> For the complete documentation index, see [llms.txt](https://ctf.zeyu2001.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ctf.zeyu2001.com/2021.md).

# 2021

- [hxp CTF 2021](https://ctf.zeyu2001.com/2021/hxp-ctf-2021.md)
- [HTX Investigator's Challenge 2021](https://ctf.zeyu2001.com/2021/htx-investigators-challenge-2021.md)
- [Metasploit Community CTF](https://ctf.zeyu2001.com/2021/metasploit-community-ctf.md): Hosted by Rapid7 from 4 Dec to 7 Dec 2021
- [MetaCTF CyberGames](https://ctf.zeyu2001.com/2021/metactf-cybergames.md): MetaCTF's 7th annual virtual jeopardy-style CTF, held from 4 Dec to 6 Dec 2021
- [Look, if you had one shot](https://ctf.zeyu2001.com/2021/metactf-cybergames/look-if-you-had-one-shot.md)
- [Custom Blog](https://ctf.zeyu2001.com/2021/metactf-cybergames/custom-blog.md)
- [Yummy Vegetables](https://ctf.zeyu2001.com/2021/metactf-cybergames/yummy-vegetables.md)
- [Ransomware Patch](https://ctf.zeyu2001.com/2021/metactf-cybergames/ransomware-patch.md)
- [I Hate Python](https://ctf.zeyu2001.com/2021/metactf-cybergames/i-hate-python.md)
- [Interception](https://ctf.zeyu2001.com/2021/metactf-cybergames/interception.md)
- [CyberSecurityRumble CTF](https://ctf.zeyu2001.com/2021/cybersecurityrumble-ctf.md)
- [Lukas App](https://ctf.zeyu2001.com/2021/cybersecurityrumble-ctf/lukas-app.md)
- [Finance Calculat0r 2021](https://ctf.zeyu2001.com/2021/cybersecurityrumble-ctf/finance-calculat0r-2021.md)
- [Personal Encryptor with Nonbreakable Inforation-theoretic Security](https://ctf.zeyu2001.com/2021/cybersecurityrumble-ctf/personal-encryptor-with-nonbreakable-inforation-theoretic-security.md)
- [Enterprice File Sharing](https://ctf.zeyu2001.com/2021/cybersecurityrumble-ctf/enterprice-file-sharing.md)
- [Payback](https://ctf.zeyu2001.com/2021/cybersecurityrumble-ctf/payback.md)
- [Stonks Street Journal](https://ctf.zeyu2001.com/2021/cybersecurityrumble-ctf/stonks-street-journal.md)
- [The InfoSecurity Challenge (TISC) 2021](https://ctf.zeyu2001.com/2021/the-infosecurity-challenge-tisc-2021.md): TISC is an online challenge organised by CSIT since 2020. It provides opportunities for interested Singaporeans to put their cybersecurity and programming skills to the test by solving challenging puz
- [Level 4 - The Magician's Den](https://ctf.zeyu2001.com/2021/the-infosecurity-challenge-tisc-2021/level-4-the-magicians-den.md)
- [Level 3 - Needle in a Greystack](https://ctf.zeyu2001.com/2021/the-infosecurity-challenge-tisc-2021/level-3-needle-in-a-greystack.md)
- [Level 2 - Dee Na Saw as a need](https://ctf.zeyu2001.com/2021/the-infosecurity-challenge-tisc-2021/level-2-dee-na-saw-as-a-need.md)
- [Level 1 - Scratching the Surface](https://ctf.zeyu2001.com/2021/the-infosecurity-challenge-tisc-2021/level-1-scratching-the-surface.md)
- [SPbCTF's Student CTF Quals](https://ctf.zeyu2001.com/2021/spbctfs-student-ctf-quals.md): Student CTF is a novice-level Capture The Flag organized by SPbCTF and supported by St. Petersburg Committee for Science and Higher Education.
- [31 Line PHP](https://ctf.zeyu2001.com/2021/spbctfs-student-ctf-quals/31-line-php.md)
- [BLT](https://ctf.zeyu2001.com/2021/spbctfs-student-ctf-quals/blt.md)
- [CatStep](https://ctf.zeyu2001.com/2021/spbctfs-student-ctf-quals/catstep.md)
- [Asian Cyber Security Challenge (ACSC) 2021](https://ctf.zeyu2001.com/2021/asian-cyber-security-challenge-acsc-2021.md): The ACSC is the regional final of the International Cybersecurity Challenge (ICC) — a global CTF competition, supported by the European Union Agency for Cybersecurity (ENISA).
