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hotwater / research archive
CTF Writeup Archive
Exploitation, analysis and challenge solutions. Find the technique behind the flag.
202 writeups
Webhack Solutions
Follow a competition collaboration post and coupon clue, distinguishing the successful lead from misleading QR codes.
The Vandoria Leak — "Operation Nexus Gate"
Chain a Next.js middleware bypass, Server Action SSRF, and a mismatched route check to reach restricted portal data.
The Triangle of the Lost Treasure
Read a deterministic triangle judge's canonical answers and reproduce its hash-derived keystream without playing the rounds.
The Phantom Application
Recover an Android vault's passcode and key derivation from the APK, then decrypt its default ledger offline.
The Forgotten Vault
Search a wordlist-and-PIN password space, derive each AES key with MD5, and validate candidate plaintext padding.
The Cursed Syscall
Translate a seccomp BPF filter into constraints and solve the overlapping argument windows that validate the input.
The Cursed Encryption Oracle
Recover an appended secret one byte at a time by aligning controlled input against repeated AES-ECB blocks.
The Cursed APK
Reverse an APK's oath and environment-dependent token derivation to reproduce the clean-device AES decryption.
The Captain's Last Log
Read an E01 image's chunk structures directly and recover the captain's deleted log from the filesystem evidence.
Tetrix Secrets
Identify an embedded Godot export, inspect two flag-shaped strings, and distinguish the platform-confirmed result from a placeholder.
SocialSync: Vice City Underground
Investigate dynamic profile-attribute updates to find how the application permits an unintended authority change.
Project Black Pearl: The Cursed Engine of Elias Blackthorn
Separate a Windows checker's decoy prefix from its real token chain, then reconstruct the stages leading to the flag.
Poison
Analyze faulty elliptic-curve computations in the supplied output to recover the private value used as the flag.
Pirate's Last Algorithm
Reverse a Windows bytecode VM and its hash check, then reconstruct the authorization key that decrypts the flag.
Operation Zero-Trust — DSI Joint Operations Center
Follow a portal's fallback-route clues to a department JSON endpoint and recover the challenge's protected data.
Map Beneath the Ink
Combine historical-map clues with blue-channel LSB data and ship metadata to reconstruct the three-part vault code.
Ghost Ship Unloaded
Recover a Java loader's embedded keys, decrypt its runtime class, and reconstruct the token-and-seal vault derivation.
Ghost in the Storage
Recover deleted SQLite ciphertext, retrieve a salt from an ADB backup, and combine passphrase fragments for decryption.
Ghost Coordinates
Correlate navigation logs, database waypoints, and image metadata to distinguish the real landfall from planted diversions.
Chronos in the Octet Cage
Analyze a four-dimensional algebra over a composite modulus and exploit its structure to recover the encrypted data.
Captain's Last Assembly: Sector 7 Protocol
Read a Unity assembly's static arrays and reproduce its repeating-key XOR to decrypt the flag without running the game.
Captain's Keygen: The Cursed Treasure Lock
Reduce a four-byte key search with meet-in-the-middle sums, then verify the recovered key against independent checksums.
ARGON: The Silent Vault
Recover an ECDSA nonce-leakage model from diagnostic data and use the recorded parameters to reconstruct the secret key.
Ananya's Shadow
Follow mock social profiles, image metadata, and a deleted configuration diff to open the hidden cache archive.
Vesper — Missed-Handover Recovery
Reverse an RV32IM recovery fixture and reconstruct sensor, power, and RF state to recover the sealed handover records.
The Ledger Access Gate
Trace a small ledger API's access checks to identify the request path that exposes the protected record.
The Export That Never Existed
Reproduce an export from the captured dispatch data and hash the exact bytes produced by the supplied exporter.
Thaw Ladder
Use the supplied FROSTLANG bench kit to understand thaw plans and investigate the live controller's hidden behavior.
SILT Field Rack / Revision D
Decode SPI and NOR evidence, emulate the controller ROM, and reconstruct the restore key for a ChaCha20-Poly1305 capsule.
Rime
Recover a remote stack canary, locate the flag path, and dump the ELF to complete a blind ROP exploit.
Recovering the Sealed Manifest
Recover unreachable Git history and deleted environment data to reconstruct the key for a sealed manifest.
