[Asp.Net Core] 网站中的XSS跨站脚本攻击和防范

漏洞说明：
跨站脚本攻击(Cross Site Scripting)，为了不和层叠样式表(Cascading Style Sheets, CSS)的缩写混淆，故将跨站脚本攻击缩写为XSS。恶意攻击者往Web页面里插入恶意Web脚本代码（html、javascript、css等），当用户浏览该页面时，嵌入其中的Web脚本代码会被执行，从而达到恶意攻击用户的特殊目的。

测试步骤
访问系统网站，点击基础报告库进行编辑，使用Burp抓包并重新构造数据包

重新访问，成功触发了XSS弹窗

解决方法：

将危险内容过滤去除，用HTML转义字符串（Escape Sequence）表达的则保留
添加脚本过滤类

    /// <summary>     /// Html 脚本过滤     /// </summary>     public class NHtmlFilter     {         protected static readonly RegexOptions REGEX_FLAGS_SI = RegexOptions.IgnoreCase | RegexOptions.Singleline | RegexOptions.Compiled;          private static string P_COMMENTS = "<!--(.*?)-->";         private static Regex P_COMMENT = new Regex("^!--(.*)--$", REGEX_FLAGS_SI);         private static string P_TAGS = "<(.*?)>";         private static Regex P_END_TAG = new Regex("^/([a-z0-9]+)", REGEX_FLAGS_SI);         private static Regex P_START_TAG = new Regex("^([a-z0-9]+)(.*?)(/?)$", REGEX_FLAGS_SI);         private static Regex P_QUOTED_ATTRIBUTES = new Regex("([a-z0-9|(a-z0-9\-a-z0-9)]+)=(["'])(.*?)\2", REGEX_FLAGS_SI);         private static Regex P_UNQUOTED_ATTRIBUTES = new Regex("([a-z0-9]+)(=)([^"\s']+)", REGEX_FLAGS_SI);         private static Regex P_PROTOCOL = new Regex("^([^:]+):", REGEX_FLAGS_SI);         private static Regex P_ENTITY = new Regex("&#(\d+);?");         private static Regex P_ENTITY_UNICODE = new Regex("&#x([0-9a-f]+);?");         private static Regex P_ENCODE = new Regex("%([0-9a-f]{2});?");         private static Regex P_VALID_ENTITIES = new Regex("&([^&;]*)(?=(;|&|$))");         private static Regex P_VALID_QUOTES = new Regex("(>|^)([^<]+?)(<|$)", RegexOptions.Singleline | RegexOptions.Compiled);         private static string P_END_ARROW = "^>";         private static string P_BODY_TO_END = "<([^>]*?)(?=<|$)";         private static string P_XML_CONTENT = "(^|>)([^<]*?)(?=>)";         private static string P_STRAY_LEFT_ARROW = "<([^>]*?)(?=<|$)";         private static string P_STRAY_RIGHT_ARROW = "(^|>)([^<]*?)(?=>)";         private static string P_AMP = "&";         private static string P_QUOTE = """;         private static string P_LEFT_ARROW = "<";         private static string P_RIGHT_ARROW = ">";         private static string P_BOTH_ARROWS = "<>";          // @xxx could grow large... maybe use sesat's ReferenceMap         private static Dictionary<string, string> P_REMOVE_PAIR_BLANKS = new Dictionary<string, string>();         private static Dictionary<string, string> P_REMOVE_SELF_BLANKS = new Dictionary<string, string>();         /**           * flag determining whether to try to make tags when presented with "unbalanced"          * angle brackets (e.g. "<b text </b>" becomes "<b> text </b>").  If set to false,          * unbalanced angle brackets will be html escaped.          */         protected static bool alwaysMakeTags = true;          /**          * flag determing whether comments are allowed in input String.          */         protected static bool stripComment = true;           /// <summary>         /// 不允许         /// </summary>         private string[] vDisallowed { get; set; }         /// <summary>         /// 允许         /// </summary>         protected Dictionary<string, List<string>> vAllowed { get; set; }          /** counts of open tags for each (allowable) html element **/         protected Dictionary<string, int> vTagCounts;          /** html elements which must always be self-closing (e.g. "<img />") **/         protected string[] vSelfClosingTags;          /** html elements which must always have separate opening and closing tags (e.g. "<b></b>") **/         protected string[] vNeedClosingTags;          /** attributes which should be checked for valid protocols **/         protected string[] vProtocolAtts;          /** allowed protocols **/         protected string[] vAllowedProtocols;          /** tags which should be removed if they contain no content (e.g. "<b></b>" or "<b />") **/         protected string[] vRemoveBlanks;          /** entities allowed within html markup **/         protected string[] vAllowedEntities;           /// <summary>         /// 是否为调试         /// </summary>         protected bool vDebug;          public NHtmlFilter() : this(false) { }          public NHtmlFilter(bool debug)         {             //List<Item> vAllowed = new List<Item>();             vAllowed = new Dictionary<string, List<string>>();             #region 允许通过数组              vAllowed.Add("a", new List<string>() { "target", "href", "title", "class", "style" });             