- [Cowsay As A Service](https://ctf.zeyu2001.com/2021/asian-cyber-security-challenge-acsc-2021/cowsay-as-a-service.md): Prototype pollution leads to RCE
- [Favorite Emojis](https://ctf.zeyu2001.com/2021/asian-cyber-security-challenge-acsc-2021/favorite-emojis.md): Prerender dynamic rendering leads to SSRF
- [Baby Developer](https://ctf.zeyu2001.com/2021/asian-cyber-security-challenge-acsc-2021/baby-developer.md): Directory traversal in insecure Vitepress development server leads to information disclosure through SSRF
- [API](https://ctf.zeyu2001.com/2021/asian-cyber-security-challenge-acsc-2021/api.md): Logic error in user authentication
- [RSA Stream](https://ctf.zeyu2001.com/2021/asian-cyber-security-challenge-acsc-2021/rsa-stream.md): RSA common modulus attack
- [Filtered](https://ctf.zeyu2001.com/2021/asian-cyber-security-challenge-acsc-2021/filtered.md): Buffer overflow with a flawed length check
- [NYONG Coin](https://ctf.zeyu2001.com/2021/asian-cyber-security-challenge-acsc-2021/nyong-coin.md): EnCase forensics
- [CSAW CTF Qualification Round 2021](https://ctf.zeyu2001.com/2021/csaw-ctf-qualification-round-2021.md): Hosted by members of NYU Tandon School of Engineering’s OSIRIS Lab
- [Save the Tristate](https://ctf.zeyu2001.com/2021/csaw-ctf-qualification-round-2021/save-the-tristate.md): Quantum Key Distribution (QKD)
- [securinotes](https://ctf.zeyu2001.com/2021/csaw-ctf-qualification-round-2021/securinotes.md): Meteor NoSQL Injection
- [no pass needed](https://ctf.zeyu2001.com/2021/csaw-ctf-qualification-round-2021/no-pass-needed.md): Filtered SQL injection
- [Gatekeeping](https://ctf.zeyu2001.com/2021/csaw-ctf-qualification-round-2021/gatekeeping.md): Bypassing Nginx directive through manipulating Gunicorn WSGI variables
- [Ninja](https://ctf.zeyu2001.com/2021/csaw-ctf-qualification-round-2021/ninja.md): Flask Server-Side Template Injection (SSTI)
- [YauzaCTF 2021](https://ctf.zeyu2001.com/2021/yauzactf-2021.md): Hosted by SFT0 from BMSTU
- [Yauzacraft Pt. 2](https://ctf.zeyu2001.com/2021/yauzactf-2021/yauzacraft-pt.-2.md): Unrestricted file upload leads to PHP webshell
- [Yauzabomber](https://ctf.zeyu2001.com/2021/yauzactf-2021/yauzabomber.md): Server-Side Template Injection (SSTI) in SMS template
- [RISC 8bit CPU](https://ctf.zeyu2001.com/2021/yauzactf-2021/risc-8bit-cpu.md): Writing an emulator / disassembler
- [ARC6969 Pt. 1](https://ctf.zeyu2001.com/2021/yauzactf-2021/arc6969-pt.-1.md): Writing an emulator / disassembler
- [ARC6969 Pt. 2](https://ctf.zeyu2001.com/2021/yauzactf-2021/arc6969-pt.-2.md): Writing an emulator / disassembler
- [Back in 1986 - User](https://ctf.zeyu2001.com/2021/yauzactf-2021/back-in-1986-user.md): Morris Worm - fingerd Stack Buffer Overflow and Cron Job misconfiguration
- [Lorem-Ipsum](https://ctf.zeyu2001.com/2021/yauzactf-2021/lorem-ipsum.md): Zero-Width Space (ZWSP) Stegonography
- [InCTF 2021](https://ctf.zeyu2001.com/2021/inctf-2021.md): The fifth international edition of InCTF, hosted by team bi0s
- [Notepad 1 - Snakehole's Secret](https://ctf.zeyu2001.com/2021/inctf-2021/notepad-1-snakeholes-secret.md): Stored XSS and Response Header Injection Leads to CSRF
- [RaaS](https://ctf.zeyu2001.com/2021/inctf-2021/raas.md): SSRF using Gopher protocol leads to tampering of Redis key-value store