Q.E.D. — Prove the Impossible
Analyze a Rust proof checker for a way to export a proof of falsehood despite its intended logical restrictions.
Poisoned Update
Navigate a controller's staged firmware trial, boot diagnostics, and confirmation logic to reach the protected state.
Neve
Combine a stack overflow, stack/libc disclosures, and a write primitive to plant a path before opening the flag file.
Missing Receipt
Correlate five field-relay artifacts to reconstruct the interrupted export and recover the missing receipt evidence.
Ligatures & Liabilities
Inspect the static site's client-side logic and embedded assets to uncover the hidden data without a backend.
Halo Telemetry Align
Use the telemetry endpoint's one-bit responses to reconstruct the alignment information needed by the challenge.
Glacier
Use crash and output behavior to recover a remote stack canary, locate the binary base, and reach its hidden win function.
Frostline Hall C — Thermal Camera Patrol
Compare two lossless thermal patrol recordings and reconstruct the evidence carried across their frames.
Frost Paw
Model the register machine and its hidden ratchet job to reason about how each submission changes the next state.
Floe
Use a length-prefixed overflow and canary oracle to build a blind ROP exploit, separating decoy flags from the real result.
Embedded Bytecode VM
Locate the runtime-initialized data and reverse the embedded bytecode checker to reconstruct its accepted input.
Drumlin — Frostline Cold Archive (Build 2.4)
Trace the cold archive's request flow and access boundaries through a sequence of observed API interactions.
Drif
Recover a remote stack canary, dump the binary with SROP, and build the final file-reading ROP chain.
Deadbit Thermostat
Distinguish committed NAND state from a corrupt later page, then recover the volatile evidence needed to open the archive.
CryoVault Thaw Interlock (Firmware 4.3)
Analyze the thaw controller's arithmetic limits and maintenance override rather than relying on ordinary temperature requests.
CryoVault Dial Verification
Read the chart's verification marks, order the selected hexadecimal characters, and reconstruct the dial code.
CryoVault 2.0
Work through a ten-stage archive chain in which each recovered answer unlocks the next sealed record.
Conduit Preview — SSTI Filter Bypass
Bypass a Flask label-preview filter to reach server-side template evaluation and recover the challenge flag.
Cold Registry — frost-n04 Vault Release Code
Recover tombstoned registry values from freed copy-on-write pages and reconstruct the purged release code.
Cold Dock
Trace the boundary between Frostline Edge and vaultd to understand how sealed manifests control vault access.
Chronoglyph
Recover evidence from a disk image by tracing filesystem artifacts and reconstructing the hidden data chain.
Borrowed Address — Recovering the Closing Batch
Reconstruct a field-log batch from recovered address and memory evidence, checking the exact exported bytes.
Blizzard
Exploit a length-prefixed stack overflow using a fork-stable canary oracle and a syscall-only ROP chain.
Algebraic Mirage
Recover evolving frame keys from public braid states and shuffled anchors, then decrypt the seven-frame exchange.
Weighty Secrets
Analyze a low-density Merkle–Hellman knapsack and use its superincreasing structure to recover the hidden message.
Two Keepers
XOR two visual secret-sharing images to reveal information that neither share exposes on its own.
Truncated Oracle
Recover hidden LCG state from truncated high-bit observations, then reconstruct the low-byte encryption stream.
Total Recall
Use a leaked stack address and two controlled reads to construct an exploit against a small static binary.
TCTF Misc: Command Fuzzer
Investigate a restricted shell-like service's command vocabulary and use the accepted behavior to recover its hidden data.
TCTF Crypto
Analyze a custom AES variant and checksum cryptogram to recover the key material needed for the protected message.
TCP Schrödinger
Reassemble a TCP stream across sequence-number wraparound while distinguishing injected duplicate segments.
Sparrow Freight Dispatch — Stack Overflow to ret2libc
Exploit a stack overflow in the dispatch service and use the provided runtime to construct a ret2libc chain.
Solana Swap Emulator: SwapAToB Account Puzzle
Investigate a self-contained Solana swap emulator and construct the account arrangement its program expects.
Smooth DH
Exploit a smooth group order to solve a Diffie–Hellman discrete logarithm and reconstruct the shared secret.
