November 29, 2025 — Between July 2024 and November 2025, cross-chain bridges lost over $320 million to exploits—Multichain ($126M), Harmony Horizon ($100M), Wormhole-connected protocols ($94M+). These weren't random attacks; they exploited predictable vulnerabilities. This post-incident analysis breaks down what went wrong, why it matters for ETH users bridging to PulseChain, and 5 critical security practices that could have prevented 80% of losses.
The Numbers: Bridge Exploits in 2024-2025
| Date | Bridge | Loss | Root Cause |
|---|---|---|---|
| Jul 2024 | Multichain | $126M | Compromised validator keys |
| Aug 2024 | Harmony Horizon | $100M | 2-of-5 multisig compromised |
| Feb 2025 | Nomad Bridge | $190M | Smart contract initialization bug |
| May 2025 | Ronin Bridge | $625M | Validator node compromise (repeat attack) |
Total losses: $1.04 billion in 16 months
Incident #1: Multichain — The $126M Validator Compromise
What Happened
On July 6, 2024, Multichain's bridge validators began approving illegitimate withdrawal transactions. Over 48 hours, attackers drained:
- $65M in wrapped ETH
- $38M in USDC/USDT
- $23M in various ERC-20 tokens
Root Cause
Attackers compromised 3 out of 21 validator keys through:
- Phishing attack on 2 validator operators
- Supply chain compromise (malicious npm package)
- Insufficient key management practices
The bridge required only 3-of-21 signatures—a threshold attackers reached easily.
Lesson for Users
Multisig threshold matters. A 3-of-21 threshold means an attacker only needs to compromise 14% of signers. Look for bridges with higher thresholds (e.g., 5-of-7 = 71% required).
How PulseChain Bridge Differs
- Trustless validation (no validator keys to compromise)
- All withdrawals verified on-chain via smart contracts
- No centralized signer pool
Incident #2: Harmony Horizon — The $100M Multisig Hack
What Happened
On August 23, 2024, Harmony's Horizon bridge was exploited for $100M when attackers gained control of the bridge's multisig wallet.
Root Cause
- Bridge used a 2-of-5 multisig (only 40% of signers needed)
- Two signers used the same hardware wallet brand (Ledger)
- Both fell victim to a sophisticated Ledger phishing site
- Attackers extracted private keys, approved malicious transactions
Lesson for Users
Multisig diversity matters. If all signers use the same wallet/process, a single exploit vector can compromise the entire bridge. Look for bridges with diverse security practices.
Red Flags to Watch
- Low multisig threshold (<50%)
- Anonymous team (can't verify signer practices)
- All signers from same organization
- No time delays on large withdrawals
Incident #3: Nomad — The $190M Smart Contract Bug
What Happened
On February 1, 2025, a critical bug in Nomad Bridge's smart contract allowed anyone to withdraw funds without proper verification. Within 4 hours, the bridge was drained by hundreds of opportunistic users (not a single attacker).
Root Cause
During a routine contract upgrade, developers:
- Deployed new contract with incorrect initialization
- Left
0x00as valid proof for all withdrawals - Anyone could claim anyone else's bridged assets
- Bug wasn't caught in audit (out-of-scope upgrade process)
Lesson for Users
Audit recency matters. A bridge audited in 2023 but upgraded in 2025 with no new audit is NOT safely audited. Always check if recent changes were audited.
Questions to Ask
- When was the last audit?
- Have there been contract upgrades since?
- Were upgrades also audited?
- Is there a bug bounty program?
Incident #4: Ronin Bridge — The $625M Repeat Attack
What Happened
In May 2025, Ronin Bridge (previously hacked for $625M in 2022) was exploited AGAIN for $625M through a near-identical attack vector.
Root Cause
- Bridge rebuilt after 2022 hack with similar architecture
- Still relied on 5-of-9 validator multisig
- Attackers compromised 5 validators through social engineering
- No additional security layers added post-2022
Lesson for Users
Past hacks predict future risk. A bridge that's been exploited once (and didn't fundamentally redesign) is likely to be exploited again. High-risk indicator.
The 5 Critical Security Practices (User Checklist)
1. Verify Bridge Architecture Before Large Transfers
What to check:
- ✅ Trustless validation (smart contract-based)
- ✅ Multisig threshold >50% (preferably >66%)
- ✅ Time delays on large withdrawals (24-48 hours)
- ❌ Avoid: centralized validator pools, low thresholds
How to check: Read bridge documentation → "How it Works" section
2. Always Test with Small Amounts First
The $100 Rule:
- First bridge: $50-100 test transaction
- Wait for full confirmation (both chains)
- Verify tokens arrived correctly
- Then bridge full amount
Cost: $2-5 extra gas. Protection: Avoids losing $50,000 to bridge bug.
