CloudBees flaws in Jenkins server can lead to code execution

Pierluigi Paganini March 09, 2023

CloudBees vulnerabilities in the Jenkins open-source automation server can be exploited to achieve code execution on targeted systems.

Researchers from cloud security firm Aqua discovered a chain of two vulnerabilities in the Jenkins open-source automation server that could lead to code execution on targeted systems.

Jenkins is the most popular open source automation server, it is maintained by CloudBees and the Jenkins community. The automation server supports developers build, test and deploy their applications, it has hundreds of thousands of active installations worldwide with more than 1 million users.

The two flaws, tracked as CVE-2023-27898 and CVE-2023-27905, are collectively named CorePlague impacts Jenkins Server and Update Center.

“Exploiting these vulnerabilities could allow an unauthenticated attacker to execute arbitrary code on the victim’s Jenkins server, potentially leading to a complete compromise of the Jenkins server.” reads the advisory published by the company. “Furthermore, these vulnerabilities could be exploited even if the Jenkins server is not directly reachable by attackers and could also impact self-hosted Jenkins servers.”

Jenkins Server attacks

The flaws affect Jenkins servers running versions 2.270 through 2.393 (both inclusive), LTS 2.277.1 through 2.375.3 (both inclusive) are vulnerable. Jenkins Update Centers with versions below 3.15 are vulnerable. 

Aqua researchers reported that the issues are related to how Jenkins processes available plugins, allowing attackers to conduct attacks such as cross-site scripting (XSS) or achive remote code execution. 

The researchers discovered that the flaws are achieved through a stored XSS exploitable by a Jenkins plugin with a malicious core version, which attackers upload to the Jenkins Update Center

“Once the victim opens the Available Plugin Manager on their Jenkins Server, the XSS is triggered, allowing attackers to run arbitrary code on the Jenkins Server utilizing the Script Console API. Importantly, the vulnerability is triggered without any additional action from the victim, and the exploitation does not require the manipulated plugin to be installed.” continues the advisory.

The researchers pointed out that the flaws can be exploited also in attacks against Jenkins Servers that are not directly reachable because the public Jenkins Update Center, used to obtain available plugin lists, could be injected by attackers. 

According to the advisory, in order to exploit the flaw the malicious plugin must be compatible with the Jenkins server and it must be displayed on the main page of the available plugin feed.

“The Jenkins team implemented a site tiering mechanism to show only plugins that are compatible with the current Jenkins Server, meaning the requiredCore version of the plugin is older than the Jenkins Server.” continues the report. “Since the requiredCore version is older, the warning message shown earlier will not appear, and the requiredCore value will not be processed as HTML, making it safe from the XSS.” 

The flaws were reported to the company on January 2023, and the Jenkins team acknowledged the t and issued them released patches for Update Center and server.

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Pierluigi Paganini

(SecurityAffairs – hacking, CloudBees)

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