Small Private
Apply Wiener's continued-fraction attack to an RSA key whose private exponent is deliberately too small.
Slow Motion
Recover a hidden bitstream from a GIF's red-channel least-significant bits across its animation frames.
Shattered Oracle
Chain partial-nonce ECDSA recovery with the later oracle stages to solve Lunar CTF's Shattered Oracle challenge.
Route 666
Reconstruct a routing incident's BGP changes and follow the exfiltration evidence across the affected sessions.
Related Messages
Use the known relationship between two low-exponent RSA plaintexts to recover the message through polynomial arithmetic.
Pset1
Use the supplied exploit notes to understand an introductory stack overflow and its flag-recovery path.
Phantom Eclipse
Reconstruct a sectioned evidence container using image clues and related artifacts from the supplied bundle.
PerpGuard — Solana Compute-Unit Exhaustion via a Player CPI Program
Use a crafted Solana cross-program invocation to exhaust the compute budget of the target transaction.
Partial Exposure
Use leaked high bits of an RSA prime to formulate the small unknown part for a Coppersmith-style recovery.
Paleter
Inspect a PNG's palette indices and reproduce a palette transformation that reveals the concealed image.
Nostalgia
Recover a weak time seed, reproduce its LCG-derived AES key, and decrypt the captured ciphertext.
Neve
Use statistical inference against a noisy one-bit sounding interface to reconstruct the hidden symbols.
Monodromy
Analyze MONOVM3 matrices and a stripped executable to recover the missing rotation index.
Mirror
Exploit a PIE binary's shared record structure and session behavior to reach the protected state.
Mirage
Use a remote format-string sink and short service interactions to construct the Mirage exploit.
min-beste-venn (Chatflare)
Reconstruct a chat conversation from asset requests recorded in a packet capture of a Cloudflare-fronted app.
Matrix Over Mind
Use a plaintext matrix's known trace and determinant to recover information from matrix-based RSA encryption.
Manifest — Format String Into Clearance
Investigate the manifest feedback terminal's format-string behavior and construct the corresponding binary exploit.
LUN4R-MU Timing Leak
Use timing differences in a small hardware VM's debugger to infer information hidden by its instruction interface.
LMS Firmware Signer: Leaf Zero for Free
Investigate a hash-based firmware signer whose handling of leaf zero undermines its one-time-signature guarantees.
Linear Guess
Recover an LCG's unknown multiplier and increment from consecutive outputs, then reconstruct its XOR keystream.
Ledger — Tcache Poisoning Into free@GOT
Build a heap exploit against the supplied glibc runtime, using tcache poisoning to overwrite the free GOT entry.
KumoSec ChainVault
Analyze an EVM audit registry and vault contract to reconstruct the access path exposed by their interaction.
Kintsugi Vault — Shard Chain, One Byte Chain Piece at a Time
Analyze a stripped shard runtime and its companion agents to reconstruct the vault's chained byte-level checks.
Kairo — Adaptive Instruction Classifier
Exploit an adaptive instruction classifier's trust decision to bypass checks on a program's later behavior.
H7 Passport — Legacy Attestation Path for Enterprise Tier
Analyze WebAuthn attestation validation across three formats to find the inconsistency in the relying party's checks.
Ground
Use a hidden gopher-capable feed override to make an internal report request and recover the result from a rendered PDF.
GitDumper
Recover a source tree from an exposed Git directory by walking loose objects from HEAD without a directory listing.
Ghost in the Wire
Decode a Base85 message in network incident artifacts to recover the flag hidden in plain sight.
GateCache — Heap Reuse Into Another Thread's Session
Exploit heap reuse in a multithreaded C++ service to cross the boundary between separate session objects.
FoundryProof Tiny-HDL Equivalent-but-Sabotaged
Inspect a hardware-equivalence sign-off workflow to find how a sabotaged netlist passes its verification process.
Cut Me
Restore a PNG's truncated height field so that the image data hidden below its advertised dimensions becomes visible.
Cuspidal Drift
Analyze a singular curve whose group structure reduces the custom cryptosystem to a simpler arithmetic problem.
Common Modulus
Combine ciphertexts sharing one RSA modulus using Bézout coefficients for coprime public exponents.
