Question

这是Json有效负载的Web API（因此没有Razor）。
我正在使用ASP.NET Core 2.1

首先，我要提到的是我正在用HtmlEncoder清理相关输入。但是，以防万一任何人通过我的验证器，我想在这里询问。

我想编写一个验证器，该验证器将返回错误代码，当用户尝试在输入中包含html字符串时（使用移动应用程序，这将是json负载中的属性）。

我在SO上看到过一些幼稚的实现建议-通常只是检查字符串是否包含'<'或'>'（也许还有一个或两个其他字符）。

我想我想知道这是否足以解决当前的任务。用户没有理由在此域中发布任何类型的html / xml。

周围的许多库都会清理输入。但是它们似乎都没有一个告诉您字符串是否包含潜在有害输入的方法。

正如我所说，我已经在消毒（作为最后一道防线）。但是理想情况下，我会先返回一个错误代码。

谢谢

Answer 1

使用Microsoft ASP.NET Core 1中的此类

// <copyright file="CrossSiteScriptingValidation.cs" company="Microsoft">
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>
public static class CrossSiteScriptingValidation
{
    private static readonly char[] StartingChars = { '<', '&' };

    #region Public methods

    // Only accepts http: and https: protocols, and protocolless urls.
    // Used by web parts to validate import and editor input on Url properties. 
    // Review: is there a way to escape colon that will still be recognized by IE?
    // %3a does not work with IE.
    public static bool IsDangerousUrl(string s)
    {
        if (string.IsNullOrEmpty(s))
        {
            return false;
        }

        // Trim the string inside this method, since a Url starting with whitespace
        // is not necessarily dangerous.  This saves the caller from having to pre-trim 
        // the argument as well.
        s = s.Trim();

        var len = s.Length;

        if ((len > 4) &&
            ((s[0] == 'h') || (s[0] == 'H')) &&
            ((s[1] == 't') || (s[1] == 'T')) &&
            ((s[2] == 't') || (s[2] == 'T')) &&
            ((s[3] == 'p') || (s[3] == 'P')))
        {
            if ((s[4] == ':') || ((len > 5) && ((s[4] == 's') || (s[4] == 'S')) && (s[5] == ':')))
            {
                return false;
            }
        }

        var colonPosition = s.IndexOf(':');
        return colonPosition != -1;
    }

    public static bool IsValidJavascriptId(string id)
    {
        return (string.IsNullOrEmpty(id) || System.CodeDom.Compiler.CodeGenerator.IsValidLanguageIndependentIdentifier(id));
    }

    public static bool IsDangerousString(string s, out int matchIndex)
    {
        //bool inComment = false;
        matchIndex = 0;

        for (var i = 0; ;)
        {

            // Look for the start of one of our patterns 
            var n = s.IndexOfAny(StartingChars, i);

            // If not found, the string is safe
            if (n < 0) return false;

            // If it's the last char, it's safe 
            if (n == s.Length - 1) return false;

            matchIndex = n;

            switch (s[n])
            {
                case '<':
                    // If the < is followed by a letter or '!', it's unsafe (looks like a tag or HTML comment)
                    if (IsAtoZ(s[n + 1]) || s[n + 1] == '!' || s[n + 1] == '/' || s[n + 1] == '?') return true;
                    break;
                case '&':
                    // If the & is followed by a #, it's unsafe (e.g. S) 
                    if (s[n + 1] == '#') return true;
                    break;

            }

            // Continue searching
            i = n + 1;
        }
    }

    #endregion

    #region Private methods

    private static bool IsAtoZ(char c)
    {
        return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
    }

    #endregion
}

然后使用此中间件控制URL，查询参数和内容：

public class XssMiddleware
{
    private readonly RequestDelegate _next;

    public XssMiddleware(RequestDelegate next)
    {
        if (next == null)
        {
            throw new ArgumentNullException(nameof(next));
        }

        _next = next;
    }       

    public async Task Invoke(HttpContext context)
    {
        // Check XSS in URL
        if (!string.IsNullOrWhiteSpace(context.Request.Path.Value))
        {
            var url = context.Request.Path.Value;

            int matchIndex;
            if (CrossSiteScriptingValidation.IsDangerousString(url, out matchIndex))
            {

                throw new CrossSiteScriptingException("YOUR_ERROR_MESSAGE");
            }
        }

        // Check XSS in query string
        if (!string.IsNullOrWhiteSpace(context.Request.QueryString.Value))
        {
            var queryString = WebUtility.UrlDecode(context.Request.QueryString.Value);

            int matchIndex;
            if (CrossSiteScriptingValidation.IsDangerousString(queryString, out matchIndex))
            {

                throw new CrossSiteScriptingException("YOUR_ERROR_MESSAGE");

            }
        }

        // Check XSS in request content
        var originalBody = context.Request.Body;
        try
        {                
            var content = await ReadRequestBody(context);

            int matchIndex;
            if (CrossSiteScriptingValidation.IsDangerousString(content, out matchIndex))
            {
                throw new CrossSiteScriptingException("YOUR_ERROR_MESSAGE");
            }

            await _next(context);
        }
        finally
        {
            context.Request.Body = originalBody;
        }            
    }

    private static async Task<string> ReadRequestBody(HttpContext context)
    {
        var buffer = new MemoryStream();
        await context.Request.Body.CopyToAsync(buffer);
        context.Request.Body = buffer;
        buffer.Position = 0;

        var encoding = Encoding.UTF8;
        var contentType = context.Request.GetTypedHeaders().ContentType;
        if (contentType?.Charset != null) encoding = Encoding.GetEncoding(contentType.Charset);

        var requestContent = await new StreamReader(buffer, encoding).ReadToEndAsync();
        context.Request.Body.Position = 0;

        return requestContent;
    }
}

在Xss攻击中引发异常

1 个答案: