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协议遭到攻击，造成约19,000美元的损失。

<p>2025年4月18日，BTNFT协议遭到攻击，造成约1.9万美元的损失。</p><p>BTNFT是一个NFT合约，内置BTT代币锁仓和奖励分配机制，将NFT销售与与基于时间的代币释放机制相结合。</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><�约：br><a href="https://bscscan.com/address/0x0fc91b6fea2e7a827a8c99c91101ed36c638521b"" rel="nofollow">https://bscscan.com/address/0x0fc91b6fea2e7a827a8c99c91101ed36c638521b</a></p><p>攻击交易：<br><a href href href b.com/0/x cbff665c43f665c43f91d66a56b4aa9ba647486a5311bb0b4381de4d653a9d8237d"://can./tx/tx/0x1e90cbff665c43f f91d66a56b4aa9ba647486a5311bb0b4381de4381de46539d8237d</a></p><h2><strong>攻击分析</strong></h2><p>查看�击交�易我们可以看到�者重复调用<code>transferFrom</code>函数，试图将ID从1到500的NFT转移到BTNFT合约本身。从发出的出<code>BTT.Transfer</code>和<code>BTNFT.TokensClaimed</code>事件，我们可以确定攻击者正在从BTNFT合约收集BTT代币。</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>为了了攻击者何能这样做，让我们看看BTNFT合约中<code>transferFrom</code>函数的实现。我们可以看到它调用<code>_update</code>函数将NFT转移给新所有。</</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>查看<code>_update</code>函数的实现，当接收者是BTNFT合约本身时，它调用<code>claimReward</code>函数向调用者转移BTT代币，没有任查。这是一一个个明显的安全漏洞，何可以将NFTS转移到BTNFT合约本身并领取BTT奖励，而无需�拥有任何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>结论h</p�示了授权逻辑中的简单漏洞如何导致重大财务损失。合约的<code>_update</code>函数未能验证调用在NFT合约转移本到合约本身时是否有合法权利取奖励。这种疏忽允许任在不�实�NFT的情况下领BTT代币，造成1.9万美元的损失。这一事件凸显了在智能合约中实施适当的授权检查和输入验证的关键重要性，尤其是在处理合约自身交互和奖和奖励分配配>

BTNFT 事件 - 验证检查不当导致奖励被盗用

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BTNFT 事件 - 验证检查不当导致奖励被盗用

概述>者：https://bscscan.comn/address/0x7a4d144307d2dfa2885887368e4cd4678db3c27a<�约：br>https://bscscan.com/address/0x0fc91b6fea2e7a827a8c99c91101ed36c638521b攻击交易：

攻击分析

概述>者：
https://bscscan.comn/address/0x7a4d144307d2dfa2885887368e4cd4678db3c27a
<�约：br>https://bscscan.com/address/0x0fc91b6fea2e7a827a8c99c91101ed36c638521b
攻击交易：