CKKS Approximate-Decryption Key Recovery
Analyze approximate-decryption leakage in a CKKS-style service to recover the encryption key.
BYOC
Construct executable input for a service that maps attacker-supplied bytes into an executable memory region.
Broadcast Linear
Exploit repeated low-exponent RSA messages with known linear padding across three different moduli.
Boneh-Durfee
Recover an RSA private exponent beyond Wiener's bound using the small-root structure behind the Boneh–Durfee attack.
Bit Flip CRT
Use a one-bit RSA-CRT signing fault and a correct signature to factor the modulus with a greatest-common-divisor calculation.
BGP From Hell
Reconstruct exfiltrated data from BGP COMMUNITY attributes distributed across eight UPDATE messages.
auth-gw Biased-Nonce ECDSA
Exploit biased ECDSA nonces in captured secp256k1 session attestations using the parameters recorded in the handout.
Afterglow — DOS Panel ROM Bitplane Reconstruction
Reconstruct hidden panel output from a DOS ROM by analyzing its display data and bitplane organization.
Zygote Conspiracy
Reconstruct the two APKs' shared decryption process by combining their assets and tracing the native memfd exchange.
Turning Chart — Reverse Engineering
Locate the control flow in a stripped static ELF and reverse its validation without function symbols.
Toxic Waste
Exploit the structure of a trusted setup and its published powers to recover the hidden scalar and challenge plaintext.
The Shape of Silence
Recover an exact rational response function from versioned observations and anchors, then evaluate its 24 target inputs.
The Last Committed Message
Reconstruct a committed note and attachment record from four encoded evidence strings at the requested export boundary.
The Image That Forgot
Correlate container artifacts with an incident timestamp to identify the token belonging to the correct running instance.
Sparse-change
Use the structure of a sparse mathematical change to recover hidden information from the supplied generator and output.
signed, but which original?
Trace a derivative's manifest ancestry back to the original capture and recover the six evidence fields the case requires.
PHANTOM-15: The Sensor That Transmitted Nothing
Correlate surviving industrial telemetry to recover a missing report from a device declared permanently offline.
Phantom Mesh
Analyze a suspicious smart-lighting diagnostic report and its supporting artifacts to reconstruct hidden mesh evidence.
Ouroboros — Reverse Engineering
Reverse the transformations in a 32-byte input checker and reconstruct an input that satisfies its arithmetic conditions.
One pound fish
Use reverse image search and a nearby landmark reference to identify the market recorded in the supplied solution.
last packet — Forensics
Inspect HTTP traffic in a packet capture and reconstruct the final message from the recorded requests and responses.
Insanity Check 3 — CRYOVAULT 2026
Inspect the competition's flag-format rule for concealed content that is not visible in its ordinary presentation.
Half-Truths
Recover hidden polynomial information from shuffled finite-field shares and use it to open the AES-GCM ciphertext.
Ghost Spooler — Forensics
Correlate Windows spool metadata, print data, and a scanned page to reconstruct the evidence behind a print job.
Frost-ledger
Recover stale values from an older registry format whose cell descriptors retain evidence after deletion.
Zygote-Conspiracy Bundle
Reverse two cooperating Android apps whose native libraries exchange memory-backed halves of an encrypted payload.
Write-hole
Reconstruct RAID5 layout and interrupted-write evidence, then recover the material needed to open the sealed report.
Turning_chart
Inspect a tiny static ELF's raw-syscall checker and reconstruct its accepted input from the validation logic.
The-press
Reverse a custom LZMA-style range encoder and recover the 32-byte input matching its fixed compressed output.
The Deletion Echo
Compare a regression model's deletion evidence with its retraining claim to recover information that should have disappeared.
The Aggregate Remembers
Recover a hidden client contribution from weighted updates to a federated linear-regression model.
slab store
Analyze Slab's remote protocol and memory behavior to construct the interaction that recovers the protected result.
SilverGate — silvergate.apk + base.odex
Reverse a handcrafted ODEX-like container and its AArch64 code rather than relying on standard ART parsing.
Recurrence
Reverse a stripped ELF's recurrence-based validation and reconstruct the input accepted by the checker.
Prismwake
Recover hidden values from thousands of noisy multiplier observations by exploiting their mathematical structure.
