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Web3, Free Candy, and exploits galore

Author
JonLuca De Caro
Published
2022/02/26
Updated
2022/04/01
Article Outline

On 1/4/22, nearly 4000 Solana NFT projects were drained of their funds due to a reinitialization bug present in the Candy Machine v1 smart contract on Solana. The account, cHfYkrVAwfEoe3Mr2GbvzpNQJboDL6AiBoFZDsf8dxj, converted 1,027 SOL into 155k USDC using Raydium, and then transferred the USDC into their FTX account. The vulnerability was patched while the attack was actively going on, at 6:20am on 1/4/22.

This investigation uncovered similar vulnerabilities in NFT exchanges, yet to be publicized.

Background

Metaplex's Candy Machine, a Solana program which handles the logistics of NFT issuance, just launched last September. You instantiate it with their CLI, feed it your images, and it handles the rest. It will deal with all the technically complex parts of putting the images on chain and creating the smart contracts to mint them to the buyers.

It’s extremely simple to launch an NFT sale with Metaplex; you choose the price you want to set, the timing of the collection drop and any other configs - it handles the rest and mints right to recipients wallets.

This simplicity greatly lowered the barrier to entry - you didn't need to have any Rust knowledge or Solana API experience to use it. When it first came out it led to a huge increase in NFT collections.

Since its inception, over 14,800 candy machines have been created, each corresponding to an NFT collection.

{% include image.html file="cm-program-solscan" alt="Candy Machine program" %}

Impact

The goal of this research was to identify how the attacker exploited the vulnerability, trace the funds and their total dollar denominated value, and then to determine which projects were impacted.

The attacker targeted 4,410 of the 14,800 candy machines that were created at the time. I'm guessing they didn't target every vulnerable program because they had trouble pulling the historical candy machine creation records.

They fired off withdrawal transactions that took advantage of the reinitialization bug over the period of an hour.

The withdrawal transactions lasted between 5:57am and 6:49am EST on January 4th 2022. At 6:20am, the patched contract was deployed, causing every subsequent transaction by the attacker to fail.

Of the 4,410 candy machines targeted, 3,470 were completely drained. The vulnerability didn't give the attacker permanent control of the candy machines - only for the duration of that transaction, which means that the candy machines that were impacted are not currently vulnerable.

Some of the notable projects impacted by this vulnerability are SolSteads, Contrastive, and Degen Ape Society, with a full list below.

Vulnerability

The bug was subtle - the attacker was injecting pre-initialized accounts and the program was not checking if the account had already been initialized, meaning an attacker could populate their own address as the authority of the contract.

The fix itself was fairly straightforward.

{% include image.html file="candy-machine-fix" alt="Fix for the vulnerability" %}

The hack seems fairly unsophisticated - the damage this vulnerability could do was pretty high, as the bug effectively allowed any account to control the Candy Machine. The attacker submitted the transactions slowly, and would probably have been able to capture the entirety of the vulnerable set of candy machines had they submitted the transactions through their own RPC pool without rate limits.

What's also interesting about the fix is that it was actually fixed in code on December 31st for Candy Machine v2, but the CMv1 contract wasn't redeployed until it was actively being exploited.

Fund extraction

The attacker used Serum DEX and RaydiumSwapV2 to convert the SOL to USDC, then sent the USDC to a FTX address. It should be fairly easy to reverse their idea from FTXs end if they've KYC'd properly.

{% include image.html file="candy-machine-withdrawal" alt="Withdrawal transaction" %}

Candy Machine

Candy Machine v1 is now deprecated, and any new candy machines created should be v2s. From their docs:

The second iteration of the well-known Candy Machine, a fully on-chain generative NFT distribution program, provides many improvements over its predecessor. The new version also allows you to create a whole new set of distribution scenarios and offers protection from bot attacks, while providing the same easy-to-use experience.

Research

Querying for historical data on chain in Solana is a time consuming process. I tried doing research in jupyter notebook at first, but the volume of data made it hard to parse and query.

