diff --git a/src/main/java/org/dataone/security/TemporaryMitigationValve.java b/src/main/java/org/dataone/security/TemporaryMitigationValve.java
new file mode 100644
index 0000000..a86e489
--- /dev/null
+++ b/src/main/java/org/dataone/security/TemporaryMitigationValve.java
@@ -0,0 +1,105 @@
+/**
+ * This work was created by participants in the DataONE project, and is
+ * jointly copyrighted by participating institutions in DataONE. For 
+ * more information on DataONE, see our web site at http://dataone.org.
+ *
+ *   Copyright 2026
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and 
+ * limitations under the License.
+ * 
+ * $Id$
+ */
+
+package org.dataone.security;
+
+import java.io.IOException;
+import java.net.URLDecoder;
+import java.nio.charset.StandardCharsets;
+import java.util.regex.Pattern;
+
+import javax.servlet.ServletException;
+
+import org.apache.catalina.Valve;
+import org.apache.catalina.connector.Request;
+import org.apache.catalina.connector.Response;
+import org.apache.catalina.valves.ValveBase;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
+/**
+ * Temporary mitigation Valve to handle GHSA-95v2-fvxr-qg83-style path confusion/bypass attempts.
+ * Added 2026-07-10.
+ * Enable via the {@code <Valve>} element under {@code <Host ...>} in {@code server.xml}, e.g.:
+ *     {@code <Valve className="org.dataone.security.TemporaryMitigationValve" />}
+ */
+public class TemporaryMitigationValve extends ValveBase {
+
+    private static final Logger logger = LogManager.getLogger(TemporaryMitigationValve.class.getName());
+
+    private static final int MAX_DECODE_ROUNDS = 3;
+
+    // deny patterns
+    private static final Pattern SUSPICIOUS = Pattern.compile(
+        "(?i)(\\.{2}|%2e|%2f|%5c|\\\\|/\\./|/\\.\\./|%252e|%252f|%255c)"
+    );
+
+    @Override
+    public void invoke(Request request, Response response) throws IOException, ServletException {
+        String uri = safe(request.getRequestURI());
+        String qs = request.getQueryString();
+        String target = (qs == null) ? uri : (uri + "?" + qs);
+
+        if (isSuspicious(target)) {
+            logger.warn("Rejecting suspicious request from remote address {} for URI {}",
+                safe(request.getRemoteAddr()), uri);
+            response.sendError(400, "Malformed request target");
+            return;
+        }
+
+        Valve next = getNext();
+        if (next != null) {
+            next.invoke(request, response);
+        }
+    }
+
+    private boolean isSuspicious(String input) {
+        String current = input;
+        for (int i = 0; i < MAX_DECODE_ROUNDS; i++) {
+            if (SUSPICIOUS.matcher(current).find()) {
+                return true;
+            }
+            String decoded = decodeOnce(current);
+            if (decoded == null) {
+                return true;
+            }
+            if (decoded.equals(current)) {
+                break;
+            }
+            current = decoded;
+        }
+        return SUSPICIOUS.matcher(current).find();
+    }
+
+    private String decodeOnce(String value) {
+        try {
+            return URLDecoder.decode(value, StandardCharsets.UTF_8);
+        } catch (IllegalArgumentException e) {
+            // Invalid %-encoding: signal decode failure to caller.
+            return null;
+        }
+    }
+
+    private String safe(String v) {
+        return v == null ? "" : v;
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/org/dataone/security/TemporaryMitigationValveTest.java b/src/test/java/org/dataone/security/TemporaryMitigationValveTest.java
new file mode 100644
index 0000000..bae86dc
--- /dev/null
+++ b/src/test/java/org/dataone/security/TemporaryMitigationValveTest.java
@@ -0,0 +1,73 @@
+/**
+ * This work was created by participants in the DataONE project, and is
+ * jointly copyrighted by participating institutions in DataONE. For
+ * more information on DataONE, see our web site at http://dataone.org.
+ *
+ *   Copyright 2026
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * $Id$
+ */
+
+package org.dataone.security;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+import org.junit.Test;
+
+public class TemporaryMitigationValveTest {
+
+    private final TemporaryMitigationValve valve = new TemporaryMitigationValve();
+
+    @Test
+    public void rejectsPlainTraversal() {
+        assertTrue(isSuspicious("/v2/resolve/../etc/passwd"));
+    }
+
+    @Test
+    public void rejectsSingleEncodedTraversal() {
+        assertTrue(isSuspicious("/v2/resolve/%2e%2e%2fetc/passwd"));
+    }
+
+    @Test
+    public void rejectsDoubleEncodedTraversal() {
+        assertTrue(isSuspicious("/v2/resolve/%252e%252e%252fetc/passwd"));
+    }
+
+    @Test
+    public void rejectsMalformedPercentEncoding() {
+        assertTrue(isSuspicious("/v2/resolve/%ZZ"));
+    }
+
+    @Test
+    public void allowsNormalRequestTarget() {
+        assertFalse(isSuspicious("/v2/resolve/abc123?includeMetadata=true"));
+    }
+
+    private boolean isSuspicious(String input) {
+        try {
+            Method method = TemporaryMitigationValve.class.getDeclaredMethod("isSuspicious", String.class);
+            method.setAccessible(true);
+            return (Boolean) method.invoke(valve, input);
+        } catch (NoSuchMethodException | IllegalAccessException e) {
+            throw new AssertionError("Failed to access TemporaryMitigationValve.isSuspicious", e);
+        } catch (InvocationTargetException e) {
+            throw new AssertionError("Unexpected exception from TemporaryMitigationValve.isSuspicious", e);
+        }
+    }
+}