CVE-2021-21658: 
Java vulnerability analysis and mitigation

CVE-2021-21658 is a security vulnerability discovered in the Jenkins Nuget Plugin version 1.0 and earlier. The vulnerability was identified and reported by Kevin Guerroudj, with the CVE being created on January 4, 2021, and publicly disclosed on May 25, 2021. This vulnerability affects the Jenkins Nuget Plugin's XML parser implementation, specifically in the 'Build on NuGet updates' feature (Jenkins Advisory).

The vulnerability is classified as an XML External Entity (XXE) attack vulnerability with a Medium severity CVSS rating. The core issue stems from the plugin's failure to properly configure its XML parser to prevent XXE attacks, specifically in the 'Build on NuGet updates' feature. The vulnerability exists in version 1.0 and earlier versions of the Nuget Plugin (Jenkins Advisory).

When exploited, this vulnerability allows attackers with the ability to control the contents of the packages.config file in a workspace to have Jenkins parse a crafted XML document. This can lead to the extraction of secrets from the Jenkins controller or enable server-side request forgery attacks (Jenkins Advisory, OSS Security).

The vulnerability has been fixed in Nuget Plugin version 1.1, which disables external entity resolution for its XML parser. Users are advised to update to this version to mitigate the vulnerability. The fix was released as part of the Jenkins Security Advisory on May 25, 2021 (Jenkins Advisory).