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What's up, hackers? Sumit here, aka hacksage 😌. I'm back with another wild find and a CVE. this time involving a critical flaw in a Layer 1 blockchain protocol that could have turned a major bridge reserve into a personal ATM with just a single malicious transaction.

TL;DR

I uncovered a Critical-severity logic error in the protocol's bridge release handler (apply_bridge_release_tx). Because the system didn't enforce a minimum number of validators and lacked cryptographic proof binding for release events, the "2/3rds quorum" math completely collapses when only one validator is active. An attacker can basically become a "solo king" and approve their own forged funding requests.

The vulnerability was a classic case of:

❌ Quorum Degradation (One-vote control at n=1n=1) ❌ Missing Proof Binding (No source-chain evidence required) ❌ Soft Guardrails (Warn-only alerts for high-risk states)

CVE ID: CVE-2026–41204 Severity: Critical (10.0) Reward: 10,000 on chain coins Status: Patched / Validated / Paid

THE BEGINNING ~ HOW IT ALL STARTED

While most audits focus on simple token transfers, I like to poke around the "reinsurance" components, specifically bridges. These are the high-value vaults that hold the liquidity for an entire ecosystem. My goal was to see if I could find a scenario where the consensus logic actually worked against the protocol's safety.

I wasn't looking for a memory corruption or a complex math overflow. Instead, I was hunting for a Context Failure: a situation where the rules of the game stay the same, but the game board changes in a way the developers didn't expect.

My strategy? Force the consensus to its breaking point.

INITIAL RECONNAISSANCE — BROWSING THE CODE

I dove straight into crates/*****dag-coin/src/state/engine.rs, the core of the state machine. I started by searching for how the protocol managed its validator set during periods of low activity.

That's when I found this specific piece of logic in recalculate_active_set():

/* crates/*****dag-coin/src/state/engine.rs */

// Log warning if below minimum safe validator count
if self.active_validator_set.len() < crate::constants::MIN_ACTIVE_VALIDATORS {
    // 🚩 RED FLAG: The system notes the danger but doesn't STOP it!
    tracing::warn!(
        "WARNING: Active validator count ({}) below minimum {} for BFT consensus",
        self.active_validator_set.len(),
        crate::constants::MIN_ACTIVE_VALIDATORS
    );
}

Seeing a warn! for a consensus-breaking state without a corresponding Err is like seeing a fire alarm that only prints a receipt while the building burns.

THE BREAKTHROUGH ~ THE CONSOLIDATED QUORUM

Next, I moved to the bridge release logic. In a decentralized bridge, you usually need a quorum of validators to agree that a deposit happened on the other side. But what if there's only one validator?

I looked at the threshold calculation:

/* crates/*****dag-coin/src/state/engine.rs */
// Calculate threshold: ceil(2n/3) where n = active validator count
let n = self.active_validator_set.len();
let threshold = (2 * n).div_ceil(3); 🚩 // RED FLAG: The math collapses for small n!

So the thing is If n=1n=1: ⌈(2×1)/3⌉=1⌈(2×1)/3⌉=1

Wait… that means one vote is all it takes! If you are the only one in the validator set, the "two-thirds majority" is just… you.

THE EXPLOIT CHAIN

Now, finding a quorum bug is one thing, but can we actually trigger a release for any amount we want? I checked the deposit_nonce validation to see if the system required a proof-of-deposit from the source chain.

/* crates/*****dag-coin/src/state/engine.rs */
// Replay protection ONLY - no proof binding!
let nonce_key = (tx.source_chain_id, tx.deposit_nonce);
if self.used_release_nonces.contains(&nonce_key) {
    return Err(CoinError::ValidationError("bridge release already processed..."));
}

It was worse than I thought. The system only checked if the ID had been used before — it never verified if the event was real.

The Attack:

  1. The Entry: I stake 2,000 on chain coins to become a validator.
  2. The Isolation: If the validator set is small or empty, I become the sole authority.
  3. The Forge: I submit a release request for the full bridge reserve (e.g., 300 million sats) using a random, unused nonce.
  4. The Payout: The protocol sees my 1 vote, checks the threshold (which is 1), and immediately sends the coins to my address. 💀

I validated this with a PoC that drained the entire reserve in a single block.

IMPACT ASSESSMENT — HOW BAD IS THIS?

SEVERITY RATING: CRITICAL (10.0)

Become a Medium member This was a 100% loss-of-funds scenario for the bridge.

WHAT AN ATTACKER COULD DO:

  • Drain the Vault: A single malicious validator could empty the entire bridge reserve by forging releases for high amounts and arbitrary nonces.
  • Total Trust Bypass: The cryptographic assumptions of the bridge were completely bypassed by the consensus math failure.
  • Network Paralysis: Once the bridge is drained, users can no longer withdraw their assets, leading to a total loss of trust and protocol value.

WHY THIS HAPPENED — THE ROOT CAUSE

  • Dynamic Math, Static Assumptions: The developers assumed that the 2/32/3 denominator would always be large enough to prevent unilateral control.
  • Missing Hard Floors: Critical operations should have an absolute minimum participant floor (e.g., "At least 4 validators required to bridge funds").
  • Trust without Verification: Relying on validator signatures instead of cryptographic proofs of source-chain state.

KEY TAKEAWAYS FOR RESEARCHERS

If you want to hunt for logic bugs in L1s, remember this:

  1. Question the Quorum: Always check the "extreme" ends of the consensus set. Developers rarely test the n=1n=1 case in their local dev environments.
  2. Red Flag Phasing: Look for places where state mutation (charging fees, incrementing nonces) happens before authorization checks.
  3. Bridges are Not Multisigs: A bridge should be an automated, proof-based system. If it relies only on signatures, it's just a centralized vault waiting to be drained.

REWARD & RECOGNITION

The security team acted with lightning speed to patch this and secure the bridge.

  • Reward: 10,000 on chain coins (Mainnet)
  • Status: Validated / Fixed / Fully Paid

Solving high-impact logic flaws like this is exactly why I love security research!

CLOSING WORDS 😄

Thanks for sticking with me through this deep dive! I hope this writeup inspires you to look closer at the "consensus edge cases" in your favorite protocols.

Remember: Breaking things is just half the fun — building a safer web3 is the real goal.

Catch me on Instagram @hacksagex for more bug bounty adventures, technical deep-dives, and ethical hacking content.

Stay curious. Stay ethical. Stay secure.

— Sumit Shah (HackSage)

Instagram: @hacksagex

DISCLAIMER: This research was conducted responsibly and ethically. The vulnerability is now fully patched. This writeup is for educational purposes only.

DISCLAIMER: This research was conducted ethically and reported responsibly. The vulnerability is now patched. This writeup is for educational purposes only.