Code:
/ FX-1434 / FX-1434 / 1.0 / untmp / whidbey / REDBITS / ndp / fx / src / xsp / System / Web / CrossSiteScriptingValidation.cs / 3 / CrossSiteScriptingValidation.cs
//------------------------------------------------------------------------------ //// Copyright (c) Microsoft Corporation. All rights reserved. // //----------------------------------------------------------------------------- /* * Detection of unsafe strings from the client (aee ASURT 122278 for details) * */ namespace System.Web { using System; using System.Globalization; internal static class CrossSiteScriptingValidation { private static bool IsAtoZ(char c) { return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z'); } // Per VSWhidbey 362133, we no longer check for those cases #if OBSOLETE // Detect strings like "OnFocus=" private static bool IsDangerousOnString(string s, int index) { // If the next character is not an 'n', it's safe if (s[index+1] != 'n' && s[index+1] != 'N') return false; // If the previous character is a letter, it's safe (e.g. "won") if (index > 0 && IsAtoZ(s[index-1])) return false; int len = s.Length; // Skip any number of letters, then any number of white spaces index += 2; while (index < len && IsAtoZ(s[index])) index++; while (index < len && Char.IsWhiteSpace(s[index])) index++; // If there is an equal, it's unsafe return (index < len && s[index] == '='); } // Detect strings like "javascript:" private static bool IsDangerousScriptString(string s, int index) { int len = s.Length; // Check for end of string case if (index+6 >= len) return false; // If the 's' is not followed by "cript", it's safe // We avoid calling String.Compare for perf reasons. if ((s[index+1] != 'c' && s[index+1] != 'C') || (s[index+2] != 'r' && s[index+2] != 'R') || (s[index+3] != 'i' && s[index+3] != 'I') || (s[index+4] != 'p' && s[index+4] != 'P') || (s[index+5] != 't' && s[index+5] != 'T')) return false; // Skip any number of white spaces index += 6; while (index < len && Char.IsWhiteSpace(s[index])) index++; // If there is a colon, it's unsafe return (index < len && s[index] == ':'); } // Detect "expression(". (as in style="qqq:expression(alert('Attack!'))", see ASURT 127079) private static bool IsDangerousExpressionString(string s, int index) { // Check for end of string case if (index+10 >= s.Length) return false; // If the 'e' is not followed by an "x", it's safe. // This avoids calling String.Compare in most cases ("ex?" is rare) if (s[index+1] != 'x' && s[index+1] != 'X') return false; // Check the rest of the string return (String.Compare( s, index+2, "pression(", 0, 9, true /*ignoreCase*/, CultureInfo.InvariantCulture) == 0); } #endif // OBSOLETE // Detect constructs that look like HTML tags #if OBSOLETE private static char[] startingChars = new char[] { '<', '&', '/', '*', 'o', 'O', 's', 'S' , 'e', 'E' }; #endif // OBSOLETE private static char[] startingChars = new char[] { '<', '&' }; // 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. internal 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(); int 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; } } int colonPosition = s.IndexOf(':'); if (colonPosition == -1) { return false; } return true; } internal static bool IsValidJavascriptId(string id) { return (String.IsNullOrEmpty(id) || System.CodeDom.Compiler.CodeGenerator.IsValidLanguageIndependentIdentifier(id)); } internal static bool IsDangerousString(string s, out int matchIndex) { //bool inComment = false; matchIndex = 0; for (int i=0;;) { // Look for the start of one of our patterns int 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] == '/') return true; break; case '&': // If the & is followed by a #, it's unsafe (e.g. S) if (s[n+1] == '#') return true; break; #if OBSOLETE case '/': // Look for a starting C style comment (i.e. "/*") if (s[n+1] == '*') { // Remember that we're inside a comment inComment = true; n++; } break; case '*': // If we're not inside a comment, we don't care about finding "*/". if (!inComment) break; // Look for the end of a C style comment (i.e. "*/"). If we found one, // we found a full comment, which we don't allow (VSWhidbey 228396). if (s[n+1] == '/') return true; break; case 'o': case 'O': if (IsDangerousOnString(s, n)) return true; break; case 's': case 'S': if (IsDangerousScriptString(s, n)) return true; break; case 'e': case 'E': if (IsDangerousExpressionString(s, n)) return true; break; #endif // OBSOLETE } // Continue searching i=n+1; } } } }
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