n_p1x3ls_i5n't_f4n_4nd_e4sy_to_f1nd!}.

Additional resources

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