I ended up cloning the historical transactions into a local database, and indexing that for faster queries.

export class MongoClient {
  init = async () => {
    log.info("Connecting...");
    await connect("mongodb://127.0.0.1:27017", {
      keepAlive: true,
      keepAliveInitialDelay: 300000,
      dbName: "candymachine",
      minPoolSize: 50,
      maxPoolSize: 500,
    });
    log.info("Connected to mongo db");
  };

  saveHashes = async (hashes: object[]) => {
    log.debug("Saving batch...");
    try {
      await Txhashes.insertMany(hashes, { ordered: false });
    } catch (e: any) {
      // ignore dup key errors
      if (!e.message.includes("E11000")) {
        log.error(e);
      }
    }
    const count = await Txhashes.count();
    log.debug(`Saved batch - ${count} total documents`);
  };

  getHashes = async (filter: FilterQuery<typeof Txhashes> = {}) => {
    const docs = await Txhashes.find(filter).limit(25000);
    return docs;
  };
}

I first cloned all the transaction hashes into Mongo - I set up a connection pool of various RPCs to accomplish this, as there's no way of getting it from the Solana mainnet-beta RPC in a reasonable amount of time.


 const history = await con.getSignaturesForAddress(
    new PublicKey(publicKey),
    options
  );

 for (const c of chunk(history, 100000)) {
    await mc.saveHashes(c);
    log.info("Completed chunk");
  }

Then, after fetching all the hashes, I would clone the parsed transaction details into Mongo

const run = async () => {
  await mc.init();
  log.info("Fetching hashes");
  let hashesToFetch = await mc.getHashes({ tx: null });
  log.info("Fetched hashes");
  let i = 0;
  while (hashesToFetch.length) {
    let isNearEnd = hashesToFetch.length < 10000;
    const chunkSize = isNearEnd ? 10 : 200;
    if (isNearEnd) {
      shuffle(hashesToFetch);
    }
    const chunkedHistory = chunk(hashesToFetch, chunkSize) as string[][];
    const processChunk = async (hashes: any[]) => {
      let message = `Fetched txs ${i}`;
      let savedTxMessage = `Saved txs ${i}`;
      i++;

      console.time(message);
      const hashMap = {};
      hashes.forEach((hash) => {
        if (hash.signature) {
          hashMap[hash.signature] = hash;
        } else {
          console.error("what");
        }
      });

      try {
        const { c, tx: txs } = await fetchTxsWithFallbackWithConnection(
          hashes.map((p) => p.signature)
        );

        console.timeLog(message, c?._rpcEndpoint);
        console.timeEnd(message);
        let failureCount = 0;
        txs.forEach((tx) => {
          if (!tx) {
            failureCount++;

            return;
          }
          tx.transaction.signatures.forEach((s) => {
            if (hashMap[s]) {
              hashMap[s].tx = tx;
            }
          });
        });
        if (failureCount) {
          console.error(`Invalid txs: ${failureCount}`);
        }
        console.time(savedTxMessage);
        await Txhashes.bulkSave(hashes);
        console.timeEnd(savedTxMessage);
      } catch (e) {
        return;
      }
    };
    try {
      const promises = chunkedHistory.map((h) => limit(() => processChunk(h)));
      await Promise.all(promises);
    } catch (e) {
      console.error(e);
      console.error(
        `Chunk failed with total history length of ${hashesToFetch.length}`
      );
    }
    console.log("Finished chunk");
    log.info("Fetching hashes");
    hashesToFetch = await mc.getHashes({ tx: null });
    log.info("Fetched hashes");
  }
};

I also pulled every transaction (legitimate and the attackers) that called the withdraw function on the candy machines.

Of the 14,800 candy machines, 11,848 have had the withdraw function executed on them. The top accounts associated with these functions are below.

{% include image.html file="cm-top-withdrawers" alt="Top withdrawer callers" %}

Only cHfYkrVAwfEoe3Mr2GbvzpNQJboDL6AiBoFZDsf8dxj seems to be doing this maliciously - the other accounts are all calling legitimate withdraw functions.

F9fER1Cb8hmjapWGZDukzcEYshAUDbSFpbXkj9QuBaQj actually seems to have created over 2,000 candy machines, and then attempted to call withdraw on them, single handedly creating ~14% of all candy machines on Solana.