- [MD Notes](https://ctf.zeyu2001.com/2021/inctf-2021/md-notes.md): postMessage information disclosure leads to stored XSS
- [Shell Boi](https://ctf.zeyu2001.com/2021/inctf-2021/shell-boi.md): Unencrypted remote shell leads to TCP session hijacking and RCE through man-in-the-middle (MITM) attack
- [Listen](https://ctf.zeyu2001.com/2021/inctf-2021/listen.md): Basic packet sniffing and analysis
- [Ermittlung](https://ctf.zeyu2001.com/2021/inctf-2021/ermittlung.md): Basic memory forensics
- [Alpha Pie](https://ctf.zeyu2001.com/2021/inctf-2021/alpha-pie.md): Breadth-first Search algorithm for a fun programming task
- [UIUCTF 2021](https://ctf.zeyu2001.com/2021/uiuctf-2021.md): UIUCTF is an annual Capture the Flag competition run by undergraduate students at the University of Illinois at Urbana-Champaign (UIUC).
- [pwnies\_please](https://ctf.zeyu2001.com/2021/uiuctf-2021/pwnies_please.md): Adversarial attack on an image classifier using the Fast Gradient Sign Method (FGSM)
- [yana](https://ctf.zeyu2001.com/2021/uiuctf-2021/yana.md): GitHub Pages subdomain takeover and cache probing XS-Leak
- [ponydb](https://ctf.zeyu2001.com/2021/uiuctf-2021/ponydb.md): SQL injection and truncation attack
- [SUPER](https://ctf.zeyu2001.com/2021/uiuctf-2021/super.md): Decoding an XOR-encoded file gives us an MS-DOS VHD
- [Q-Rious Transmissions](https://ctf.zeyu2001.com/2021/uiuctf-2021/q-rious-transmissions.md): Superdense coding quantum communication protocol
- [capture the :flag:](https://ctf.zeyu2001.com/2021/uiuctf-2021/capture-the-flag.md): LSB steganography
- [back\_to\_basics](https://ctf.zeyu2001.com/2021/uiuctf-2021/back_to_basics.md): Simple beginner challenge about base-n encodings
- [buy\_buy\_buy](https://ctf.zeyu2001.com/2021/uiuctf-2021/buy_buy_buy.md): A Discord marketplace!
- [Google CTF 2021](https://ctf.zeyu2001.com/2021/google-ctf-2021.md): Annual Capture The Flag hosted by the Google Security Team.
- [CPP](https://ctf.zeyu2001.com/2021/google-ctf-2021/cpp.md): We have this program's source code, but it uses a strange DRM solution. Can you crack it?
- [Filestore](https://ctf.zeyu2001.com/2021/google-ctf-2021/filestore.md): We stored our flag on this platform, but forgot to save the id. Can you help us restore it?
- [TyphoonCon CTF 2021](https://ctf.zeyu2001.com/2021/typhooncon-ctf-2021.md): Hosted by SSD Secure Disclosure
- [Clubmouse](https://ctf.zeyu2001.com/2021/typhooncon-ctf-2021/clubmouse.md)
- [Impasse](https://ctf.zeyu2001.com/2021/typhooncon-ctf-2021/impasse.md)
- [DSTA BrainHack CDDC21](https://ctf.zeyu2001.com/2021/dsta-brainhack-cddc21.md)
- [File It Away (Pwn)](https://ctf.zeyu2001.com/2021/dsta-brainhack-cddc21/file-it-away-pwn.md)
- [Linux Rules the World! (Linux)](https://ctf.zeyu2001.com/2021/dsta-brainhack-cddc21/linux-rules-the-world-linux.md)
- [Going Active (Reconnaissance)](https://ctf.zeyu2001.com/2021/dsta-brainhack-cddc21/going-active-reconnaissance.md)
- [Behind the Mask (Windows)](https://ctf.zeyu2001.com/2021/dsta-brainhack-cddc21/behind-the-mask-windows.md)
- [Web Takedown Episode 2 (Web)](https://ctf.zeyu2001.com/2021/dsta-brainhack-cddc21/web-takedown-episode-2-web.md)
- [Break it Down (Crypto)](https://ctf.zeyu2001.com/2021/dsta-brainhack-cddc21/break-it-down-crypto.md)
- [BCACTF 2.0](https://ctf.zeyu2001.com/2021/bcactf-2.0.md): I didn't have much time to play this one, but the challenges that I did try were definitely fun!
