8000 [26.8] Prevent kcSanitize bypass that reactivates URLs with JavaScript scheme on the login page by michalvavrik · Pull Request #53969 · keycloak/keycloak · GitHub
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[26.8] Prevent kcSanitize bypass that reactivates URLs with JavaScript scheme on the login page #53969

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Merged
rmartinc merged 1 commit into from
Oct 14, 2026
Merged

[26.8] Prevent kcSanitize bypass that reactivates URLs with JavaScript scheme on the login page #53969

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42 changes: 40 additions & 2 deletions services/src/main/java/org/keycloak/theme/KeycloakSanitizerMethod.java
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@
import freemarker.template.TemplateMethodModelEx;
import freemarker.template.TemplateModelException;
import org.owasp.html.Encoding;
import org.owasp.html.FilterUrlByProtocolAttributePolicy;

/**
* Allows sanitizing of html that uses Freemarker ?no_esc. This way, html
Expand All @@ -33,7 +34,12 @@
public class KeycloakSanitizerMethod implements TemplateMethodModelEx {

private static final Pattern HREF_PATTERN = Pattern.compile("\\s+href=\"([^\"]*)\"");


private static final Pattern NUMERIC_ENTITY = Pattern.compile("&#([xX][0-9a-fA-F]+|[0-9]+);?");

private static final FilterUrlByProtocolAttributePolicy URL_PROTOCOL_POLICY =
new FilterUrlByProtocolAttributePolicy(List.of("http", "https", "mailto"));

@Override
public Object exec(List list) throws TemplateModelException {
if ((list.isEmpty()) || (list.get(0) == null)) {
Expand Down Expand Up @@ -80,6 +86,9 @@ private String fixURLs(String msg) {
String href = matcher.group(1).replaceAll("=", "=")
.replaceAll("\\.\\.", ".")
.replaceAll("&", "&");
if (hasDisallowedScheme(href)) {
href = "";
}
result.append(msg.substring(last, matcher.start(1))).append(href);
last = matcher.end(1);
} while (matcher.find());
Expand All @@ -88,5 +97,34 @@ private String fixURLs(String msg) {
}
return msg;
}


private boolean hasDisallowedScheme(String href) {
return URL_PROTOCOL_POLICY.apply("a", "href", decodeNumericEntities(href)) == null;
}

private String decodeNumericEntities(String value) {
Matcher matcher = NUMERIC_ENTITY.matcher(value);
StringBuilder result = new StringBuilder(value.length());
int last = 0;
while (matcher.find()) {
result.append(value, last, matcher.start());
String digits = matcher.group(1);
try {
int codePoint = (digits.charAt(0) == 'x' || digits.charAt(0) == 'X')
? Integer.parseInt(digits.substring(1), 16)
: Integer.parseInt(digits);
if (Character.isValidCodePoint(codePoint)) {
result.appendCodePoint(codePoint);
} else {
result.append(matcher.group());
}
} catch (NumberFormatException e) {
result.append(matcher.group());
}
last = matcher.end();
}
result.append(value, last, value.length());
return result.toString();
}

}
55 changes: 55 additions & 0 deletions services/src/test/java/org/keycloak/theme/KeycloakSanitizerTest.java
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Expand Up @@ -118,6 +118,61 @@ public void testUrls() throws Exception {
assertResult("<p><a href=\"https://localhost?key=123&msg=abc\" rel=\"nofollow\">link1</a><a href=\"https://localhost?key=abc&msg=123\" rel=\"nofollow\">link2</a></p>", html);
}

@Test
public void testJavascriptUrlViaNumericCharacterReferenceIsNeutralized() throws Exception {
List<String> html = new ArrayList<>();

html.add("<a href=\"javascript&#58alert(xss)\">link</a>");
assertResult("<a href=\"\" rel=\"nofollow\">link</a>", html);

html.set(0, "<a href=\"javascript&#x3aprompt(xss)\">link</a>");
assertResult("<a href=\"\" rel=\"nofollow\">link</a>", html);

html.set(0, "<a href=\"javascript&#X3Aprompt(xss)\">link</a>");
assertResult("<a href=\"\" rel=\"nofollow\">link</a>", html);

html.set(0, "<a href=\"javascript&#0000058alert(xss)\">link</a>");
assertResult("<a href=\"\" rel=\"nofollow\">link</a>", html);

html.set(0, "<a href=\"JaVaScRiPt&#58alert(xss)\">link</a>");
assertResult("<a href=\"\" rel=\"nofollow\">link</a>", html);

html.set(0, "<a href=\"java&#115cript&#58alert(xss)\">link</a>");
assertResult("<a href=\"\" rel=\"nofollow\">link</a>", html);

html.set(0, "<a href=\"java&#10script&#58alert(xss)\">link</a>");
assertResult("<a href=\"\" rel=\"nofollow\">link</a>", html);

html.set(0, "<a href=\"java&#9script&#58alert(xss)\">link</a>");
assertResult("<a href=\"\" rel=\"nofollow\">link</a>", html);

html.set(0, "<a href=\"vbscript&#58msgbox(xss)\">link</a>");
assertResult("<a href=\"\" rel=\"nofollow\">link</a>", html);

html.set(0, "<a href=\"data&#58text/plain,hello\">link</a>");
assertResult("<a href=\"\" rel=\"nofollow\">link</a>", html);

html.set(0, "<a href=\"javascript&#58;alert(xss)\">link</a>");
assertResult("link", html);

html.set(0, "<a href=\"javascript&colon;alert(xss)\">link</a>");
assertResult("link", html);
}