[Redacted Pending Vulnerability Disclosure]

[Redacted pending vulnerability disclosure of Solana exchange]

[Redacted Pending Vulnerability Disclosure]

[Redacted pending vulnerability disclosure of Solana exchange]

Identified Projects

I went through and fetched the public keys to all known affected projects and tried to map them back to the hacked machines. I identified 334 unique projects that were actively listed on Magic Eden, Solanart, DigitalEyez, and Solsea as being affected.

<span style="max-height: 400px; white-space: pre-line; overflow: auto; display: flex; border: 1px solid black; padding: 4px;">012Funksaicy 0xDRIP 100Radials 169 Pixel Gang 3D Flowers A Pixel Art Abstergo Aeterna Civitas Afrobubble AI: Baby Bots Aircrafts AIRDOGS Alphabet Originals Angomon Angry BaboonS Angry Bunny Club Angry Citizens AngryWorms Anti Artist Club ApexDucks Halloween Arcade '88 Art by NRG – Pop Sushi Artificial Irrelevants Autistic Reindeer Herd Baby Ape Social Club Baby Bait Baby Frogs Baby Goblin Bad Bromatoes BADBOYS BalisariNFT Bannurs Bare Bones Society: The Kingdom Of Secrets Beat Drops V1 Boat Boys BoldFrames Boopie Gen 1 Bored Ape Social Club Boss Babes Broken Robot Burger Bar bugbearz Bunny Warriors CASSETS Audio CatPunk CATPUNK OG PASS Cats Club NFT Chickenz ChihuahuaSol Classic Art Mashups Coherence Combat Women NFT Contrastive Crazy Pickles Creepy Girls Crypto Greeks Crypto Idolz - Faces CryptoCream CryptoCubs CryptoCubs Mutants Cryptone™ Cryptonic Creations CryptoRock CryptoTeds CryptZero Season 2 - Ghosts Cult of Meerkats CyberKeys Danger Valley Danuki Dojo Deadass Deeps Degen Ape Society DegenEggs Degeneggs - Gen 2 Desolates Metaverse Dessert Girls DigiLife Dinos Zone Dippy Dragons NFT Doll Society Dragon Eggs NFT Dragon Slayerz Dreamland Monkeys Element Art NFT 2D Enigma Expanses enviro Enviro Epoch Labs Ethereans Eyeballz Eyes WTF Fallen Traveler Fast Food Thugbirdz Finefolk Floppy Disk Nft Flutter Fractures G.O.A.T. Collection Galactic Goose GAMEKIDZ GANder g0 Gem Heroes Ghostface Ghostly Sols Ghoulie Gang Gremlins NFT Hallow Birds Happy Pups Hellish Party Boollons Hello World! NFT Hemp Heroes and Villains: PASS High Roller Hippo Clique HOAG play Honorary Space Bums Hot Bunnies NFT Houses Of pixel Iceland - 0xDRIP Icy Bearz NFT Idle Planets - Autumn 2021 Moon Idle Planets - Holiday 2021 Moon Infamous Apes InnerMind Intersolar iTrading_Bot Jelly Beasts Jingle Monkeys Joeian's Collection JOSEPHTAYLOR.ART: CRYSTAL BEAMS Jungle Cats Just Blocks Kitten Coup Knightdom KoreanPunkz Krunk Roach NFT Kyoudai Academy: Solana Arcade Games Labyrinth Lanabots Lazy Heroes Little Noots Los Cactus Hermanos LuchaLucha NFT Lucky Kittens LuxAI Mad Vikings Arms Collection Magic Solana Shits Make your own NFT Mark McKenna's Heroes & Villains: Origins Megumi Meta Homes Metadroids Metakatz metaSpheres MetaSpheres Mickey Degods Millionaire Apes Club Mindfolk Mini Royale: Nations - Season 1 (Premium) Mob Monkettez MogulWars Monkey Ball MonkeyBall Gen Zero My name Is Sol My Name is Sol Myopa Mystic Potion Neopets Metaverse NFT Poetry NFTrees Solana NGMIPandas Nifty Nanas NON-FUNGIBLE "BEES" Nyan Heroes OGbottles Oink Club NFT OinkClub NFT PEEPS Pengu Love Personify Pesky Ice Cube Phantom Pilgrim Society PIMP MY THUG Pirates of Sol Bay - Bottles Pirates of