Chapter 2. Eclipse Temurin features

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Eclipse Temurin does not contain structural changes from the upstream distribution of OpenJDK.

For the list of changes and security fixes included in the latest OpenJDK 11.0.17 release of Eclipse Temurin, see OpenJDK 11.0.17 Released.

New features and enhancements

Review the following release notes to understand new features and feature enhancements included with the Eclipse Temurin 11.0.17 release:

Disabled cpu.shares parameter

Before the OpenJDK 11.0.17 release, OpenJDK used an incorrect interpretation of the cpu.shares parameter, which belongs to Linux control groups, also known as cgroups. The parameter might cause a Java Virtual machine (JVM) to use fewer CPUs than available, which can impact the JVM’s CPU resources and performance when it operates inside a container.

The OpenJDK 11.0.17 release configures a JVM to no longer use the cpu.shares parameter when determining the number of threads for a thread pool. If you want to revert this configuration, pass the -XX:+UseContainerCpuShares argument on JVM startup.


The -XX:+UseContainerCpuShares argument is a deprecated feature and might be removed in a future OpenJDK release.

See JDK-8281181 (JDK Bug System).

jdk.httpserver.maxConnections system property

OpenJDK 11.0.17 adds a new system property, jdk.httpserver.maxConnections, that fixes a security issue where no connection limits were specified for the HttpServer service, which can cause accepted connections and established connections to remain open indefinitely.

You can use the jdk.httpserver.maxConnections system property to change the HttpServer service, behavior in the following ways:

  • Set a value of 0 or a negative value, such as -1, to specify no connection limit for the service.
  • Set a positive value, such as 1, to cause the service to check any accepted connection against the current count of established connections. If the established connection for the service is reached, the service immediately closes the accepted connection.

See JDK-8286918 (JDK Bug System).

Monitor deserialization of objects with JFR

You can now monitor deserialization of objects with the JDK Flight Recorder (JFR). By default, OpenJDK 11.0.17 disables the jdk.deserialization event setting for JFR. You can enable this feature by updating the event-name element in your JFR configuration. For example:

<?xml version="1.0" encoding="UTF-8"?>
<configuration version="2.0" description="test">
 <event name="jdk.Deserialization">
 <setting name="enabled">true</setting>
 <setting name="stackTrace">false</setting>

After you enable JFR and you configure JFR to monitor deserialization events, JFR creates an event whenever a monitored application attempts to deserialize an object. The serialization filter mechanism of JFR can then determine whether to accept or reject a deserialized object from the monitored application.

See JDK-8261160 (JDK Bug System).

SHA-1 Signed JARs

With the OpenJDK 11.0.17 release, JARs signed with SHA-1 algorithms are restricted by default and treated as if they were unsigned. These restrictions apply to the following algorithms:

  • Algorithms used to digest, sign, and optionally timestamp the JAR.
  • Signature and digest algorithms of the certificates in the certificate chain of the code signer and the Timestamp Authority, and any Certificate Revocation Lists (CRLs) or Online Certificate Status Protocol (OCSP) responses that are used to verify if those certificates have been revoked.

Additionally, the restrictions apply to signed Java Cryptography Extension (JCE) providers.

To reduce the compatibility risk for JARs that have been previously timestamped, the restriction does not apply to any JAR signed with SHA-1 algorithms and timestamped prior to January 01, 2019. This exception might be removed in a future OpenJDK release.

To determine if your JAR file is impacted by the restriction, you can issue the following command in your CLI:

$ jarsigner -verify -verbose -certs

From the output of the previous command, search for instance of SHA1 , SHA-1, or disabled. Additionally, search for any warning messages that indicate that the JAR will be treated as unsigned. For example:

Signed by "CN="Signer""
Digest algorithm: SHA-1 (disabled)
Signature algorithm: SHA1withRSA (disabled), 2048-bit key

WARNING: The jar will be treated as unsigned, because it is signed with a weak algorithm that is now disabled by the security property:

jdk.jar.disabledAlgorithms=MD2, MD5, RSA keySize < 1024, DSA keySize < 1024, SHA1 denyAfter 2019-01-01

Consider replacing or re-signing any JARs affected by the new restrictions with stronger algorithms.

If your JAR file is impacted by this restriction, you can remove the algorithm and re-sign the file with a stronger algorithm, such as SHA-256. If you want to remove the restriction on SHA-1 signed JARs for OpenJDK 11.0.17, and you accept the security risks, you can complete the following actions:

  1. Modify the configuration file. Alternatively, you can preserve this file and instead create another file with the required configurations.
  2. Remove the SHA1 usage SignedJAR & denyAfter 2019 01 011 entry from the jdk.certpath.disabledAlgorithms security property.
  3. Remove the SHA1 denyAfter 2019-01-01 entry from the jdk.jar.disabledAlgorithms security property.