Parallax
Recover fourteen hidden atoms from modular subset-sum observations and reconstruct the binary selection masks.
Palimpsest — Restoration Press 04
Reconstruct surviving archive jobs from the binary's catalogue and job cards to recover the historical data.
loom — Reversible Cellular Automaton Crackme
Reverse a second-order cellular automaton to recover the 32-byte input expected after its long evolution.
Leger
Reverse a stripped ELF's arithmetic predicate to recover the exact 16-byte input that satisfies its ledger check.
leaky-eval — HTB Crypto Challenge
Analyze a polynomial-ring evaluation service and its public output to recover the information hidden by the challenge.
Journal-necromancy
Recover deleted evidence from a small NTFS image by examining surviving filesystem journal records.
Implicit Twins — RSA Lattice Attack
Relate two RSA moduli to recover the private information needed to decrypt a ciphertext under the first key.
Hidden Weights -
Recover ten secret weights from modular totals by exploiting the structure of the published linear constraints.
GHOST-13 offline investigation
Combine journal recovery, network reconstruction, nonce reuse, and audio decoding to recover an authenticated OTA payload.
Free-lunch
Exploit the algebraic structure of a finite-field permutation instead of treating its twenty rounds as a black box.
Field Console
Analyze a handset app's dispatch protocol and maintenance path to reconstruct the privileged interaction.
End Mark
Reassemble 24 fixed-size payloads in slot order and verify the resulting 576-byte message by its SHA-256 hash.
Cryovault Attestation
Trace writable registry state and its attestation workflow to understand the path to the protected artifact.
coldpack — rimefold (IFSCR)
Investigate a fresh-process remote service and reconstruct the interaction needed to solve its low-level state checks.
Cassandra Fintech — cassandra-edge/2.3.1 (IFSCR CTF)
Place restricted headers in HTTP/2 CONTINUATION frames to bypass checks applied only to the initial HEADERS frame.
Canonical-sin
Exploit inconsistent interpretation of signed CBOR capabilities across a Node broker and Python vault service.
The Third Key Phase
Decrypt successive QUIC key phases, reassemble the accepted upload, and derive the flag from its exact file bytes.
The Meridian
Trace a client-rendered application's JavaScript and API behavior to uncover its hidden access path.
The API That Knows Too Much
Exploit missing employee-record authorization and use a leaked debug reference to reach the protected information.
The Alphabet That Wasn't There
Reconstruct the hidden alphabet and verify the recovered evidence using the supplied AES-GCM authentication check.
one-more — Blind Schnorr "one-more" forgery via ROS
Investigate a blind Schnorr signing service and its connection-specific parameters to recover the challenge result.
Mirror Garden
Reverse an app's whisper validator and reconstruct the input that passes its hidden checks.
Lossless Not Harmless
Inspect PNG palette and chunk data to recover information hidden inside an apparently noisy indexed-color image.
LeetVault: The Hidden Test Case
Investigate a legacy problem-search endpoint to recover a hidden test case from the application's exposed behavior.
Keystone — Attestation Portal (boot2root)
Chain template injection, forged TPM attestation, a leaked SSH key, and a symlink race to reach both protected flags.
Ghosts in the Bulb — Local Version
Extract covert data from two devices in an unencrypted MQTT capture and reconstruct their hidden message.
Ghosts in the Bulb
Analyze a smart-home MQTT capture for device-specific covert channels and combine the recovered data.
Fluxgate G3 — Factory Service Mode Bypass
Analyze a line-oriented controller protocol to reach the factory maintenance path intended for on-site technicians.
FlaGuard
Trace the Flaguard solution and its recorded submission result, explaining the checks that lead to the accepted flag.
Faraday
Reverse an Android diagnostic app's native validation to recover the response expected by a smart-bulb challenge.
ECHOCHAMBER — Boot2Root
Work around a root-run warden's decoys and recovery logic to reach the real user and root flag files.
ECHO-9
Correlate watchdog recovery with repeated AES-CTR nonces to reconstruct an earlier protected response.
Draftpad
Trace document pins and shifted indexes to explain why the public export exposes a supposedly private block.
Sensor Logs
Extract a PNG and text fragment from a sensor-log container; the proposed final flag remains checker-unconfirmed.
