On April 18, 2025, the BTNFT protocol was exploited, resulting in a loss of approximately $19K.

<p>On April 18, 2025, the BTNFT protocol was exploited, resulting in a loss of approximately $19K.</p><p>BTNFT is an NFT contract with built-in BTT token vesting and reward distribution that combines NFT sales with a time-based token release mechanism.</p><h2>Overview</h2><p>Attacker: <br><a href="https://bscscan.com/address/0x7a4d144307d2dfa2885887368e4cd4678db3c27a" rel="nofollow">https://bscscan.com/address/0x7a4d144307d2dfa2885887368e4cd4678db3c27a</a></p><p>Vulnerable Contract:<br><a href="https://bscscan.com/address/0x0fc91b6fea2e7a827a8c99c91101ed36c638521b" rel="nofollow">https://bscscan.com/address/0x0fc91b6fea2e7a827a8c99c91101ed36c638521b</a></p><p>Attack Transaction:<br><a href="https://bscscan.com/tx/0x1e90cbff665c43f91d66a56b4aa9ba647486a5311bb0b4381de4d653a9d8237d" rel="nofollow">https://bscscan.com/tx/0x1e90cbff665c43f91d66a56b4aa9ba647486a5311bb0b4381de4d653a9d8237d</a></p><h2><strong>Exploit Analysis</strong></h2><p>Looking at the attack transaction, we can see that the attacker is calling the <code>transferFrom</code> function repeatedly, trying to transfer NFTs with IDs ranging from 1 to 500 to the BTNFT contract itself. From the emitted <code>BTT.Transfer</code> and <code>BTNFT.TokensClaimed</code> events, we can determine that the attacker is collecting BTT tokens from the BTNFT contract.</p><div><figure><a href="https://substackcdn.com/image/fetch/f_auto,q_auto:good,fl_progressive:steep/https%3A%2F%2Fsubstack-post-media.s3.amazonaws.com%2Fpublic%2Fimages%2F387e1239-8ccd-492b-b8ad-9308cd22dbf9_1647x810.png" rel="nofollow"><div><picture><source><img src="https://static.fwimg.io/img/feed/fda0112930fe49eb859ff9a0c8b9acd6.jpg" alt=""></source></picture><div><div><div></div><div></div></div></div></div></a></figure></div><p>To understand why the attacker was able to do this, let's take a look at the implementation of the <code>transferFrom</code> function in the BTNFT contract. We can see that it calls the <code>_update</code> function to transfer the NFTs to the new owner.</p><div><figure><a href="https://substackcdn.com/image/fetch/f_auto,q_auto:good,fl_progressive:steep/https%3A%2F%2Fsubstack-post-media.s3.amazonaws.com%2Fpublic%2Fimages%2F4a42c14c-120b-434c-8701-5a5ce9e91cfd_868x286.png" rel="nofollow"><div><picture><source><img src="https://static.fwimg.io/img/feed/c89de5b33dfd0fc2545b2db8f98322e9.jpg" alt=""></source></picture><div><div><div></div><div></div></div></div></div></a></figure></div><p>Looking at the implementation of the <code>_update</code> function, when the receiver is the BTNFT contract itself, it calls the <code>claimReward</code> function to transfer BTT tokens to the caller without any checks. This is a clear security vulnerability that allows anyone to transfer BTNFTs to the BTNFT contract itself and claim BTT rewards without actually owning any BTNFTs.</p><div><figure><a href="https://substackcdn.com/image/fetch/f_auto,q_auto:good,fl_progressive:steep/https%3A%2F%2Fsubstack-post-media.s3.amazonaws.com%2Fpublic%2Fimages%2F99767a1b-e6ab-4566-b0b5-f4146604ed22_957x541.png" rel="nofollow"><div><picture><source><img src="https://static.fwimg.io/img/feed/6e6f7d68170997f8e152a4c7dd4bbb24.jpg" alt=""></source></picture><div><div><div></div><div></div></div></div></div></a></figure></div><h2>Conclusion</h2><p>This exploit demonstrates how a simple logic bug in authorization can lead to significant financial losses. The contract's <code>_update</code> function failed to verify if the caller had legitimate rights to claim rewards when NFTs were transferred to the contract itself. This oversight allowed anyone to claim BTT tokens without actually owning any NFTs, resulting in a $19K loss. The incident highlights the critical importance of implementing proper authorization checks and input validation in smart contracts, especially when handling contract self-interactions and reward distributions.</p>

