diff --git a/java/ql/lib/semmle/code/java/frameworks/owasp/Esapi.qll b/java/ql/lib/semmle/code/java/frameworks/owasp/Esapi.qll
new file mode 100644
index 00000000000..19cabda7073
--- /dev/null
+++ b/java/ql/lib/semmle/code/java/frameworks/owasp/Esapi.qll
@@ -0,0 +1,40 @@
+/** Classes and predicates for reasoning about the `owasp.easpi` package. */
+
+import java
+
+/**
+ * The `org.owasp.esapi.Validator` interface.
+ */
+class EsapiValidator extends RefType {
+  EsapiValidator() { this.hasQualifiedName("org.owasp.esapi", "Validator") }
+}
+
+/**
+ * The methods of `org.owasp.esapi.Validator` which validate data.
+ */
+class EsapiIsValidMethod extends Method {
+  EsapiIsValidMethod() {
+    this.getDeclaringType() instanceof EsapiValidator and
+    this.hasName([
+        "isValidCreditCard", "isValidDate", "isValidDirectoryPath", "isValidDouble",
+        "isValidFileContent", "isValidFileName", "isValidInput", "isValidInteger",
+        "isValidListItem", "isValidNumber", "isValidPrintable", "isValidRedirectLocation",
+        "isValidSafeHTML", "isValidURI"
+      ])
+  }
+}
+
+/**
+ * The methods of `org.owasp.esapi.Validator` which return validated data.
+ */
+class EsapiGetValidMethod extends Method {
+  EsapiGetValidMethod() {
+    this.getDeclaringType() instanceof EsapiValidator and
+    this.hasName([
+        "getValidCreditCard", "getValidDate", "getValidDirectoryPath", "getValidDouble",
+        "getValidFileContent", "getValidFileName", "getValidInput", "getValidInteger",
+        "getValidListItem", "getValidNumber", "getValidPrintable", "getValidRedirectLocation",
+        "getValidSafeHTML", "getValidURI"
+      ])
+  }
+}
diff --git a/java/ql/lib/semmle/code/java/security/TrustBoundaryViolationQuery.qll b/java/ql/lib/semmle/code/java/security/TrustBoundaryViolationQuery.qll
index 60801fceff6..1f84f98018f 100644
--- a/java/ql/lib/semmle/code/java/security/TrustBoundaryViolationQuery.qll
+++ b/java/ql/lib/semmle/code/java/security/TrustBoundaryViolationQuery.qll
@@ -2,8 +2,10 @@
 
 import java
 private import semmle.code.java.dataflow.DataFlow
+private import semmle.code.java.controlflow.Guards
 private import semmle.code.java.dataflow.ExternalFlow
 private import semmle.code.java.dataflow.FlowSources
+private import semmle.code.java.frameworks.owasp.Esapi
 
 /**
  * A source of data that crosses a trust boundary.
@@ -26,6 +28,27 @@ class TrustBoundaryViolationSink extends DataFlow::Node {
 
 abstract class TrustBoundaryValidationSanitizer extends DataFlow::Node { }
 
+/**
+ * A node validated by an OWASP ESAPI validation method.
+ */
+private class EsapiValidatedInputSanitizer extends TrustBoundaryValidationSanitizer {
+  EsapiValidatedInputSanitizer() {
+    this = DataFlow::BarrierGuard<esapiIsValidData/3>::getABarrierNode() or
+    this.asExpr().(MethodAccess).getMethod() instanceof EsapiGetValidMethod
+  }
+}
+
+/**
+ * Holds if `g` is a guard that checks that `e` is valid data according to an OWASP ESAPI validation method.
+ */
+private predicate esapiIsValidData(Guard g, Expr e, boolean branch) {
+  branch = true and
+  exists(MethodAccess ma | ma.getMethod() instanceof EsapiIsValidMethod |
+    g = ma and
+    e = ma.getArgument(1)
+  )
+}
+
 /**
  * Taint tracking for data that crosses a trust boundary.
  */
diff --git a/java/ql/test/query-tests/security/CWE-501/TrustBoundaryViolations.java b/java/ql/test/query-tests/security/CWE-501/TrustBoundaryViolations.java
index 5bef7e087d2..9f9be44c972 100644
--- a/java/ql/test/query-tests/security/CWE-501/TrustBoundaryViolations.java
+++ b/java/ql/test/query-tests/security/CWE-501/TrustBoundaryViolations.java
@@ -2,11 +2,34 @@ import java.io.IOException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
+import org.owasp.esapi.Validator;
 
 public class TrustBoundaryViolations extends HttpServlet {
+    Validator validator;
+
     public void doGet(HttpServletRequest request, HttpServletResponse response) {
         String input = request.getParameter("input");
 
+        // BAD: The input is written to the response without being sanitized.
         request.getSession().setAttribute("input", input); // $ hasTaintFlow
+
+        String input2 = request.getParameter("input2");
+
+        try {
+            String sanitized = validator.getValidInput("HTTP parameter", input2, "HTTPParameterValue", 100, false);
+            // GOOD: The input is sanitized before being written to the response.
+            request.getSession().setAttribute("input2", sanitized);
+
+        } catch (Exception e) {
+        }
+
+        try {
+            String input3 = request.getParameter("input3");
+            if (validator.isValidInput("HTTP parameter", input3, "HTTPParameterValue", 100, false)) {
+                // GOOD: The input is sanitized before being written to the response.
+                request.getSession().setAttribute("input3", input3);
+            }
+        } catch (Exception e) {
+        }
     }
 }