CTF Writeups

Platform HASBL CTF 2026 Difficulty Mixed (Easy → Medium) OS Jeopardy — Forensics (Linux toolchain) Tags QR-code decoding with Reed-Solomon tolerance, JPEG metadata extraction (EXIF, COM, XMP), base64/base32 encoding fingerprints, bit-stream-to-JPEG reconstruction, magic-byte surgical repair, file-header recognition HASBL CTF 2026 is a multi-category jeopardy event with Reverse Engineering, Pwn, Web, and Forensics tracks. This writeup is dedicated to the Forensics track — the five forensics challenges (Quick Response, Logo, Digits, our sweet cat, Pamuk, and The Magic of "Magic Numbers") were all solved, and each one teaches a different file-forensics primitive: QR-code decoding despite a visual overlay, JPEG metadata extraction across EXIF and COM segments, bit-stream-to-JPEG byte reconstruction, base64-wrapped JPEG with hex content, and surgical magic-byte repair plus XMP metadata walking. ...

Platform HASBL CTF 2026 Difficulty Mixed (Easy → Medium) OS Jeopardy — Pwn (Linux x86-64) Tags ret2win with movaps stack alignment, int16 signed overflow, mmap RWX shellcode injection, register-controlled jmp into pre-built gadget chain, classic ROP with SysV-ABI argument-register setup, pwntools payload construction, checksec mitigation analysis HASBL CTF 2026 is a multi-category jeopardy event with Reverse Engineering, Pwn, Web, and Forensics tracks. This writeup is dedicated to the Pwn track — the five pwn challenges (baby-bufferoverflow, candy-store, baby-shellcoder, jumper, padawan-pwn) were all solved, and each one teaches a different beginner-to-intermediate binary-exploitation primitive: ret2win with the movaps 16-byte stack-alignment trap, a signed-vs-unsigned integer-width bug exploitable via menu interaction, direct shellcode execution on an mmap’d RWX page, a 7-byte shellcode budget that has to set rdx for a hard-coded jmp rdx into the binary’s own gadget chain, and a full ROP chain that loads three argument registers before calling a flag-printing function. ...

Platform HASBL CTF 2026 Difficulty Mixed (Easy → Medium) OS Jeopardy — Reverse Engineering Tags Go binary triage, static-only flag recovery, PE anti-debug bypass (PEB.BeingDebugged, x64dbg process scan, NtCreateThreadEx), custom binary protocol parsing, game-logic reverse engineering HASBL CTF 2026 is a multi-category jeopardy event covering Reverse Engineering, Pwn, Web, and Forensics. This writeup is dedicated to the Reverse Engineering track — the four rev challenges (baby-go, DebugMe, Pr0t0c0l1337, PamukTheCat) were all solved, and each one teaches a different reverse-engineering skill: static-only recognition on a Go binary with debug symbols, anti-debug bypass on a Windows PE, custom binary-protocol parsing on a Linux PIE, and game-logic reverse engineering on a JRPG-shaped crackme. ...

Platform THEM?! CTF 2026 Difficulty Mixed (Easy → Hard) OS Jeopardy (Reverse, Crypto) Tags CHIP-8 emulation, x86-64 PE reverse engineering, Unicorn dynamic emulation, FNV-1a hash recovery, custom bytecode VMs, control-flow flattening, DES weak-key parity, XOR-chain cryptanalysis, modular arithmetic over 10^155 THEM?! CTF 2026 is a large jeopardy event with 85 total challenges across the usual categories. This writeup covers the seven challenges I personally solved, all from the reverse-engineering and cryptography tracks — every one demanded a real RE or cryptanalytic technique end-to-end. The reverse picks range from a CHIP-8 ROM that paints its flag onto a 64×32 screen across ~2⁴⁰ encoder steps per round, to a Windows binary whose VM mutates its own register state during dispatch. The crypto picks are the same shape — three challenges that look obscure on the surface and reduce to a clean number-theory or XOR-algebra invariant once you read carefully. ...

