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Fix reflected XSS in Cross Site Scripting Challenge 6 (attribute breakout via 2nd quote/angle-bracket) #341

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Fix reflected XSS in Cross Site Scripting Challenge 6 (attribute breakout via 2nd quote/angle-bracket) #341

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11 changes: 8 additions & 3 deletions src/main/java/utils/XssFilter.java
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Original file line number Diff line number Diff line change
Expand Up @@ -40,13 +40,18 @@ public static String anotherBadUrlValidate(String input) {
input = input.toLowerCase();
if (input.startsWith("http")) {
try {
// Every occurrence of an attribute-breakout character must be neutralised, not just the
// first one - a second, un-escaped '<' / '>' / '"' / '\'' later in the string still lets
// an attacker close the surrounding href="" attribute and inject a fresh HTML attribute
// (e.g. onmouseover=alert(1)) or a whole new tag.
URL theUrl =
new URL(
input
.replaceAll("#", "&#x23;")
.replaceFirst("<", "&#x3c;")
.replaceFirst(">", "&#x3e;")
.replaceFirst("\"", "&quot;"));
.replaceAll("<", "&#x3c;")
.replaceAll(">", "&#x3e;")
.replaceAll("\"", "&quot;")
.replaceAll("'", "&#x27;"));
input = theUrl.toString();
} catch (MalformedURLException e) {
log.debug("Could not Cast URL from input: " + e.toString());
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