- [L10N Poll](https://ctf.zeyu2001.com/2021/bcactf-2.0/l10n-poll.md): jsonwebtoken authentication bypass vulnerability.
- [Challenge Checker](https://ctf.zeyu2001.com/2021/bcactf-2.0/challenge-checker.md): PyYAML deserialisation vulnerability (CVE-2020-14343).
- [Discrete Mathematics](https://ctf.zeyu2001.com/2021/bcactf-2.0/discrete-mathematics.md): Buffer overflow, with a ROP chain.
- [Advanced Math Analysis](https://ctf.zeyu2001.com/2021/bcactf-2.0/advanced-math-analysis.md): Buffer overflow, with a strcmp() check.
- [Math Analysis](https://ctf.zeyu2001.com/2021/bcactf-2.0/math-analysis.md): Classic buffer overflow.
- [American Literature](https://ctf.zeyu2001.com/2021/bcactf-2.0/american-literature.md): Format string vulnerability.
- [More Than Meets the Eye](https://ctf.zeyu2001.com/2021/bcactf-2.0/more-than-meets-the-eye.md): Zero-width space (ZWSP)
- [􃗁􌲔􇺟􊸉􁫞􄺷􄧻􃄏􊸉](https://ctf.zeyu2001.com/2021/bcactf-2.0/undefined.md): Unicode substitution cipher.
- [Zh3ro CTF V2](https://ctf.zeyu2001.com/2021/zh3ro-ctf-v2.md): Web and Crypto challenges from Zh3r0 CTF V2 hosted from 4 June - 6 June 2021!
- [Chaos](https://ctf.zeyu2001.com/2021/zh3ro-ctf-v2/chaos.md): Collisions in the chaotic hash function.
- [Twist and Shout](https://ctf.zeyu2001.com/2021/zh3ro-ctf-v2/twist-and-shout.md): Recovering the internal state of Python's Mersenne Twister PRNG.
- [1n\_jection](https://ctf.zeyu2001.com/2021/zh3ro-ctf-v2/1n_jection.md)
- [alice\_bob\_dave](https://ctf.zeyu2001.com/2021/zh3ro-ctf-v2/alice_bob_dave.md): Common factor in RSA modulus.
- [Baby SSRF](https://ctf.zeyu2001.com/2021/zh3ro-ctf-v2/baby-ssrf.md): SSRF blacklist bypass enabled internal port scan and access to hidden endpoints.
- [bxxs](https://ctf.zeyu2001.com/2021/zh3ro-ctf-v2/bxxs.md): XSS leads to information leakage of hidden endpoint and authentication bypass.
- [Sparta](https://ctf.zeyu2001.com/2021/zh3ro-ctf-v2/sparta.md): node.js deserialization vulnerability leads to RCE.
- [Pwn2Win CTF 2021](https://ctf.zeyu2001.com/2021/pwn2win-ctf-2021.md): As one of the DEFCON pre-qualifiers, this was definitely a challenging CTF. The challenges were high-quality, and felt extremely realistic.
- [C'mon See My Vulns](https://ctf.zeyu2001.com/2021/pwn2win-ctf-2021/cmon-see-my-vulns.md): PHP eval(), LD\_PRELOAD RCE
- [Illusion](https://ctf.zeyu2001.com/2021/pwn2win-ctf-2021/illusion.md): JavaScript Prototype Injection
- [NorzhCTF 2021](https://ctf.zeyu2001.com/2021/norzhctf-2021.md): This was my first time doing a Hack Quest CTF. The challenges were quite fun, especially because they are more realistic than most CTF challenges.
