[SECURITY-1774]

core/src/main/java/jenkins/security/SuspiciousRequestFilter.java

+package jenkins.security;
+
+import jenkins.util.SystemProperties;
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.NoExternalUse;
+
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import java.io.IOException;
+import java.util.logging.Logger;
+
+@Restricted(NoExternalUse.class)
+public class SuspiciousRequestFilter implements Filter {
+
+    /** System property name set to true or false to indicate whether or not semicolons should be allowed in URL paths. */
+    public static final String ALLOW_SEMICOLONS_IN_PATH = SuspiciousRequestFilter.class.getName() + ".allowSemicolonsInPath";
+    public static boolean allowSemicolonsInPath = SystemProperties.getBoolean(ALLOW_SEMICOLONS_IN_PATH, false);
+    private static final Logger LOGGER = Logger.getLogger(SuspiciousRequestFilter.class.getName());
+
+    @Override
+    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
+        HttpServletRequest httpRequest = (HttpServletRequest) request;
+        HttpServletResponse httpResponse = (HttpServletResponse) response;
+        if (!allowSemicolonsInPath && httpRequest.getRequestURI().contains(";")) {
+            LOGGER.warning(() -> "Denying HTTP " + httpRequest.getMethod() + " to " + httpRequest.getRequestURI() +
+                    " as it has an illegal semicolon in the path. This behavior can be overridden by setting the system property " +
+                    ALLOW_SEMICOLONS_IN_PATH + " to true. For more information, see https://jenkins.io/redirect/semicolons-in-urls");
+            httpResponse.sendError(HttpServletResponse.SC_BAD_REQUEST, "Semicolons are not allowed in the request URI");
+        } else {
+            chain.doFilter(request, response);
+        }
+    }
+
+    @Override
+    public void init(FilterConfig filterConfig) throws ServletException {
+    }
+
+    @Override
+    public void destroy() {
+    }
+}

test/src/test/java/hudson/security/csrf/CrumbExclusionTest.java

@@ -36,7 +36,10 @@ import hudson.model.UnprotectedRootAction;
 import jenkins.model.Jenkins;
 import static org.hamcrest.Matchers.containsString;
 
+import jenkins.security.SuspiciousRequestFilter;
+import org.junit.AfterClass;
 import org.junit.Assert;
+import org.junit.BeforeClass;
 import org.junit.Test;
 import static org.junit.Assert.*;
 import org.junit.Rule;
@@ -57,6 +60,16 @@ public class CrumbExclusionTest {
     @Rule
     public JenkinsRule r = new JenkinsRule();
 
+    @BeforeClass
+    public static void prepare() {
+        SuspiciousRequestFilter.allowSemicolonsInPath = true;
+    }
+
+    @AfterClass
+    public static void cleanup() {
+        SuspiciousRequestFilter.allowSemicolonsInPath = false;
+    }
+
     @Issue("SECURITY-1774")
     @Test
     public void pathInfo() throws Exception {

test/src/test/java/jenkins/security/SuspiciousRequestFilterTest.java

+package jenkins.security;
+
+import com.gargoylesoftware.htmlunit.WebRequest;
+import com.gargoylesoftware.htmlunit.WebResponse;
+import hudson.ExtensionList;
+import hudson.model.UnprotectedRootAction;
+import org.junit.Rule;
+import org.junit.Test;
+import org.jvnet.hudson.test.Issue;
+import org.jvnet.hudson.test.JenkinsRule;
+import org.jvnet.hudson.test.TestExtension;
+import org.kohsuke.stapler.QueryParameter;
+import org.kohsuke.stapler.verb.GET;
+
+import javax.annotation.CheckForNull;
+import javax.servlet.http.HttpServletResponse;
+import java.net.URL;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.nullValue;
+
+@Issue("SECURITY-1774")
+public class SuspiciousRequestFilterTest {
+
+    @Rule
+    public JenkinsRule j = new JenkinsRule();
+
+    private WebResponse get(String path) throws Exception {
+        return j.createWebClient()
+                .withThrowExceptionOnFailingStatusCode(false)
+                .getPage(new WebRequest(new URL(j.getURL(), path)))
+                .getWebResponse();
+    }
+
+    @Test
+    public void denySemicolonInRequestPathByDefault() throws Exception {
+        WebResponse response = get("foo/bar/..;/?baz=bruh");
+        assertThat(Foo.getInstance().baz, is(nullValue()));
+        assertThat(response.getStatusCode(), is(HttpServletResponse.SC_BAD_REQUEST));
+        assertThat(response.getContentAsString(), containsString("Semicolons are not allowed in the request URI"));
+    }
+
+    @Test
+    public void allowSemicolonsInRequestPathWhenEscapeHatchEnabled() throws Exception {
+        SuspiciousRequestFilter.allowSemicolonsInPath = true;
+        try {
+            WebResponse response = get("foo/bar/..;/..;/cli?baz=bruh");
+            assertThat(Foo.getInstance().baz, is("bruh"));
+            assertThat(response.getStatusCode(), is(HttpServletResponse.SC_OK));
+        } finally {
+            SuspiciousRequestFilter.allowSemicolonsInPath = false;
+        }
+    }
+
+    @Test
+    public void allowSemicolonsInQueryParameters() throws Exception {
+        WebResponse response = get("foo/bar?baz=foo;bar=baz");
+        assertThat(Foo.getInstance().baz, is("foo;bar=baz"));
+        assertThat(response.getStatusCode(), is(HttpServletResponse.SC_OK));
+    }
+
+    @TestExtension
+    public static class Foo implements UnprotectedRootAction {
+
+        private static Foo getInstance() {
+            return ExtensionList.lookupSingleton(Foo.class);
+        }
+
+        private String baz;
+
+        @CheckForNull
+        @Override
+        public String getIconFileName() {
+            return null;
+        }
+
+        @CheckForNull
+        @Override
+        public String getDisplayName() {
+            return "Pitied Foos";
+        }
+
+        @CheckForNull
+        @Override
+        public String getUrlName() {
+            return "foo";
+        }
+
+        @GET
+        public void doBar(@QueryParameter String baz) {
+            this.baz = baz;
+        }
+
+        @GET
+        public void doIndex(@QueryParameter String baz) {
+            this.baz = "index: " + baz;
+        }
+    }
+
+}

war/src/main/webapp/WEB-INF/web.xml

@@ -50,6 +50,11 @@ THE SOFTWARE.
     <url-pattern>/*</url-pattern>
   </servlet-mapping>
 
+  <filter>
+    <filter-name>suspicious-request-filter</filter-name>
+    <filter-class>jenkins.security.SuspiciousRequestFilter</filter-class>
+    <async-supported>true</async-supported>
+  </filter>
   <filter>
     <filter-name>diagnostic-name-filter</filter-name>
     <filter-class>org.kohsuke.stapler.DiagnosticThreadNameFilter</filter-class>
@@ -125,7 +130,11 @@ THE SOFTWARE.
     <url-pattern>*.png</url-pattern>
   </filter-mapping>
   -->
-  
+
+  <filter-mapping>
+    <filter-name>suspicious-request-filter</filter-name>
+    <url-pattern>/*</url-pattern>
+  </filter-mapping>
   <filter-mapping>
     <filter-name>diagnostic-name-filter</filter-name>
     <url-pattern>/*</url-pattern>