The value of jdk.certpath.disabledAlgorithms in the file might be overridden by the system security policy on RHEL 8 and 9. The values used by the system security policy can be seen in the file /etc/crypto-policies/back-ends/java.config and disabled by either setting security.useSystemPropertiesFile to false in the file or passing to the JVM. These values are not modified by this release, so the values remain the same for previous releases of OpenJDK.

For an example of configuring the file, see Overriding properties for JBoss EAP for OpenShift (Red Hat Customer Portal).

See JDK-8269039 (JDK Bug System).

System properties for controlling the keep-alive behavior of HTTPURLConnection

The OpenJDK 11.0.17 release includes the following new system properties that you can use to control the keep-alive behavior of HTTPURLConnection:

  • http.keepAlive.time.server, which controls connections to servers.
  • http.keepAlive.time.proxy, which controls connections to proxies.

Before the OpenJDK 11.0.17 release, a server or a proxy with an unspecified keep-alive time might cause an idle connection to remain open for a period defined by a hard-coded default value.

With OpenJDK 11.0.17, you can use system properties to change the default value for the keep-alive time. The keep-alive properties control this behavior by changing the HTTP keep-alive time of either a server or proxy, so that OpenJDK’s HTTP protocol handler closes idle connections after a specified number of seconds.

Before the OpenJDK 11.0.17 release, the following use cases would lead to specific keep-alive behaviors for HTTPURLConnection:

  • If the server specifies the Connection:keep-alive header and the server’s response contains Keep-alive:timeout=N then the OpenJDK keep-alive cache on the client uses a timeout of N seconds, where N is an integer value.
  • If the server specifies the Connection:keep-alive header, but the server’s response does not contain an entry for Keep-alive:timeout=N then the OpenJDK keep-alive cache on the client uses a timeout of 60 seconds for a proxy and 5 seconds for a server.
  • If the server does not specify the Connection:keep-alive header, the OpenJDK keep-alive cache on the client uses a timeout of 5 seconds for all connections.

The OpenJDK 11.0.17 release maintains the previously described behavior, but you can now specify the timeouts in the second and third listed use cases by using the http.keepAlive.time.server and http.keepAlive.time.proxy properties, rather than having to rely on the default settings.


If you set the keep-alive property and the server specifies a keep-alive time for the Keep-Alive response header, the HTTP protocol handler uses the time specified by the server. This situation is identical for a proxy.

See JDK-8278067 (JDK Bug System).

Updated the default PKCS #12 MAC algorithm

The OpenJDK 11.0.17 updates the default Message Authentication Code (MAC) algorithm for the PKCS #12 keystore to use the SHA-256 cryptographic hash function rather than the SHA-1 function. The SHA-256 function provides a stronger way to secure data.

You can view this update in the keystore.pkcs12.macAlgorithm and the keystore.pkcs12.maclterationCount system properties.

If you create a keystore with this updated MAC algorithm, and you attempt to use the keystore with an OpenJDK version earlier than OpenJDK 11.0.12, you would receive a message.

To use the previous keystore with an OpenJDK version that is earlier than OpenJDK 11.0.12, set the keystore.pkcs12.legacy system property to true to revert the MAC algorithm.

See JDK-8267880 (JDK Bug System).

Deprecated and removed features

Review the following release notes to understand pre-existing features that have been either deprecated or removed in the OpenJDK 11.0.17 release:

Deprecated Kerberos encryption types

OpenJDK 11.0.17 deprecates des3-hmac-sha1 and rc4-hmac Kerberos encryption types. By default, OpenJDK 11.0.17 disables these encryption types, but you can enable them by completing the following action:

  • In the krb5.conf configuration file, set the allow_weak_crypto tab to true. This configuration also enables other encryption types, such as des-cbc-crc and des-cbc-md5.

Before you apply this configuration, consider the risks of enabling all of these weak Kerberos encryption types, such as introducing weak encryption algorithms to your Kerberos’s authentication mechanism.

You can disable a subset of weak encryption types by explicitly listing an encryption type in one of the following krb5.conf configuration file’s settings:

  • default_tkt_enctypes
  • default_tgs_enctypes
  • permitted_enctypes

See JDK-8139348 (JDK Bug System).

Revised on 2024-05-09 16:45:57 UTC

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