Platform BYUCTF 2026 Difficulty Mixed (Easy → Hard) OS Jeopardy (Crypto, Forensics, Reverse, Web) Tags Coppersmith small-roots, multi-prime RSA, Euler totient tower reduction, YARA constraint solving, NTP/ICMP/HTTP pcap forensics, Go reverse engineering, Python prototype pollution, CSP bypass BYUCTF 2026 is Brigham Young University’s annual capture-the-flag, hosted on the Cyber Jousting infrastructure (chals.cyberjousting.com). The 2026 edition runs fifteen challenges across four classic jeopardy categories — Crypto, Forensics, Reverse, and Web — with a heavy Portal-flavoured forensics arc starring GLaDOS, Wheatley, and the cake-is-a-lie ICMP/NTP/HTTP capture. ...

Platform Hackastra CTF 2026 Difficulty Mixed (Easy → Hard) OS Jeopardy (Web, Crypto, Reverse, Misc, Forensics) Tags JWT, RS256/HS256 confusion, DSA known-nonce, Coppersmith, Feistel inversion, ARM64/x86_64 RE, WASM RE, AWS Cognito, blind SQLi, XSS, LSB stego Hackastra CTF 2026 ran as a jeopardy-style competition on CTFtime (event #3270) with fifteen challenges spanning reverse engineering, web exploitation, cryptography, forensics, and miscellaneous infrastructure bugs. The event’s name plays on the Sanskrit word अस्त्र (astra, meaning “weapon” or “missile”), and the challenges live up to it — every flag in this set rewards a specific, named technique rather than rote tooling. ...

Platform TJCTF 2026 (Thomas Jefferson CTF) Difficulty Easy → Hard OS Mixed: Linux, macOS ARM64, WebAssembly, Network captures Tags JWT crafting, SSRF via URL normalization, Zip Slip, RSA parity oracle, ECDSA timing/Minerva, invalid-curve attacks, Chebyshev matrix exponentiation, ReDoS as side channel, pickle exploitation, PCK parsing, polyglot files, RTP LSB steganography TJCTF 2026 was the kind of multi-day event that rewards breadth — twenty-one challenges spread across web, reverse engineering, cryptography, forensics, and misc, with no single technique cracking more than two boxes. This writeup is the consolidated solve log: one paragraph of prompt + trick + solution per challenge, the actual flag, and the moments worth quoting verbatim. ...

Platform Midnight Sun CTF 2026 Quals Difficulty Trivial OS RISC-V 64-bit Linux Tags strings(1), reading the rules riscal is the kind of challenge that gets harder the more you respect the category label. “Reverse engineering” + “RISC-V” primes you to spin up a cross-disassembler, set up a qemu-user static binary, learn the RV64 calling convention, and start manually annotating decompilation. The intended solve is strings. ...

Platform Midnight Sun CTF 2026 Quals Difficulty Hard OS Linux x86-64 Tags Templated binary RE, radare2 scripting, automated static analysis empols is the kind of challenge that punishes you for trying to solve binaries by hand. The server hands you twenty fresh, randomly-generated x86-64 ELFs in one session and demands the validating input string for each — and you almost certainly cannot reverse-engineer twenty unique binaries fast enough to fit inside the session timeout. The intended path is to recognise that the binaries are generated from a small set of templates, then write a static-analysis engine that detects the template and extracts the answer from disassembly. ...

Platform THCON 2026 (Toulouse Hacking Convention) Difficulty Medium OS Steganography Tags Frequency analysis, binary encoding, PNG carving, LSB steganography PNG3D is the steganography challenge that rewards the simplest possible recon move — frequency analysis — and punishes anyone who tries fancy stego tools first. The challenge file is ~40 MB of UTF-8 text that looks like noise; the trick is to notice that two specific characters make up nearly all of it, in roughly equal numbers, and that’s a binary encoding screaming to be decoded. ...