diff --git a/src/main/java/org/apache/commons/net/ftp/FTP.java b/src/main/java/org/apache/commons/net/ftp/FTP.java
index 07420b81d..2beebb0ef 100644
--- a/src/main/java/org/apache/commons/net/ftp/FTP.java
+++ b/src/main/java/org/apache/commons/net/ftp/FTP.java
@@ -427,6 +427,13 @@ public int appe(final String path) throws IOException {
         return sendCommand(FTPCmd.APPE, path);
     }
 
+    private static void checkCRLF(final String command, final String args) {
+        if (command != null && (command.indexOf('\r') >= 0 || command.indexOf('\n') >= 0)
+                || args != null && (args.indexOf('\r') >= 0 || args.indexOf('\n') >= 0)) {
+            throw new IllegalArgumentException("Commands and arguments cannot contain CR or LF characters");
+        }
+    }
+
     private String buildMessage(final String command, final String args) {
         final StringBuilder builder = new StringBuilder(command);
         if (args != null) {
@@ -1296,6 +1303,7 @@ public int sendCommand(final String command) throws IOException {
      * @throws IOException                  If an I/O error occurs while either sending the command or receiving the server reply.
      */
     public int sendCommand(final String command, final String args) throws IOException {
+        checkCRLF(command, args);
         if (_controlOutput_ == null) {
             throw new IOException("Connection is not open");
         }
diff --git a/src/main/java/org/apache/commons/net/nntp/NNTP.java b/src/main/java/org/apache/commons/net/nntp/NNTP.java
index c6430cefa..7130df028 100644
--- a/src/main/java/org/apache/commons/net/nntp/NNTP.java
+++ b/src/main/java/org/apache/commons/net/nntp/NNTP.java
@@ -641,6 +641,10 @@ public int sendCommand(final String command) throws IOException {
      * @throws IOException                   If an I/O error occurs while either sending the command or receiving the server reply.
      */
     public int sendCommand(final String command, final String args) throws IOException {
+        if (command != null && (command.indexOf('\r') >= 0 || command.indexOf('\n') >= 0)
+                || args != null && (args.indexOf('\r') >= 0 || args.indexOf('\n') >= 0)) {
+            throw new IllegalArgumentException("Commands and arguments cannot contain CR or LF characters");
+        }
         final StringBuilder builder = new StringBuilder(command);
         if (args != null) {
             builder.append(' ');
diff --git a/src/main/java/org/apache/commons/net/pop3/POP3.java b/src/main/java/org/apache/commons/net/pop3/POP3.java
index a93561ef1..2db9c2f44 100644
--- a/src/main/java/org/apache/commons/net/pop3/POP3.java
+++ b/src/main/java/org/apache/commons/net/pop3/POP3.java
@@ -277,6 +277,10 @@ public int sendCommand(final String command) throws IOException {
      * @throws IOException on error
      */
     public int sendCommand(final String command, final String args) throws IOException {
+        if (command != null && (command.indexOf('\r') >= 0 || command.indexOf('\n') >= 0)
+                || args != null && (args.indexOf('\r') >= 0 || args.indexOf('\n') >= 0)) {
+            throw new IllegalArgumentException("Commands and arguments cannot contain CR or LF characters");
+        }
         if (writer == null) {
             throw new IllegalStateException("Socket is not connected");
         }
diff --git a/src/main/java/org/apache/commons/net/smtp/SMTP.java b/src/main/java/org/apache/commons/net/smtp/SMTP.java
index 6102397cd..9c85ea5cf 100644
--- a/src/main/java/org/apache/commons/net/smtp/SMTP.java
+++ b/src/main/java/org/apache/commons/net/smtp/SMTP.java
@@ -517,6 +517,10 @@ public int sendCommand(final String command, final String args) throws IOExcepti
      * @throws IOException
      */
     private int sendCommand(final String command, final String args, final boolean includeSpace) throws IOException {
+        if (command != null && (command.indexOf('\r') >= 0 || command.indexOf('\n') >= 0)
+                || args != null && (args.indexOf('\r') >= 0 || args.indexOf('\n') >= 0)) {
+            throw new IllegalArgumentException("Commands and arguments cannot contain CR or LF characters");
+        }
         final StringBuilder builder = new StringBuilder(command);
         if (args != null) {
             if (includeSpace) {
diff --git a/src/test/java/org/apache/commons/net/ftp/FTPTest.java b/src/test/java/org/apache/commons/net/ftp/FTPTest.java
new file mode 100644
index 000000000..07ecf4e39
--- /dev/null
+++ b/src/test/java/org/apache/commons/net/ftp/FTPTest.java
@@ -0,0 +1,45 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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
+ *
+ *      https://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.
