Validator

Challenge

Trust Me, It’s Just a Simple Check

Solution

validator is a Linux PIE binary with obfuscated validation flow. Instead of full deobfuscation, the solve used an in-process oracle.

Approach:

1. Identified internal checker symbol offsets in the binary.
2. Used LD_PRELOAD hook to run inside the target process (so PIE base is already mapped correctly).
3. Resolved runtime base with dl_iterate_phdr.
4. Called the per-character checker function (base + 0x3440) for each position and printable byte.
5. Reconstructed the full accepted string from oracle positives.
6. Verified by piping candidate to the binary and confirming success message.

Recovered flag: VBD{I_kn0w_y0u_w0uld_us3_Opus_hehe_eafa09ad1898e0bcf9c0225076632225}

Flag

VBD{I_kn0w_y0u_w0uld_us3_Opus_hehe_eafa09ad1898e0bcf9c0225076632225}