vAllowed.Add("addr", new List<string>() { "title", "class", "style" });             vAllowed.Add("address", new List<string>() { "class", "style" });             vAllowed.Add("area", new List<string>() { "shape", "coords", "href", "alt" });             vAllowed.Add("article", new List<string>() { });             vAllowed.Add("aside", new List<string>() { });             vAllowed.Add("audio", new List<string>() { "autoplay", "controls", "loop", "preload", "src", "class", "style" });             vAllowed.Add("b", new List<string>() { "class", "style" });             vAllowed.Add("bdi", new List<string>() { "dir" });             vAllowed.Add("bdo", new List<string>() { "dir" });             vAllowed.Add("big", new List<string>() { });             vAllowed.Add("blockquote", new List<string>() { "cite", "class", "style" });             vAllowed.Add("br", new List<string>() { });             vAllowed.Add("caption", new List<string>() { "class", "style" });             vAllowed.Add("center", new List<string>() { });             vAllowed.Add("cite", new List<string>() { });             vAllowed.Add("code", new List<string>() { "class", "style" });             vAllowed.Add("col", new List<string>() { "align", "valign", "span", "width", "class", "style" });             vAllowed.Add("colgroup", new List<string>() { "align", "valign", "span", "width", "class", "style" });             vAllowed.Add("dd", new List<string>() { "class", "style" });             vAllowed.Add("del", new List<string>() { "datetime" });             vAllowed.Add("details", new List<string>() { "open" });             vAllowed.Add("div", new List<string>() { "class", "style" });             vAllowed.Add("dl", new List<string>() { "class", "style" });             vAllowed.Add("dt", new List<string>() { "class", "style" });             vAllowed.Add("em", new List<string>() { "class", "style" });             vAllowed.Add("font", new List<string>() { "color", "size", "face" });             vAllowed.Add("footer", new List<string>() { });             vAllowed.Add("h1", new List<string>() { "class", "style" });             vAllowed.Add("h2", new List<string>() { "class", "style" });             vAllowed.Add("h3", new List<string>() { "class", "style" });             vAllowed.Add("h4", new List<string>() { "class", "style" });             vAllowed.Add("h5", new List<string>() { "class", "style" });             vAllowed.Add("h6", new List<string>() { "class", "style" });             vAllowed.Add("header", new List<string>() { });             vAllowed.Add("hr", new List<string>() { });             vAllowed.Add("i", new List<string>() { "class", "style" });             vAllowed.Add("img", new List<string>() { "src", "alt", "title", "style", "width", "height", "id", "_src", "loadingclass", "class", "data-latex", "data-id", "data-type", "data-s" });             vAllowed.Add("ins", new List<string>() { "datetime" });             vAllowed.Add("li", new List<string>() { "class", "style" });             vAllowed.Add("mark", new List<string>() { });             vAllowed.Add("nav", new List<string>() { });             vAllowed.Add("ol", new List<string>() { "class", "style" });             vAllowed.Add("p", new List<string>() { "class", "style" });             vAllowed.Add("pre", new List<string>() { "class", "style" });             vAllowed.Add("s", new List<string>() { });             vAllowed.Add("section", new List<string>() { });             vAllowed.Add("small", new List<string>() { });             vAllowed.Add("span", new List<string>() { "class", "style" });             vAllowed.Add("sub", new List<string>() { "class", "style" });             vAllowed.Add("sup", new List<string>() { "class", "style" });             vAllowed.Add("strong", new List<string>() { "class", "style" });             vAllowed.Add("table", new List<string>() { "width", "border", "align", "valign", "class", "style" });             vAllowed.Add("tbody", new List<string>() { "align", "valign", "class", "style" });             vAllowed.Add("td", new List<string>() { "width", "rowspan", "colspan", "align", "valign", "class", "style" });             vAllowed.Add("tfoot", new List<string>() { "align", "valign", "class", "style" });             vAllowed.Add("th", new List<string>() { "width", "rowspan", "colspan", "align", "valign", "class", "style" });             vAllowed.Add("thead", new List<string>() { "align", "valign", "class", "style" });             vAllowed.Add("tr", new