- [Leet Computer](https://ctf.zeyu2001.com/2021/norzhctf-2021/leet-computer.md): Pentesting, Ghidra JDWP RCE, Sudo Misconfiguration, NSE Scripting
- [Secure Auth v0](https://ctf.zeyu2001.com/2021/norzhctf-2021/secure-auth-v0.md): Reverse Engineering
- [Triskel 3: Dead End](https://ctf.zeyu2001.com/2021/norzhctf-2021/triskel-3-dead-end.md): Werkzeug Debugger Console RCE
- [Triskel 2: Going In](https://ctf.zeyu2001.com/2021/norzhctf-2021/triskel-2-going-in.md): SQL Injection
- [Triskel 1: First Contact](https://ctf.zeyu2001.com/2021/norzhctf-2021/triskel-1-first-contact.md): Server-side Request Forgery (SSRF)
- [Discovery](https://ctf.zeyu2001.com/2021/norzhctf-2021/discovery.md)
- [DawgCTF 2021](https://ctf.zeyu2001.com/2021/dawgctf-2021.md): Hosted by the UMBC CyberDawgs.
- [Bofit](https://ctf.zeyu2001.com/2021/dawgctf-2021/bofit.md): Buffer overflow
- [Jellyspotters](https://ctf.zeyu2001.com/2021/dawgctf-2021/jellyspotters.md): Python pickle deserialisation
- [No Step On Snek](https://ctf.zeyu2001.com/2021/dawgctf-2021/no-step-on-snek.md): Python input() vulnerability
- [Back to the Lab 2](https://ctf.zeyu2001.com/2021/dawgctf-2021/back-to-the-lab-2.md): LabVIEW
- [MDL Considered Harmful](https://ctf.zeyu2001.com/2021/dawgctf-2021/mdl-considered-harmful.md): ImageMagick CVE-2016-3717
- [Really Secure Algorithm](https://ctf.zeyu2001.com/2021/dawgctf-2021/really-secure-algorithm.md): Wiener's attack on RSA
- [The Obligatory RSA Challenge](https://ctf.zeyu2001.com/2021/dawgctf-2021/the-obligatory-rsa-challenge.md): RSA with factorable n
- [Trash Chain](https://ctf.zeyu2001.com/2021/dawgctf-2021/trash-chain.md): Reverse engineering a hash function
- [What the Flip?!](https://ctf.zeyu2001.com/2021/dawgctf-2021/what-the-flip.md): AES CBC Byte Flipping Attack
- [Back to the Lab 1](https://ctf.zeyu2001.com/2021/dawgctf-2021/back-to-the-lab-1.md): LabVIEW
- [Back to the Lab 3](https://ctf.zeyu2001.com/2021/dawgctf-2021/back-to-the-lab-3.md): LabVIEW
- [Dr. Hrabowski's Great Adventure](https://ctf.zeyu2001.com/2021/dawgctf-2021/dr.-hrabowskis-great-adventure.md): SQL Injection
- [Just a Comment](https://ctf.zeyu2001.com/2021/dawgctf-2021/just-a-comment.md): Wireshark
- [Baby's First Modulation](https://ctf.zeyu2001.com/2021/dawgctf-2021/babys-first-modulation.md): GNURadio
- [Two Truths and a Fib](https://ctf.zeyu2001.com/2021/dawgctf-2021/two-truths-and-a-fib.md): Programming
- [UMDCTF 2021](https://ctf.zeyu2001.com/2021/umdctf-2021.md): What a fun CTF! Cheers to my team, Social Engineering Xperts for placing 8th overall.
