Deep Dive into the Truebit Vulnerability Incident: How Integer Overflow Allowed Hackers to Mint $26.44 Million at Zero Cost

January 8th, the computation verification platform Truebit suffered a major security incident. SlowMist Security Team’s analysis report revealed the truth behind the event: attackers exploited an integer overflow vulnerability in the Purchase contract to mint TRU tokens at nearly zero cost, then stole 8,535 ETH, worth approximately $26.44 million. Even more concerning, the hackers completed all money laundering through Tornado Cash between January 10-11, making recovery almost impossible. This is not only a huge economic loss but also a severe test of the entire smart contract ecosystem’s security awareness.

The Nature of the Vulnerability: The Forgotten Protection Mechanism

What is an integer overflow

An integer overflow is a common yet dangerous smart contract vulnerability. Simply put, when a numerical calculation exceeds the maximum value that its data type can represent, the system automatically “wraps around” to the minimum value. For example, if an 8-bit unsigned integer’s maximum value is 255, adding 1 causes it to become 0.

In Truebit’s Purchase contract, this vulnerability was exploited to perform price calculations. Attackers crafted transactions with carefully designed parameters, causing the price calculation to overflow, ultimately allowing the system to mint TRU tokens at an extremely low price (close to zero). This is equivalent to the attacker completing an operation that should have cost millions of dollars at almost no cost.

Why does this vulnerability occur

According to SlowMist’s analysis, the root cause is that Truebit’s contracts lack overflow protection mechanisms. This issue is a classic security risk in Solidity programming.

Truebit used contracts compiled with Solidity versions before 0.8.0, meaning all arithmetic operations required SafeMath for protection. However, evidently, at some point in the Price calculation, this protection was omitted.

Attack Path and Market Response

Hacker’s Attack Process

According to monitoring data, the execution of this attack was shockingly efficient:

• Step 1: Identify the vulnerability, craft malicious transactions
• Step 2: Mint大量TRU tokens at minimal cost
• Step 3: Use the minted tokens to extract ETH from Truebit’s liquidity pool
• Step 4: Quickly transfer funds to mixing addresses
• Step 5: Complete money laundering via Tornado Cash (done on Jan 10-11)

From discovering the vulnerability to laundering the funds took less than 72 hours. The hacker’s professionalism and speed suggest this was not a random attempt but a targeted, premeditated attack.

Market Concerns

This incident triggered a clear negative reaction in the market. According to latest data, ETH is currently priced at $3,102.47, showing weakness: down 0.03% in 24 hours and down 2.14% over 7 days. While the decline isn’t severe, the deeper concern is that investors are questioning the security of projects like the Computation Verification Protocol.

Truebit is a key infrastructure in the Layer 2 ecosystem for computation verification. Its security incident not only undermines confidence in the project itself but also raises industry-wide concerns about “how many similar vulnerabilities are still out there.”

Industry Lessons: This is Not an Isolated Incident

Why SafeMath is So Critical

SlowMist explicitly recommends in its report: for all contracts compiled with Solidity versions before 0.8.0, SafeMath must be used to protect all arithmetic operations. This is not optional but a fundamental safeguard.

The role of SafeMath is simple yet crucial: it checks for overflow on each arithmetic operation and reverts the transaction if an overflow occurs. This seemingly redundant step can prevent disasters like Truebit.

The Blind Spot in Audits

Interestingly, Truebit, as a well-funded project with solid technical capabilities, should have undergone security audits. Yet, this vulnerability was still missed. This reflects a broader industry issue:

• Auditors may overly rely on automated tools
• Insufficient awareness of risks associated with older Solidity versions
• Inadequate depth in code review

This means that even audited projects cannot guarantee 100% security.

Ongoing Threats from Mixing Services

Tornado Cash once again played the role of a “funds black hole” in this incident. Once funds are transferred into the mixer, they are nearly impossible to trace or freeze. That’s why the loss of 8,535 ETH is considered “almost unrecoverable.”

This highlights that even if law enforcement captures the hacker’s wallet address, if they transfer funds into a mixer promptly, subsequent tracing and enforcement become extremely difficult.

Summary

The Truebit incident is fundamentally a disaster caused by a forgotten basic safeguard. The loss of 8,535 ETH and $26.44 million is the surface issue; the deeper problem is:

• Version choice matters: Using older Solidity versions requires extra security awareness and protections
• SafeMath is not optional: it’s a necessary baseline defense
• Audits are not foolproof: deeper code review and risk assessment are needed
• Rapid response is critical: the speed at which hackers moved funds indicates the need for more agile emergency mechanisms

For the entire industry, this is a costly lesson. But if it can promote stricter security standards, more thorough audits, and more cautious version selection, this cost may not be entirely wasted.