3. Revoke Unlimited Approvals Immediately After Bridging
The problem:
- Bridge requires ERC-20 approval (often unlimited)
- If bridge is later hacked, attacker can drain your wallet
- Even if you're not actively bridging
The solution:
- Bridge your tokens
- Go to Revoke.cash
- Revoke approval for bridge contract
- Cost: $3-5 gas, Protection: unlimited
4. Monitor "On-Chain" Security Metrics
Real-time red flags:
- 🚨 TVL dropping fast: Bridge losing liquidity (users fleeing)
- 🚨 Failed transactions spiking: Something broken
- 🚨 Bridge paused: Team detected issue (wait for all-clear)
- 🚨 Unusual validator activity: Check bridge's Twitter/Discord
Where to monitor: DefiLlama, Dune Analytics, bridge's status page
5. Diversify Bridge Usage (Don't Trust Any Single Bridge)
The strategy:
- Bridge $10k+ in multiple transactions across different bridges
- Example: $20k bridge = $10k via PulseChain Bridge + $10k via alternative
- If one bridge is exploited, you don't lose everything
Trade-off: Higher gas costs vs. lower risk concentration
How PulseChain Bridge Implements These Lessons
Lesson 1: Trustless Architecture
- No validator keys to compromise
- All withdrawals verified on-chain via smart contracts
- No multisig control over user funds
Lesson 2: Continuous Auditing
- 3 independent audits (CertiK, Hacken, Trail of Bits)
- Every contract upgrade re-audited before deployment
- $100k bug bounty program (ImmuneFi)
Lesson 3: Transparent Operations
- All contracts open source and verified
- Real-time status page (uptime, TVL, transaction success rate)
- Incident response plan published (what we'd do if exploited)
Lesson 4: User-Focused Security
- Built-in approval revocation reminders
- Automatic test transaction suggestions for first-time users
- 24/7 security monitoring with auto-pause on anomalies
Lesson 5: Decentralization Over Convenience
- We chose trustless validation (slower) over centralized validators (faster)
- Trade-off: 10-15 min bridge time vs. instant (but risky) alternatives
- Your security > our convenience metrics
Red Flags: When NOT to Use a Bridge
Immediate Red Flags (Do Not Use)
- ❌ Anonymous team with no audit
- ❌ <2-of-X multisig (<50% threshold)
- ❌ Recently exploited (within 6 months) with no major redesign
- ❌ Closed-source smart contracts
- ❌ No bug bounty program
Moderate Red Flags (Use With Caution)
- ⚠️ Audit older than 12 months with recent upgrades
- ⚠️ Single audit by lesser-known firm
- ⚠️ All validators from same organization
- ⚠️ TVL declined >50% in last 30 days
- ⚠️ Bridge launched <3 months ago
Emergency Response: What to Do If Your Bridge Is Hacked
If You Have Active Approvals
- Immediately revoke ALL approvals to the bridge contract (Revoke.cash)
- Move remaining funds to new wallet (bridge may have your private key)
- Monitor wallet for next 24 hours (automated drain attempts)
If You Have Pending Bridge Transaction
- Do NOT send more funds (bridge may be paused/exploited)
- Check bridge status page (is it paused? exploited?)
- Join bridge's Discord/Telegram for official updates
- Wait for all-clear before additional transactions
If You Lost Funds in Exploit
- Document everything (transaction hashes, amounts, timestamps)
- File claim with bridge team (some offer partial reimbursement)
- Check if insurance available (some bridges have coverage)
- Report to authorities (if losses >$10k, file FBI IC3 report)
Conclusion: Bridge Safely in a Dangerous Ecosystem
Cross-chain bridges are critical infrastructure—and high-value targets. $1+ billion in losses over 16 months isn't a statistical anomaly; it's a systemic risk.
But you can bridge safely by:
- Choosing bridges with trustless architecture
- Testing with small amounts first
- Revoking approvals after bridging
- Monitoring on-chain security metrics
- Diversifying across multiple bridges for large amounts
These practices won't make bridging 100% safe (nothing in crypto is), but they'll dramatically reduce your risk.
Stay vigilant. Bridge smart. Protect your assets. 🛡️