- [Advantageous Adventures](https://ctf.zeyu2001.com/2021/umdctf-2021/advantageous-adventures.md)
- [Roy's Randomness](https://ctf.zeyu2001.com/2021/umdctf-2021/roys-randomness.md)
- [Whose Base Is It Anyway](https://ctf.zeyu2001.com/2021/umdctf-2021/whose-base-is-it-anyway.md)
- [Cards Galore](https://ctf.zeyu2001.com/2021/umdctf-2021/cards-galore.md)
- [Pretty Dumb File](https://ctf.zeyu2001.com/2021/umdctf-2021/pretty-dumb-file.md)
- [Minetest](https://ctf.zeyu2001.com/2021/umdctf-2021/minetest.md)
- [Donnie Docker](https://ctf.zeyu2001.com/2021/umdctf-2021/donnie-docker.md)
- [Subway](https://ctf.zeyu2001.com/2021/umdctf-2021/subway.md)
- [Jump Not Easy](https://ctf.zeyu2001.com/2021/umdctf-2021/jump-not-easy.md)
- [To Be XOR Not To Be](https://ctf.zeyu2001.com/2021/umdctf-2021/to-be-xor-not-to-be.md)
- [Office Secrets](https://ctf.zeyu2001.com/2021/umdctf-2021/office-secrets.md)
- [L33t M4th](https://ctf.zeyu2001.com/2021/umdctf-2021/l33t-m4th.md)
- [Bomb 2 - Mix Up](https://ctf.zeyu2001.com/2021/umdctf-2021/bomb-2-mix-up.md)
- [Jay](https://ctf.zeyu2001.com/2021/umdctf-2021/jay.md)
- [Midnight Sun CTF 2021](https://ctf.zeyu2001.com/2021/midnight-sun-ctf.md)
- [Corporate MFA](https://ctf.zeyu2001.com/2021/midnight-sun-ctf/corporate-mfa.md): PHP object injection (deserialization vulnerability)
- [Gurkburk](https://ctf.zeyu2001.com/2021/midnight-sun-ctf/gurkburk.md): Python pickle deserialization vulnerability
- [Backups](https://ctf.zeyu2001.com/2021/midnight-sun-ctf/backups.md): RSA factordb attack
- [picoCTF 2021](https://ctf.zeyu2001.com/2021/picoctf.md): This CTF was a blast! I enjoyed many of the Web Exploitation challenges in particular. Here are some of the more interesting challenges I solved.
- [It Is My Birthday (100)](https://ctf.zeyu2001.com/2021/picoctf/it-is-my-birthday-100.md): MD5 collisions
- [Super Serial (130)](https://ctf.zeyu2001.com/2021/picoctf/super-serial-130.md): PHP object injection (deserialization vulnerability)
- [Most Cookies (150)](https://ctf.zeyu2001.com/2021/picoctf/most-cookies-150.md): Flask client-side sessions, cookie forgery
- [Startup Company (180)](https://ctf.zeyu2001.com/2021/picoctf/startup-company-180.md): SQLite injection
- [X marks the spot (250)](https://ctf.zeyu2001.com/2021/picoctf/x-marks-the-spot-250.md): Blind XPath injection
- [Web Gauntlet (170 + 300)](https://ctf.zeyu2001.com/2021/picoctf/web-gauntlet-170-+-300.md): Filtered SQLite injection
- [Easy Peasy (40)](https://ctf.zeyu2001.com/2021/picoctf/easy-peasy-40.md): One-time-pad (OTP) key reuse
- [Mini RSA (70)](https://ctf.zeyu2001.com/2021/picoctf/mini-rsa-70.md): RSA with low exponent
- [Dachshund Attacks (80)](https://ctf.zeyu2001.com/2021/picoctf/dachshund-attacks-80.md): Wiener's attack
- [No Padding, No Problem (90)](https://ctf.zeyu2001.com/2021/picoctf/no-padding-no-problem-90.md): RSA chosen-ciphertext attack (CCA)
- [Trivial Flag Transfer Protocol (90)](https://ctf.zeyu2001.com/2021/picoctf/trivial-flag-transfer-protocol-90.md): Wireshark + steganography
- [Wireshark twoo twooo two twoo... (100)](https://ctf.zeyu2001.com/2021/picoctf/wireshark-twoo-twooo-two-twoo...-100.md): DNS exfiltration
- [Disk, Disk, Sleuth! (110 + 130)](https://ctf.zeyu2001.com/2021/picoctf/disk-disk-sleuth-110-+-130.md): Disk image analysis
- [Stonks (20)](https://ctf.zeyu2001.com/2021/picoctf/stonks-20.md): Format string vulnerability
- [DSO-NUS CTF 2021](https://ctf.zeyu2001.com/2021/dso-nus-ctf.md)
- [Insecure (100)](https://ctf.zeyu2001.com/2021/dso-nus-ctf/insecure-100.md): Privilege escalation through SUID files and PATH variable manipulation
- [Easy SQL (200)](https://ctf.zeyu2001.com/2021/dso-nus-ctf/easy-sql-200.md): Filtered MariaDB injection, stacked queries