+ */
+
+package org.apache.commons.net.ftp;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+class FTPTest {
+
+    @Test
+    void testRejectCRInArgs() {
+        assertThrows(IllegalArgumentException.class, () -> new FTP().sendCommand("RETR", "file\rDELE secret"));
+    }
+
+    @Test
+    void testRejectCRLFInArgs() {
+        assertThrows(IllegalArgumentException.class, () -> new FTP().sendCommand("RETR", "file\r\nDELE secret"));
+    }
+
+    @Test
+    void testRejectLFInArgs() {
+        assertThrows(IllegalArgumentException.class, () -> new FTP().sendCommand("RETR", "file\nDELE secret"));
+    }
+
+    @Test
+    void testRejectLFInCommand() {
+        assertThrows(IllegalArgumentException.class, () -> new FTP().sendCommand("NOOP\nDELE secret"));
+    }
+}
diff --git a/src/test/java/org/apache/commons/net/nntp/NNTPTest.java b/src/test/java/org/apache/commons/net/nntp/NNTPTest.java
new file mode 100644
index 000000000..4144b7a22
--- /dev/null
+++ b/src/test/java/org/apache/commons/net/nntp/NNTPTest.java
@@ -0,0 +1,45 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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
+ *
+ *      https://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.
+ */
+
+package org.apache.commons.net.nntp;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+class NNTPTest {
+
+    @Test
+    void testRejectCRInArgs() {
+        assertThrows(IllegalArgumentException.class, () -> new NNTP().sendCommand("GROUP", "news\rQUIT"));
+    }
+
+    @Test
+    void testRejectCRLFInArgs() {
+        assertThrows(IllegalArgumentException.class, () -> new NNTP().sendCommand("GROUP", "news\r\nQUIT"));
+    }
+
+    @Test
+    void testRejectLFInArgs() {
+        assertThrows(IllegalArgumentException.class, () -> new NNTP().sendCommand("GROUP", "news\nQUIT"));
+    }
+
+    @Test
+    void testRejectLFInCommand() {
+        assertThrows(IllegalArgumentException.class, () -> new NNTP().sendCommand("NOOP\nQUIT"));
+    }
+}
diff --git a/src/test/java/org/apache/commons/net/pop3/POP3Test.java b/src/test/java/org/apache/commons/net/pop3/POP3Test.java
new file mode 100644
index 000000000..c49009bc7
--- /dev/null
+++ b/src/test/java/org/apache/commons/net/pop3/POP3Test.java
@@ -0,0 +1,45 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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
+ *
+ *      https://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.
+ */
+
+package org.apache.commons.net.pop3;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+class POP3Test {
+
+    @Test
+    void testRejectCRInArgs() {
+        assertThrows(IllegalArgumentException.class, () -> new POP3().sendCommand("USER", "name\rPASS x"));
+    }
+
+    @Test
+    void testRejectCRLFInArgs() {
+        assertThrows(IllegalArgumentException.class, () -> new POP3().sendCommand("USER", "name\r\nPASS x"));
+    }
+
+    @Test
+    void testRejectLFInArgs() {
+        assertThrows(IllegalArgumentException.class, () -> new POP3().sendCommand("USER", "name\nPASS x"));
+    }
+
+    @Test
+    void testRejectLFInCommand() {
+        assertThrows(IllegalArgumentException.class, () -> new POP3().sendCommand("NOOP\nPASS x"));
+    }
+}
diff --git a/src/test/java/org/apache/commons/net/smtp/SMTPTest.java b/src/test/java/org/apache/commons/net/smtp/SMTPTest.java
new file mode 100644
index 000000000..73877c90d
--- /dev/null
+++ b/src/test/java/org/apache/commons/net/smtp/SMTPTest.java
@@ -0,0 +1,45 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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
+ *
+ *      https://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.
+ */
+
+package org.apache.commons.net.smtp;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+class SMTPTest {
+
+    @Test
+    void testRejectCRInArgs() {
+        assertThrows(IllegalArgumentException.class, () -> new SMTP().sendCommand("MAIL", "FROM:<a@b>\rRCPT TO:<c@d>"));
+    }
+
+    @Test
+    void testRejectCRLFInArgs() {
+        assertThrows(IllegalArgumentException.class, () -> new SMTP().sendCommand("MAIL", "FROM:<a@b>\r\nRCPT TO:<c@d>"));
+    }
+
+    @Test
+    void testRejectLFInArgs() {
+        assertThrows(IllegalArgumentException.class, () -> new SMTP().sendCommand("MAIL", "FROM:<a@b>\nRCPT TO:<c@d>"));
+    }
+
+    @Test
+    void testRejectLFInCommand() {
+        assertThrows(IllegalArgumentException.class, () -> new SMTP().sendCommand("NOOP\nRSET"));
+    }
+}