List<string>() { "rowspan", "align", "valign", "class", "style" });             vAllowed.Add("tt", new List<string>() { });             vAllowed.Add("u", new List<string>() { });             vAllowed.Add("ul", new List<string>() { "class", "style" });             vAllowed.Add("video", new List<string>() { "autoplay", "controls", "loop", "preload", "src", "height", "width", "class", "style" });             #endregion               vDebug = debug;             vTagCounts = new Dictionary<string, int>();              vSelfClosingTags = new string[] { "img" };             vNeedClosingTags = new string[] { "a", "b", "strong", "i", "em" };             vDisallowed = new string[] { "script" };             vAllowedProtocols = new string[] { "http", "mailto" }; // no ftp.             vProtocolAtts = new string[] { "src", "href" };             vRemoveBlanks = new string[] { "a", "b", "strong", "i", "em" };             vAllowedEntities = new string[] { "amp", "gt", "lt", "quot" };             stripComment = true;             alwaysMakeTags = true;         }           protected void reset()         {             vTagCounts = new Dictionary<string, int>();         }          protected void debug(string msg)         {             if (vDebug)                 System.Diagnostics.Debug.WriteLine(msg);         }          //---------------------------------------------------------------         // my versions of some PHP library functions          public static string chr(int dec)         {             return "" + (char)dec;         }          /// <summary>         /// 转换成实体字符         /// </summary>         /// <param name="str"></param>         /// <returns></returns>         public static string htmlSpecialChars(string str)         {             str = str.Replace(P_QUOTE, """);              str = str.Replace(P_LEFT_ARROW, "<");             str = str.Replace(P_RIGHT_ARROW, ">");             str = str.Replace("n", "<br>");             return str;         }          //---------------------------------------------------------------          /**          * given a user submitted input String, filter out any invalid or restricted          * html.          *           * @param input text (i.e. submitted by a user) than may contain html          * @return "clean" version of input, with only valid, whitelisted html elements allowed          */         public string filter(string input)         {             reset();             string s = input;              debug("************************************************");             debug("              INPUT: " + input);              s = escapeComments(s);             debug("     escapeComments: " + s);              s = balanceHTML(s);             debug("        balanceHTML: " + s);              s = checkTags(s);             debug("          checkTags: " + s);              s = processRemoveBlanks(s);             debug("processRemoveBlanks: " + s);              s = validateEntities(s);             debug("    validateEntites: " + s);              debug("************************************************nn");             return s;         }          protected string escapeComments(string s)         {             return Regex.Replace(s, P_COMMENTS, new MatchEvaluator(ConverMatchComments), RegexOptions.Singleline);         }          protected string regexReplace(string regex_pattern, string replacement, string s)         {             return Regex.Replace(s, regex_pattern, replacement);         }          protected string balanceHTML(string s)         {             if (alwaysMakeTags)             {                 //                 // try and form html                 //                 s = regexReplace(P_END_ARROW, "", s);                 s = regexReplace(P_BODY_TO_END, "<$1>", s);                 s = regexReplace(P_XML_CONTENT, "$1<$2", s);              }             else             {                 //                 // escape stray brackets                 //                 s = regexReplace(P_STRAY_LEFT_ARROW, "<$1", s);                 s = regexReplace(P_STRAY_RIGHT_ARROW, "$1$2><", s);                  //                 // the last regexp causes '<>' entities to appear                 // (we need to do a lookahead assertion so that the last bracket can                 // be used in the next pass of the regexp)                 //                 s = s.Replace(P_BOTH_ARROWS, "");             }             return s;         }          protected string checkTags(string s)         {             //替换不允许标签             foreach (var item in vDisallowed)             {                 s = Regex.Replace(s, string.Format(@"<{0}b(.)