Sol Bay - Treasures pitcrew Pix World NFT Pixel Island NFT PixelWorms PixWorldNFT Platypusol Family Playground Waves Playground: Waves PopsicleNFT Posh Dolphs Powder Heroes Prickly Pete's Platoon - OG Cactoon Series PSY Network | PlanetZ Pudgy Pigeons Rabbit Punks Realm Kings Red paperclip RowdyRex Rug Toadz Ruled by Randomness: The Genesis SantaClaus Savage Dray by Squeak Brigade SavagesTotsys SawBunny Secret Duck Society SGF United Shadowy Super Coder Shadowy Super Coder DAO SharkBros shatteredmarble ShroomZ Slimeballz sLoot Smileys Smolpenguins Snek Gang soAlien SocksOnSolana Sol Diamond Hands Sol Lions SOL NFL PLAYER'S SOL NFL Players SOL Parasites Sol Slugs Sol Tamagotchi Sol Tapes SOLadies Solagon SolAlbums Solamids Solana Baby Monkey Business Solana Bananas Solana Birbs Solana Bros Solana Cat Gang Solana Fan The Game of Squid Solana Feline Business Solana Havana Cigar Club Solana Locks Solana Mystery Box Items Solana Mystery Items Solana Pickles Solana Reversed Monkey Business Solana Robot Business Solana Samurai Journey Solana Slugs SOLANA SUPERCAR CLUB Solana Surfers Solana Tactical RPG STACC solanabets | The Clique NFT SolArc NFT Solarnauts: Mission Bravo SolBlocks Solbusters Solccoons SolCrocos Soldalas SolDice SOLDIER RABBITS SolEmoji Solez SolFoxes SolGalaxy SolGangsta Solloons Sollyfish Solmon Solmoverse: Collection 0 Solmushies SOLNANA SolNauts SolOrbs Solryx SolSlimes SolSneakers Solsteads Surreal Estate SolStoners SolTowers Solutions Solvaders SolWatchers Soul Dogs Soulofox Space Bums Space Bums: Galaxy Mint Pass Spiderverse Spirits of Solana Squareheadz Squid Society Squirrelz Stash StratosNFT Structs Superballz Surging Bulls Synesthesia, by Labyrinth Terrarium Tanks Test Guys Test Guys Item Outpost The Assembly The Baby Boogles The Beverly Hills Car Club The Collectoooooor The Elementies The Exiled Apes The Nasty Boys The Rock theBULL by metaCOLLECTIVE TheDragonClub Thirsty Cactus Garden Party Thoughtful Folk NFT ThugDragonz Tiny Tigers Titanz ToneBox Undead Sols Vale Unleashed Rel Vampires of SOL Vampires Of SOL WallStreetPunkS Wicked Pigeon Posse Wieners Wieners Club Wildfire Native Winter Tiny Tigers Wolves On Wallstreet WOOFers World of Deities NFT WUKONGSOL Xperiment </span>

Bug Bounty

In conjunction with this vulnerability research, Metaplex has launched a bug bounty program.

<blockquote class="twitter-tweet"><p lang="en" dir="ltr">Earlier this week the <a href="https://twitter.com/metaplex?ref_src=twsrc%5Etfw">@Metaplex</a> Foundation announced a Bug Bounty program—our commitment to white-hat developers we’ve been spinning up for months.<br><br>Our first contributor, <a href="https://twitter.com/jonluca?ref_src=twsrc%5Etfw">@jonluca</a>, uncovered a vulnerability in CMv1 back in January. More below. 👇 <a href="https://t.co/sq0cjtLtTj">https://t.co/sq0cjtLtTj</a></p>— Metaplex (@metaplex) <a href="https://twitter.com/metaplex/status/1504846982954762290?ref_src=twsrc%5Etfw">March 18, 2022</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>

Timeline

Appendix

This vulnerability was discussed in Discord's and on Twitter but was not widely analyzed.

All the code for this research will be made public pending final vulnerability disclosures on various exchanges.

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