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MINOR: Always compare the password in PlainServerCallbackHandler #24094

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MINOR: Always compare the password in PlainServerCallbackHandler #24094

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94e0708
MINOR: Always compare the password in PlainServerCallbackHandler
aashish-confluent Nov 3, 2026
5921055
Verify the password is compared for an unknown user
aashish-confluent Nov 3, 2026
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5 changes: 4 additions & 1 deletion ...ain/java/org/apache/kafka/common/security/plain/internals/PlainServerCallbackHandler.java
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@
public class PlainServerCallbackHandler implements AuthenticateCallbackHandler {

private static final String JAAS_USER_PREFIX = "user_";
private static final char[] UNKNOWN_USER_DUMMY_PASSWORD = {'\0'};
private List<AppConfigurationEntry> jaasConfigEntries;

@Override
Expand Down Expand Up @@ -65,7 +66,9 @@ protected boolean authenticate(String username, char[] password) throws IOExcept
String expectedPassword = JaasContext.configEntryOption(jaasConfigEntries,
JAAS_USER_PREFIX + username,
PlainLoginModule.class.getName());
return expectedPassword != null && Utils.isEqualConstantTime(password, expectedPassword.toCharArray());
char[] comparedPassword = expectedPassword != null ? expectedPassword.toCharArray() : UNKNOWN_USER_DUMMY_PASSWORD;
boolean matches = Utils.isEqualConstantTime(password, comparedPassword);
return matches && expectedPassword != null;
}
}

Expand Down
32 changes: 31 additions & 1 deletion ...s/src/test/java/org/apache/kafka/common/security/plain/internals/PlainSaslServerTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -20,16 +20,23 @@
import org.apache.kafka.common.security.JaasContext;
import org.apache.kafka.common.security.authenticator.TestJaasConfig;
import org.apache.kafka.common.security.plain.PlainLoginModule;
import org.apache.kafka.common.utils.Utils;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.mockito.MockedStatic;
import org.mockito.Mockito;

import java.nio.charset.StandardCharsets;
import java.util.HashMap;
import java.util.Map;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.mockito.AdditionalMatchers.aryEq;
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.Mockito.mockStatic;

public class PlainSaslServerTest {

Expand All @@ -38,6 +45,7 @@ public class PlainSaslServerTest {
private static final String USER_B = "userB";
private static final String PASSWORD_B = "passwordB";

private PlainServerCallbackHandler callbackHandler;
private PlainSaslServer saslServer;

@BeforeEach
Expand All @@ -48,7 +56,7 @@ public void setUp() {
options.put("user_" + USER_B, PASSWORD_B);
jaasConfig.addEntry("jaasContext", PlainLoginModule.class.getName(), options);
JaasContext jaasContext = new JaasContext("jaasContext", JaasContext.Type.SERVER, jaasConfig, null);
PlainServerCallbackHandler callbackHandler = new PlainServerCallbackHandler();
callbackHandler = new PlainServerCallbackHandler();
callbackHandler.configure(null, "PLAIN", jaasContext.configurationEntries());
saslServer = new PlainSaslServer(callbackHandler);
}
Expand All @@ -70,6 +78,28 @@ public void authorizationIdNotEqualsAuthenticationId() {
assertThrows(SaslAuthenticationException.class, () -> saslServer.evaluateResponse(saslMessage(USER_B, USER_A, PASSWORD_A)));
}

@Test
public void unknownUserOrInvalidPassword() throws Exception {
Exception e = assertThrows(SaslAuthenticationException.class, () ->
saslServer.evaluateResponse(saslMessage("", "unknownUser", PASSWORD_A)));
assertEquals("Authentication failed: Invalid username or password", e.getMessage());

e = assertThrows(SaslAuthenticationException.class, () ->
saslServer.evaluateResponse(saslMessage("", USER_A, PASSWORD_B)));
assertEquals("Authentication failed: Invalid username or password", e.getMessage());

assertFalse(callbackHandler.authenticate("unknownUser", new char[] {'\0'}));
}

@Test
public void passwordIsComparedForUnknownUser() {
try (MockedStatic<Utils> mockedUtils = mockStatic(Utils.class, Mockito.CALLS_REAL_METHODS)) {
assertThrows(SaslAuthenticationException.class, () ->
saslServer.evaluateResponse(saslMessage("", "unknownUser", PASSWORD_A)));
mockedUtils.verify(() -> Utils.isEqualConstantTime(aryEq(PASSWORD_A.toCharArray()), any(char[].class)));
}
}

@Test
public void emptyTokens() {
Exception e = assertThrows(SaslAuthenticationException.class, () ->
Expand Down
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