*?>(.)+?</{0}>", item), "");             }             s = Regex.Replace(s, P_TAGS, new MatchEvaluator(ConverMatchTags), RegexOptions.Singleline);              // these get tallied in processTag             // (remember to reset before subsequent calls to filter method)             foreach (string key in vTagCounts.Keys)             {                 for (int ii = 0; ii < vTagCounts[key]; ii++)                 {                     s += "</" + key + ">";                 }             }              return s;         }          protected string processRemoveBlanks(string s)         {             foreach (string tag in vRemoveBlanks)             {                 s = regexReplace("<" + tag + "(\s[^>]*)?></" + tag + ">", "", s);                 s = regexReplace("<" + tag + "(\s[^>]*)?/>", "", s);             }             return s;         }          private string processTag(string s)         {             // ending tags             Match m = P_END_TAG.Match(s);             if (m.Success)             {                 string name = m.Groups[1].Value.ToLower();                 if (allowed(name))                 {                     if (!inArray(name, vSelfClosingTags))                     {                         if (vTagCounts.ContainsKey(name))                         {                             vTagCounts[name] = vTagCounts[name] - 1;                             return "</" + name + ">";                         }                     }                 }             }               // starting tags             m = P_START_TAG.Match(s);             if (m.Success)             {                 string name = m.Groups[1].Value.ToLower();                 string body = m.Groups[2].Value;                 string ending = m.Groups[3].Value;                  //debug( "in a starting tag, name='" + name + "'; body='" + body + "'; ending='" + ending + "'" );                 if (allowed(name))                 {                     string params1 = "";                      MatchCollection m2 = P_QUOTED_ATTRIBUTES.Matches(body);                     MatchCollection m3 = P_UNQUOTED_ATTRIBUTES.Matches(body);                     List<string> paramNames = new List<string>();                     List<string> paramValues = new List<string>();                     foreach (Match match in m2)                     {                         paramNames.Add(match.Groups[1].Value); //([a-z0-9]+)                         paramValues.Add(match.Groups[3].Value); //(.*?)                     }                     foreach (Match match in m3)                     {                         paramNames.Add(match.Groups[1].Value); //([a-z0-9]+)                         paramValues.Add(match.Groups[3].Value); //([^"\s']+)                     }                      string paramName, paramValue;                     for (int ii = 0; ii < paramNames.Count; ii++)                     {                         paramName = paramNames[ii].ToLower();                         paramValue = paramValues[ii];                          if (allowedAttribute(name, paramName))                         {                             if (inArray(paramName, vProtocolAtts))                             {                                 paramValue = processParamProtocol(paramValue);                             }                             params1 += " " + paramName + "="" + paramValue + """;                         }                     }                      if (inArray(name, vSelfClosingTags))                     {                         ending = " /";                     }                      if (inArray(name, vNeedClosingTags))                     {                         ending = "";                     }                      if (ending == null || ending.Length < 1)                     {                         if (vTagCounts.ContainsKey(name))                         {                             vTagCounts[name] = vTagCounts[name] + 1;                         }                         else                         {                             vTagCounts.Add(name, 1);                         }                     }                     else                     {                         ending = " /";                     }                     return "<" + name + params1 + ending + ">";                 }                 else                 {                     return "";                 }             }              // comments             m = P_COMMENT.Match(s);             if (!stripComment && m.Success)             {                 return "<" + m.Value + ">";             }              return "";         }          private string processParamProtocol(string s)         {             s = decodeEntities(s);             Match m = P_PROTOCOL.Match(s);             if (m.Success)             {                 string protocol = m.Groups[1].Value;                 if (!inArray(protocol, vAllowedProtocols))                 {                     // bad protocol, turn into local anchor link instead                     s = "#" + s.Substring(protocol.Length + 1, s.Length - protocol.Length - 1);                     if (s.StartsWith("#//"))                     {                         s = "#" + s.Substring(3, s.Length - 3);                     }                 }             }             return s;         }          private string decodeEntities(string s)         {              s = P_ENTITY.Replace(s, new MatchEvaluator(ConverMatchEntity));              s = P_ENTITY_UNICODE.Replace(s, new MatchEvaluator(ConverMatchEntityUnicode));              s = P_ENCODE.Replace(s, new MatchEvaluator(ConverMatchEntityUnicode));              s = validateEntities(s);             return s;         }          private string validateEntities(string s)         {             s = P_VALID_ENTITIES.Replace(s, new MatchEvaluator(ConverMatchValidEntities));             s = P_VALID_QUOTES.Replace(s, new MatchEvaluator(ConverMatchValidQuotes));             return s;         }          private static bool inArray(string s, string[] array)         {             foreach (string item in array)             {                 if (item != null && item.Equals(s))                 {                     return true;                 }             }             return false;         }          private bool allowed(string name)         {             return (vAllowed.Count == 0 || vAllowed.ContainsKey(name)) && !inArray(name, vDisallowed);         }          private bool allowedAttribute(string name, string paramName)         {             return allowed(name) && (vAllowed.Count == 0 || vAllowed[name].Contains(paramName));         }          private string checkEntity(string preamble, string term)         {              return ";".Equals(term) && isValidEntity(preamble)                     ? '&' + preamble                     : "&" + preamble;         }         private bool isValidEntity(string entity)         {             return inArray(entity, vAllowedEntities);         }         private static string ConverMatchComments(Match match)         {             string matchValue = "<!--" + htmlSpecialChars(match.Groups[1].Value) + "-->";             return matchValue;         }          private string ConverMatchTags(Match match)         {             string matchValue = processTag(match.Groups[1].Value);             return matchValue;         }          private string ConverMatchEntity(Match match)         {             string v = match.Groups[1].Value;             int decimal1 = int.Parse(v);             return chr(decimal1);         }          private string ConverMatchEntityUnicode(Match match)         {             string v = match.Groups[1].Value;             int decimal1 = Convert.ToInt32("0x" + v, 16);             return chr(decimal1);         }          private string ConverMatchValidEntities(Match match)         {             string one = match.Groups[1].Value; //([^&;]*)             string two = match.Groups[2].Value; //(?=(;|&|$))             return checkEntity(one, two);         }         private string ConverMatchValidQuotes(Match match)         {             string one = match.Groups[1].Value; //(>|^)             string two = match.Groups[2].Value; //([^<]+?)             string three = match.Groups[3].Value;//(<|$)             return one + regexReplace(P_QUOTE, """, two) + three;         }          public bool isAlwaysMakeTags()         {             return alwaysMakeTags;         }          public bool isStripComments()         {             return stripComment;         }          class Item         {             public string name { get; set; }             public List<string> parameter { get; set; }         }      } 

源代码出自：https://www.cnblogs.com/OleRookie/p/5970167.html

在请求时对参数的内容进行过滤：

var nHtmlFilter = new NHtmlFilter(false); surveyPayload.PayloadContent = nHtmlFilter.filter(surveyPayload.PayloadContent); 

再次请求时，已将危险代码转成HTML转义字符串的形式了