CVE-2021-21639 Lack of type validation in agent related REST API in Jenkins

What is CVE-2021-21639?

CVE-2021-21639 is a medium-severity unsafe deserialization vulnerability in Jenkins Jenkins, published on 7 Apr 2021. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Jenkins 2.286 and earlier, LTS 2.277.1 and earlier does not validate the type of object created after loading the data submitted to the `config.xml` REST API endpoint of a node, allowing attackers with Computer/Configure permission to replace a node with one of a different type.

Which versions are affected by CVE-2021-21639?

5 open source packages ship an affected version, including org.jenkins-ci.main:jenkins-core and jenkins. It affects 1 product.

Products include Jenkins Jenkins.

How do I fix CVE-2021-21639?

Upgrade org.jenkins-ci.main:jenkins-core to a fixed version for your release line: 2.277.2 or 2.287.

Upgrade, and only deserialise data from trusted sources or with an allow-list of types. More about Unsafe deserialization.

Is CVE-2021-21639 being exploited?

There is no known exploitation of CVE-2021-21639 in the wild and no public exploit code.

Other vulnerabilities in Jenkins Jenkins

• CVE-2024-23897 Jenkins Command Line Interface (CLI) Path Traversal Exploited Critical 9.8
• CVE-2018-1000861 Jenkins Stapler Web Framework Deserialization of Untrusted Data Exploited Critical 9.8
• CVE-2017-1000353 Jenkins Remote Code Execution Exploited Critical 9.8
• CVE-2015-5317 Jenkins User Interface (UI) Information Disclosure Exploited High 7.5
• CVE-2021-21690 Multiple vulnerabilities allow bypassing path filtering of agent-to-controller access control in Jenkins Critical 9.8

All Jenkins Jenkins vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BIT-jenkins-2021-21639, GHSA-pvwx-3jx5-24r2.