@Test
public void testLegitimateMarkupAndLinksArePreserved() throws Exception {
List<String> html = new ArrayList<>();

html.add("<b>ACME Corp</b>");
assertResult("<b>ACME Corp</b>", html);

html.set(0, "<a href=\"https://www.example.org/welcome\">Welcome</a>");
assertResult("<a href=\"https://www.example.org/welcome\" rel=\"nofollow\">Welcome</a>", html);

html.set(0, "<a href=\"https://kc.example.org/realms/r/login-actions/action-token?key=abc.def&client_id=account&tab_id=x1\">verify</a>");
assertResult("<a href=\"https://kc.example.org/realms/r/login-actions/action-token?key=abc.def&client_id=account&tab_id=x1\" rel=\"nofollow\">verify</a>", html);
}

private void assertResult(String expectedResult, List<String> html) throws Exception {
String result = kcEscape.exec(html).toString();
assertEquals(expectedResult, result);
Expand Down
90 changes: 90 additions & 0 deletions ...base/src/test/java/org/keycloak/tests/forms/LoginPageDisplayNameHtmlSanitizationTest.java
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@@ -0,0 +1,90 @@
package org.keycloak.tests.forms;

import org.keycloak.testframework.annotations.InjectRealm;
import org.keycloak.testframework.annotations.KeycloakIntegrationTest;
import org.keycloak.testframework.oauth.OAuthClient;
import org.keycloak.testframework.oauth.annotations.InjectOAuthClient;
import org.keycloak.testframework.realm.ManagedRealm;
import org.keycloak.testframework.ui.annotations.InjectPage;
import org.keycloak.testframework.ui.annotations.InjectWebDriver;
import org.keycloak.testframework.ui.page.LoginPage;
import org.keycloak.testframework.ui.webdriver.ManagedWebDriver;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
import org.openqa.selenium.JavascriptExecutor;

@KeycloakIntegrationTest
public class LoginPageDisplayNameHtmlSanitizationTest {

@InjectRealm
ManagedRealm managedRealm;

@InjectOAuthClient
OAuthClient oauth;

@InjectWebDriver
ManagedWebDriver driver;

@InjectPage
LoginPage loginPage;

@Test
public void decimalNumericCharacterReferenceJavascriptUrlIsNeutralized() {
String page = renderLoginPageWithDisplayNameHtml("<a href=\"javascript&#58alert(xss53813)\">pwn</a>");
assertNoExecutableScheme(page);
}

@Test
public void hexNumericCharacterReferenceJavascriptUrlIsNeutralized() {
String page = renderLoginPageWithDisplayNameHtml("<a href=\"javascript&#x3aprompt(xss53813)\">pwn</a>");
assertNoExecutableScheme(page);
}

@Test
public void legitimateDisplayNameHtmlIsPreserved() {
String page = renderLoginPageWithDisplayNameHtml("<b>ACME53813</b>");
Assertions.assertTrue(page.contains("<b>ACME53813</b>"), "benign display name markup must render");
}

@Test
public void httpLinkIsPreserved() {
String page = renderLoginPageWithDisplayNameHtml("<a href=\"http://acme53813.example.com/help?topic=sso&lang=en\">Help</a>");
Assertions.assertTrue(page.contains("<a href=\"http://acme53813.example.com/help?topic=sso&lang=en\" rel=\"nofollow\">Help</a>"),
"http link must be preserved");
}

@Test
public void httpsLinkIsPreserved() {
String page = renderLoginPageWithDisplayNameHtml("<a href=\"https://acme53813.example.com/help?topic=sso&lang=en\">Help</a>");
Assertions.assertTrue(page.contains("<a href=\"https://acme53813.example.com/help?topic=sso&lang=en\" rel=\"nofollow\">Help</a>"),
"https link must be preserved");
}

@Test
public void mailtoLinkIsPreserved() {
String page = renderLoginPageWithDisplayNameHtml("<a href=\"mailto:support@acme53813.example.com\">Mail</a>");
Assertions.assertTrue(page.contains("<a href=\"mailto:support&#64;acme53813.example.com\" rel=\"nofollow\">Mail</a>"),
"mailto link must be preserved");
}

private String renderLoginPageWithDisplayNameHtml(String displayNameHtml) {
managedRealm.updateWithCleanup(r -> r.update(realm -> realm.setDisplayNameHtml(displayNameHtml)));
oauth.openLoginForm();
loginPage.assertCurrent();
String loginPageUrl = driver.getCurrentUrl();
return (String) ((JavascriptExecutor) driver.driver()).executeScript(
"var xhr = new XMLHttpRequest();" +
"xhr.open('GET', arguments[0], false);" +
"xhr.send();" +
"return xhr.responseText;", loginPageUrl);
}

private void assertNoExecutableScheme(String pageSource) {
String lower = pageSource.toLowerCase();
Assertions.assertFalse(lower.contains("javascript&#"),
"login page must not emit a reactivated javascript URL");
Assertions.assertFalse(lower.contains("javascript:alert") || lower.contains("javascript:prompt"),
"login page must not emit a live javascript URL");
}
}
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