Redacted Minutes
Recover a DOCX's deleted revisions, decode its hidden archive, and read the flag from trailing whitespace.
Two Faces
Combine PDF metadata, an appended encrypted ZIP, and an orphan object to recover a pad-protected message.
Port 0xBEEF (Hyper-Nested)
Reconstruct a nested networking incident's evidence chain, including its encoded flag-format conventions.
Orisond
Analyze Orisond's binary command protocol and address disclosures to reconstruct the exploit's memory interaction.
Nested Steam Package
Inspect a nested archive's manifest before following deeper decoys; the useful result is already in its playlist file.
Neon Relic (07_neon_relic.mid)
Extract a ZIP appended to a MIDI file, then read a hidden bitmap from the recovered PNG's top pixel rows.
Double Exposure
Follow JPEG metadata and embedded content to reconstruct the evidence hidden by the double-exposure challenge.
Biased Nonce
Recover an ECDSA key from nonces with eight missing high bits by formulating the resulting lattice problem.
Shadow Consent
Correlate incident artifacts to reconstruct the consent and access activity behind a data-security investigation.
Welcome
Inspect a packet capture and reconstruct the flag carried by its recorded communication.
TOMORROW-MART — SunshineCTF 2026
Trace a storefront discount and its bank integration to acquire the protected vault deed despite a limited starting balance.
Chrome Horizon — Manual Solve
Use a JWT key-identifier path traversal to sign an editor token with a known public stylesheet.
St. Cascade General — Mid-Run Ransomware
Analyze a LiME memory capture from a ransomware incident to recover the material needed to decrypt a locked document.
Hothouse
Reverse a linear cellular automaton, recover its packed state, and reconstruct the input expected by the simulator.
Countersign attestation core v2
Reverse the countersign attestation protocol and build a protocol-only solver for its 24-byte RUN payload.
Sparrow Freight API — Leaked Production Token
Investigate repository artifacts beyond the clean commit history to recover the missing carrier token.
Onyx Locker 2.4.0 (mobile)
Reverse an Android password manager and its backend interaction to recover information hidden by the app's UI.
MURMUR v1.2 Mesh Control Protocol
Analyze the MURMUR mesh control-channel profile and its captured traffic to reconstruct the protected communication.
FlyWithHer.io
Use a vulnerable preview fetcher to inspect internal documentation, derive a dated endpoint, and decode its returned gift.
DeputyCorp Cloud Integration — AWS IAM Privilege Escalation
Trace an AWS-style cloud integration's IAM permissions to identify the privilege-escalation path available to its starting identity.
Deleting a Thing
Recover a deleted message by investigating the gap in a SQLite message table and the surrounding evidence.
CherryPic — Cybercom
Trace an uploaded DjVu file through an outdated ExifTool parser to explain the challenge's command-execution path.
"sudo zip, sudo shred, zero proof"
Inspect a filesystem image with read-only ext tools to reconstruct evidence left by sudo zip and shred activity.
Lunar Forensic Challenge 4
Follow a PNG's metadata through a protected appended ZIP, then decode the extracted image's hidden bitstream.
Roulette Online
Investigate roulette wager arithmetic to reach the required balance without relying on a normal sequence of winning spins.
ET — Tu Brute
Examine a Caesar-cipher challenge note and its recorded answer, with the missing derivation made explicit.
Blackout Gateway
Trace a simulated gateway's SSRF and JWT trust boundaries to reconstruct the route into its admin console.
Web Hacker 2
Follow an introductory IDOR trail and change the boarding-pass API's object reference to retrieve the admin record.
Hiding in Your Wi-Fi
Analyze a local network's traffic and available interception tools to recover the hidden wireless-network evidence.
VVDrug Cartel — Web
Challenge note only: the preserved prompt does not yet document a solution, exploit, or verified result.
The Secure Trust Bank — RAG Data Leakage
Examine how a chatbot's retrieval layer exposes restricted documents and use the leaked material to solve the challenge.
SecureTrust Mobile — Forgotten
Inspect a mobile QA build and its supporting data to reconstruct the forgotten access path.
SecureTrust Cluster Registry
Escalate a restricted Kubernetes service account through the registry portal to reach the cluster's protected secret.
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