BTNFT Incident - Improper Validation Check Leads to Unauthorized Reward Claim

2025年4月18日，BTNFT協議遭到攻擊，造成約19,000美元的損失。

<p>2025年4月18日，BTNFT協議遭到攻擊，造成約1.9萬美元的損失。</p><p>BTNFT是一個NFT合約，內建BTT代幣鎖倉和獎勵分配機制，將NFT銷售與與基於時間的代幣釋放機制相結合。</p><h2>概述</h2</h2>>者：<br br><a href="https://bscs/address/0x/0x7a4d144307d2dfa2885887368e4cd4678db3c27a" rel="nofollow">https://bscscan.comn/address/0x7a4d144307d2dfa2885887368e4cd4678db3c27a</a></p><p p><�約：br><a href="https://bscscan.com/address/0x0fc91b6fea2e7a827a8c99c91101ed36c638521b"" rel="nofollow">https://bscscan.com/address/0x0fc91b6fea2e7a827a8c99c91101ed36c638521b</a></p><p>攻擊交易：<br><a href href href b.com/0/x cbff665c43f665c43f91d66a56b4aa9ba647486a5311bb0b4381de4d653a9d8237d"://can./tx/tx/0x1e90cbff665c43f f91d66a56b4aa9ba647486a5311bb0b4381de4381de46539d8237d</a></p><h2><strong>攻擊分析</strong></h2><p>檢視�擊交�易我們可以看到�者重複呼叫<code>transferFrom</code>函式，試圖將ID從1到500的NFT轉移到BTNFT合約本身。從發出的出<code>BTT.Transfer</code>和<code>BTNFT.TokensClaimed</code>事件，我們可以確定攻擊者正在從BTNFT合約收集BTT代幣。</p><div><figure><a href="https://substackcdn.com/image/fetch/f_auto,q_auto:good,fl_progressive:steep/https%3A%2F%2Fsubstack-post-media.s3.amazonaws.com%2Fpublic%2Fimages%2F387e1239-8ccd-492b-b8ad-9308cd22dbf9_1647x810.png" rel="nofollow"><div><picture><source><img src="https://static.fwimg.io/img/feed/fda0112930fe49eb859ff9a0c8b9acd6.jpg" alt=""></source></picture><div><div><div></div><div></div></div></div></div></a></figure></div><p>為了了攻擊者何能這樣做，讓我們看看BTNFT合約中<code>transferFrom</code>函式的實現。我們可以看到它呼叫<code>_update</code>函式將NFT轉移給新所有。</</p><div><figure><a href="https://substackcdn.com/image/fetch/f_auto,q_auto:good,fl_progressive:steep/https%3A%2F%2Fsubstack-post-media.s3.amazonaws.com%2Fpublic%2Fimages%2F4a42c14c-120b-434c-8701-5a5ce9e91cfd286.png" rel="nofollow"><div><picture><source><img src="https://static.fwimg.io/img/feed/c89de5b33dfd0fc2545b2db8f98322e9.jpg" alt=""></source></picture><div><div><div></div><div></div></div></div></div></a></figure></div><p>檢視<code>_update</code>函式的實現，當接收者是BTNFT合約本身時，它呼叫<code>claimReward</code>函式向呼叫者轉移BTT代幣，沒有任查。這是一一個個明顯的安全漏洞，何可以將NFTS轉移到BTNFT合約本身並領取BTT獎勵，而無需�擁有任何BTNFT。。</p<div><div><figure2><a href="https://substackcdn.com/image/fetch/f_auto,q_auto:good,fl_progressive:steep/https%3A%2F%2Fsubstack-post-media.s3.amazonaws.com%2Fpublic%2Fimages%2F99767a1b-e6ab-4566-b0b5-f4146604ed22_957x541.png" rel="nofollow"><div><picture><source><img src="https://static.fwimg.io/img/feed/6e6f7d68170997f8e152a4c7dd4bbb24.jpg" alt=""></source></picture><div><div><div></div><div></div></div></div></div></a></figure></2>結論h</p�示了授權邏輯中的簡單漏洞如何導致重大財務損失。合約的<code>_update</code>函式未能驗證呼叫在NFT合約轉移本到合約本身時是否有合法權利取獎勵。這種疏忽允許任在不�實�NFT的情況下領BTT代幣，造成1.9萬美元的損失。這一事件凸顯了在智慧合約中實施適當的授權檢查和輸入驗證的關鍵重要性，尤其是在處理合約自身互動和獎和獎勵分配配>

BTNFT 事件 - 驗證檢查不當導致獎勵被盜用

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BTNFT 事件 - 驗證檢查不當導致獎勵被盜用

概述>者：https://bscscan.comn/address/0x7a4d144307d2dfa2885887368e4cd4678db3c27a<�約：br>https://bscscan.com/address/0x0fc91b6fea2e7a827a8c99c91101ed36c638521b攻擊交易：

攻擊分析

概述>者：
https://bscscan.comn/address/0x7a4d144307d2dfa2885887368e4cd4678db3c27a
<�約：br>https://bscscan.com/address/0x0fc91b6fea2e7a827a8c99c91101ed36c638521b
攻擊交易：